CHANGELOG.md
In igraph: Network Analysis and Visualization

igraph C library changelog

igraph_bitset_update() copies the contents of one bitset into another (experimental function).
igraph_vector_sort_ind() (rename of igraph_vector_qsort_ind()).
igraph_vector_contains_sorted() (rename of igraph_vector_binsearch2()).
igraph_vector_reverse_section() reverses a contiguous section of a vector.
igraph_vector_rotate_left() applies a cyclic permutation to a vector.
igraph_strvector_swap_elements() swaps two strings in an igraph_strvector_t.
igraph_find_cycle() finds a single cycle in a graph, if it exists (experimental function).
igraph_feedback_vertex_set() finds a minimum feedback vertex set in a directed or undirected graph (experimental function).

igraph_feedback_arc_set() uses a much faster method for solving the exact minimum feedback arc set problem. The new method (IGRAPH_FAS_EXACT_IP_CG) is used by default (i.e. with IGRAPH_FAS_EXACT_IP), but the previous method is also kept available (IGRAPH_FAS_EXACT_IP_TI).
igraph_motifs_randesu(), igraph_motifs_randesu_callback(), igraph_motifs_randesu_estimate() and igraph_motifs_randesu_no() now accept NULL for their cut_prob parameter, signifying that a complete search should be performed.
igraph_centralization_eigenvector_centrality_tmax() and igraph_centralization_eigenvector_centrality() cannot produce meaningful results without normalizing vertex-level eigenvector centrality in a well-defined way. This was not the case when using scale=false. These functions now ignore the value of the scale parameter and always scale vertex-level centrality scores to have a maximum of 1. If you require a different type of normalization for the vertex-level eigenvector centrality scores, perform this normalization manually, and call igraph_centralization() to compute the centralization.
When igraph_eigenvector_centrality() receives a directed acyclic graph as input, it now produces an eigenvector which has 1s in sink vertices and 0s everywhere else. Previously, it would return an all-zero vector. Note that eigenvector centrality is not uniquely defined for graphs that are not (strongly) connected, and both of these results can be considered valid. This change is to ensure consistency with the definition of the theoretical maximum of eigenvector centralization, which assumes the in-star to be the most centralized directed network.

igraph_layout_drl() and igraph_layout_drl_3d() would crash with an assertion failure when interrupted. This is now fixed.
Removed broken interruption support from igraph_community_spinglass_single().
In rare cases igraph_community_multilevel() could enter an infinite loop. This is now corrected.
Fixed null-dereference in igraph_community_voronoi() when requesting modularity but not membership.
Fixed null-dereference in igraph_community_optimal_modularity() when requesting modularity but not membership and passing a null graph or singleton graph.
igraph_layout_umap() and igraph_layout_umap_3d() would crash when passing distances=NULL and distances_are_weights=true. This is now fixed.
igraph_layout_umap() and igraph_layout_umap_3d() would crash on interruption. This is now fixed.
igraph_read_graph_pajek() now warns about duplicate vertex IDs in input files.
The documented igraph_strvector_resize_min() was missing from headers.
igraph_feedback_arc_set() now validates the edge weights.
igraph_layout_lgl() was not working correctly since igraph 0.10.0 due to a poor choice of initial coordinates. This is now fixed.
igraph_centralization_degree_tmax(), igraph_centralization_betweenness_tmax(), igraph_centralization_closeness_tmax(), and igraph_centralization_eigenvector_centrality_tmax() now validate their nodes parameter.
igraph_centralization_degree_tmax(), igraph_centralization_betweenness_tmax(), igraph_centralization_closeness_tmax(), and igraph_centralization_eigenvector_centrality_tmax() now return NaN for zero-vertex graphs. Previously they would return invalid values.
igraph_centralization_eigenvector_centrality_tmax() now returns 0 for the undirected singleton graph. Previous it would return an invalid value.

igraph_minimum_spanning_tree_prim() and igraph_minimum_spanning_tree_unweighted() are deprecated. Use igraph_minimum_spanning_tree() in conjunction with igraph_subgraph_from_edges() instead.
igraph_array3_t and all associated functions are deprecated and scheduled for removal in igraph 1.0.
igraph_vector_qsort_ind() is deprecated in favour of igraph_vector_sort_ind().
igraph_vector_binsearch2() is deprecated in favour of igraph_vector_contains_sorted().

Fixed multiple memory leaks in benchmark programs.
Documentation improvements.

igraph_bitset_fill() sets all elements of a bitset to the same value (experimental function).
igraph_bitset_null() clears all elements of a bitset (experimental function).
igraph_bitset_is_all_zero(), igraph_bitset_is_all_one(), igraph_bitset_is_any_zero(), igraph_bitset_is_any_one() check if any/all elements of a bitset are zeros/ones (experimental functions).
igraph_chung_lu_game() implements the classic Chung-Lu model, as well as a number of its variants (experimental function).
igraph_mean_degree() computes the average of vertex degrees (experimental function).
igraph_count_loops() counts self-loops in the graph (experimental function).
igraph_is_clique() checks if all pairs within a set of vertices are connected (experimental function).
igraph_is_independent_vertex_set() checks if no pairs within a set of vertices are connected (experimental function).
igraph_hypercube() creates a hypercube graph (experimental function).
igraph_vector_intersection_size_sorted() counts elements common to two sorted vectors (experimental function).
igraph_stack_capacity() returns the allocated capacity of a stack.
igraph_vector_is_all_finite() checks if all elements in a vector are finite (i.e. neither NaN nor Inf).

Fixed a bug that incorrectly cached that a graph has no multiple edges when igraph_init_adjlist() was called with IGRAPH_NO_LOOPS and IGRAPH_NO_MULTIPLE and all the multi-edges were loop edges.
igraph_is_forest() would fail to set the result variable when testing for a directed forest, and it was already cached that the graph was not an undirected forest.
igraph_hub_and_authority_scores() no longer clips negative results to zeros when negative weights are present.
Fixed an assertion failure in igraph_realize_bipartite_degree_sequence() with some non-graphical degree sequences when requesting simple bipartite graphs.
igraph_static_fitness_game() checks the input more carefully, and avoids an infinite loop in rare edge cases, such as when (almost) all fitness scores are zero.
igraph_arpack_rnsolve() used the incorrect error message text for some errors. This is now corrected.
Corrected the detection of some MSVC-specific bitset intrinsics during configuration.
Corrected a bug in the fallback implementation of igraph_bitset_countl_zero() when IGRAPH_INTEGER_SIZE was set to 32. This fallback implementation was not used with GCC, Clang, or MSVC.

igraph_is_graphical() and igraph_is_bigraphical() are now linear-time in all cases, and generally several times faster than before (thanks to @gendelpiekel, contributed in #2605).
igraph_erdos_renyi_game_gnp() can now generate graphs with more than a hundred million vertices.
igraph_hub_and_authority_scores() now warns when negative edge weights are present.
igraph_layout_lgl() now uses a BFS tree rooted in the vertex specified as proot to guide the layout. Previously it used an unspecified (arbitrary) spanning tree.
Updated the internal heuristics used by igraph's ARPACK interface, igraph_arpack_rssolve() and igraph_arpack_rnsolve(), to improve the robustness of calculations.
Updated the initial vector construction in igraph_hub_and_authority_scores(), igraph_eigenvector_centrality() and igraph_(personalized_)pagerank() with IGRAPH_PAGERANK_ALGO_ARPACK. This improves the robustness and convergence of calculations.

Documentation improvements.
Reduced the memory usage of several functions by using bitsets instead of boolean vectors.
igraph_vector_intersect_sorted() has better performance when the input vector sizes are similar.

igraph_transitive_closure() computes the transitive closure of a graph (experimental function).
igraph_reachability() determines which vertices are reachable from each other in a graph (experimental function).
igraph_count_reachable() counts how many vertices are reachable from each vertex (experimental function).
Added a bitset data structure, igraph_bitset_t, and a set of corresponding functions (experimental functionality).

igraph_community_label_propagation() is now interruptible.
igraph_is_bipartite() would on rare occasions return invalid results when the cache was employed.
igraph_weighted_adjacency() correctly passes through NaN values with IGRAPH_ADJ_MAX, and correctly recognizes symmetric adjacency matrices containing NaN values with IGRAPH_ADJ_UNDIRECTED.
igraph_read_graph_gml() can now read GML files that use ids larger than what is representable on 32 bits, provided that igraph was configured with a 64-bit igraph_integer_t size.
Fixed a performance issue in igraph_read_graph_graphml() with files containing a very large number of entities, such as >.
igraph_read_graph_pajek() has improved vertex ID validation that better matches that of Pajek's own behavior.

igraph_eigenvector_centrality() no longer issues a warning when the input is directed and weighted. When using this function, keep in mind that eigenvector centrality is well-defined only for (strongly) connected graphs, and edges with zero weights are effectively treated as absent.

igraph_transitive_closure_dag() is deprecated in favour of igraph_transitive_closure()

Documentation improvements.
igraph_strength() and igraph_degree(loops=false) are now faster when calculating values for all vertices (contributed by @gendelpiekel in #2602)

igraph_is_complete() checks whether there is a connection between all pairs of vertices (experimental function, contributed by Aymeric Agon-Rambosson @aagon in #2510).
igraph_join() creates the join of two graphs (experimental function, contributed by Quinn Buratynski @GanzuraTheConsumer in #2508).

Fixed a corruption of the "finally" stack in igraph_write_graph_gml() for certain invalid GML files.
Fixed a memory leak in igraph_write_graph_lgl() when vertex names were present but edge weights were not.
Fixed the handling of duplicate edge IDs in igraph_subgraph_from_edges().
Fixed conversion of sparse matrices to dense with igraph_sparsemat_as_matrix() when sparse matrix object did not make use of its full allocated capacity.
igraph_write_graph_ncol() and igraph_write_graph_lgl() now refuse to write vertex names which would result in an invalid file that cannot be read back in.
igraph_write_graph_gml() now ignores graph attributes called edge or node with a warning. Writing these would create an invalid GML file that igraph couldn't read back.
igraph_disjoint_union() and igraph_disjoint_union_many() now check for overflow.
igraph_read_graph_graphml() now correctly compares attribute values with certain expected values, meaning that prefixes of valid values of attr.type are not accepted anymore.
Empty IDs are not allowed any more in <key> tags of GraphML files as this is a violation of the GraphML specification.
igraph_is_separator() and igraph_is_minimal_separator() now work correctly with disconnected graphs.
igraph_linegraph() now considers self-loops to be self-adjacent in undirected graphs, bringing consistency with how directed graphs were already handled in previous versions.
igraph_all_st_mincuts() now correctly returns all minimum cuts. This also fixes a problem with igraph_minimum_size_separators().
Corrected minor error in igraph_community_label_propagation() when adding labels to isolated nodes with some fixed labels present.
igraph_community_spinglass() no longer crashes when passing an edgeless graph and an empty weight vector.
igraph_rewire() no longer crashes on graphs with more than three vertices but fewer than two edges.

igraph_rewire() on longer throws an error on graphs with fewer than four vertices. These graphs are now returned unchanged, just like other graphs which are the unique realization of their degree sequence.

Performance: igraph_is_simple() now makes more granular use of the cache.
Performance: igraph_degree() now makes use of the cache when checking for self-loops.
The performance of igraph_is_minimal_separator() was improved.
igraph_is_graphical() now performs graphicality checks for degree sequences of simple directed graphs in linear time, an improvement from the previously used quadratic algorithm (contributed by Arnar Bjarni Arnarson @Tagl in #2537).
Documentation improvements.

When igraph_is_forest() determined that a graph is not a directed forest, and the roots output parameter was set to NULL, it would incorrectly cache that the graph is also not an undirected forest.
igraph_spanner() now correctly ignores edge directions, and no longer crashes on directed graphs.

igraph_are_connected() is renamed to igraph_are_adjacent(); the old name is kept available until at least igraph 1.0.

Documentation improvements.

igraph_is_biconnected() checks if a graph is biconnected.
igraph_realize_bipartite_degree_sequence() constructs a bipartite graph that has the given bidegree sequence, optionally ensuring that it is connected (PR #2425 by Lára Margrét Hólmfríðardóttir @larah19).

More robust error handling in HRG code.
Fixed infinite loop in igraph_hrg_sample_many().
igraph_community_fastgreedy() no longer crashes when providing a modularity vector only, but not a merges matrix of membership vector.
The graph property cache was not initialized correctly on systems where the size of bool was not 1 byte (#2477).
Compatibility with libxml2 version 2.12 (#2442).

The macro STR() is deprecated; use the function igraph_strvector_get() instead.

Performance: Reduced memory usage and improved initialization performance for igraph_strvector_t.
Performance: Improved cache use by igraph_is_bipartite().
The documentation is now also generated in Texinfo format.
Documentation improvements.

igraph_joint_degree_matrix() computes the joint degree matrix, i.e. counts connections between vertices of different degrees (PR #2407 by Lára Margrét Hólmfríðardóttir @larah19).
igraph_joint_degree_distribution() computes the joint distribution of degrees at either end of edges.
igraph_joint_type_distribution() computes the joint distribution of vertex categories at either end of edges, i.e. the mixing matrix.
igraph_degree_correlation_vector() computes the degree correlation function and its various directed generalizations.

The behaviour of the Pajek format reader and writer is now more closely aligned with the Pajek software and the reader is more tolerant of input it cannot interpret. Only those vertex and edge parameters are treated as valid which Pajek itself understands, therefore support for size is now dropped, and support for the font edge parameter is added. See http://mrvar.fdv.uni-lj.si/pajek/DrawEPS.htm for more information. Invalid/unrecognized parameters are now converted to igraph attributes by the reader, but just as before, they are not output by the writer.
The Pajek format writer now encodes newline and quotation mark characters in a Pajek-compatible manner (\n and ", respectively).
igraph_avg_nearest_neighbor_degree() now supports non-simple graphs.

Resolved "ignoring duplicate libraries" warning when building tests with Xcode 15 on macOS.
Fixed the handling of duplicate vertex IDs in igraph_induced_subgraph().
igraph_vector_which_min() and igraph_vector_which_max() no longer allow zero-length input, which makes them consistent with other similar functions, and was the originally intended behaviour. Passing zero-length input is invalid use and currently triggers an assertion failure.
igraph_erdos_renyi_game_gnm() and igraph_erdos_renyi_game_gnp() are now interruptible.
igraph_de_bruijn() and igraph_kautz() are now interruptible.
igraph_full(), igraph_full_citation(), igraph_full_multipartite() and igraph_turan() are now interruptible.
igraph_avg_nearest_neighbor_degree() did not compute knnk correctly in the weighted case.
Fixed variadic arguments of invalid types, which could cause incorrect behaviour with igraph_matrix_print(), as well as test suite failures, on some platforms. 32-bit x86 was affected when setting IGRAPH_INTEGER_SIZE to 64.
igraph_subisomorphic_lad() now returns a single null map when the pattern is the null graph.
igraph_community_spinglass() now checks its parameters more carefully.
igraph_similarity_dice_pairs() and igraph_similarity_jaccard_pairs() now validate vertex IDs.
igraph_maxflow() now returns an error code if the source and target vertices are the same. It used to get stuck in an infinite loop in earlier versions when the flow argument was non-NULL.

Updated vendored mini-gmp to 6.3.0.
igraph_connected_components() makes better use of the cache, improving overall performance.
Documentation improvements.

igraph_radius_dijkstra() computes the graph radius with weighted edges (experimental function).
igraph_graph_center_dijkstra() computes the graph center, i.e. the set of minimum eccentricity vertices, with weighted edges (experimental function).

igraph_full_bipartite() now checks for overflow.
igraph_bipartite_game_gnm() and igraph_bipartite_game_gnp() are now more robust to overflow.
Bipartite graph creation functions now check input arguments.
igraph_write_graph_dot() now quotes real numbers written in exponential notation as necessary.
Independent vertex set finding functions could trigger the fatal error "Finally stack too large" when called on large graphs.

igraph_bipartite_game() is now deprecated; use igraph_bipartite_game_gnm() and igraph_bipartite_game_gnp() instead.

Documentation improvements.

Compatibility with libxml2 2.11.
Fixed some converge failures in igraph_community_voronoi().
IGRAPH_CALLOC() and IGRAPH_REALLOC() now check for overflow.
CMake packages created with the install target of the CMake build system are now relocatable, i.e. the generated igraph-targets.cmake file does not contain absolute paths any more.

igraph_graph_power() computes the kth power of a graph (experimental function).
igraph_community_voronoi() for detecting communities using Voronoi partitioning (experimental function).

igraph_community_walktrap() no longer requires modularity and merges to be non-NULL when membership is non-NULL.
igraph_isomorphic() now supports multigraphs.
Shortest path related functions now consistently ignore edges with positive infinite weights.

igraph_hub_and_authority_scores(), igraph_hub_score() and igraph_authority_score() considered self-loops only once on the diagonal of the adjacency matrix of undirected graphs, thus the result was not identical to that obtained by igraph_eigenvector_centrality() on loopy undirected graphs. This is now corrected.
igraph_community_infomap() now checks edge and vertex weights for validity.
igraph_minimum_spanning_tree() and igraph_minimum_spanning_tree_prim() now check that edge weights are not NaN.
Fixed an initialization error in the string attribute combiner of the C attribute handler.
Fixed an issue with the weighted clique number calculation when all the weights were the same.
HRG functions now require a graph with at least 3 vertices; previous versions crashed with smaller graphs.
igraph_arpack_rssolve() and igraph_arpack_rnsolve(), i.e. the ARPACK interface in igraph, are now interruptible. As a result, several other functions that rely on ARPACK (eigenvector centrality, hub and authority scores, etc.) also became interruptible.
igraph_get_shortest_paths_dijkstra(), igraph_get_all_shortest_paths_dijkstra() and igraph_get_shortest_paths_bellman_ford() now validate the from vertex.
Fixed bugs in igraph_local_scan_1_ecount() for weighted undirected graphs which would miscount loops and multi-edges.

igraph_automorphisms() is now deprecated; its new name is igraph_count_automorphisms(). The old name is kept available until at least igraph 0.11.
igraph_hub_score() and igraph_authority_score() are now deprecated. Use igraph_hub_and_authority_scores() instead.
igraph_get_incidence() is now deprecated; its new name is igraph_get_biadjacency() to reflect that the returned matrix is an adjacency matrix between pairs of vertices and not an incidence matrix between vertices and edges. The new name is kept available until at least igraph 0.11. We plan to re-use the name in later versions to provide a proper incidence matrix where the rows are vertices and the columns are edges.
igraph_hrg_dendrogram() is deprecated because it requires an attribute handler and it goes against the convention of returning attributes in vectors where possible. Use igraph_from_hrg_dendrogram() instead, which constructs the dendrogram as an igraph graph and returns the associated probabilities in a vector.

Improved performance for igraph_vertex_connectivity().
igraph_simplify() makes use of the cache, and avoids simplification when the graph is already known to be simple.
Documentation improvements.

igraph_get_shortest_path_astar() finds a shortest path with the A* algorithm.
igraph_vertex_coloring_greedy() now supports the DSatur heuristics through IGRAPH_COLORING_GREEDY_DSATUR (#2284, thanks to @professorcode1).

The test build target now only runs the unit tests, but it does not build them. In order to both build and run tests, use the check target, which continues to behave as before (PR #2291).
The experimental function igraph_distances_floyd_warshall() now has from and to parameters for choosing source and target vertices.
The experimental function igraph_distances_floyd_warshall() now has an additional method parameter to select a specific algorithm. A faster "Tree" variant of the Floyd-Warshall algorithm is now available (#2267, thanks to @rfulekjames).

The Bellman-Ford shortest path finder is now interruptible.
The Floyd-Warshall shortest path finder is now interruptible.
Running CTest no longer builds the tests automatically, as this interfered with VSCode, which would invoke the ctest executable after configuring a project in order to determine test executables. Use the build_tests target to build the tests first, or use the check target to both build and run all unit tests (PR #2291).

Improved the performance and memory usage of igraph_widest_path_widths_floyd_warshall().
Documentation improvements.

igraph_matrix_init_array() to initialize an igraph matrix by copying an existing C array in column-major or row-major order.
igraph_layout_umap_compute_weights() computes weights for the UMAP layout algorithm from distances. This used to be part of igraph_layout_umap(), but it is now in a separate function to allow the user to experiment with different weighting schemes.
igraph_triangular_lattice() to generate triangular lattices of various kinds (#2235, thanks to @rfulekjames).
igraph_hexagonal_lattice() to generate hexagonal lattices of various kinds (#2262, thanks to @rfulekjames).
igraph_tree_from_parent_vector() to create a tree or a forest from a parent vector (i.e. a vector that encodes the parent vertex of each vertex).
igraph_induced_subgraph_edges() produces the IDs of edges contained within a subgraph induced by the given vertices.

The signature of the experimental igraph_layout_umap() function changed; the last argument is now a Boolean that specifies whether distances should already be treated as weights, and the sampling probability argument was removed.

igraph_transitivity_barrat(), igraph_community_fluid_communities(), igraph_sir(), igraph_trussness() and graphlet functions did not correctly detect when a directed input graph had effective multi-edges due to ignoring edge directions. Such graphs are now rejected by these functions.
Fixed a bug in igraph_2dgrid_move() that sometimes crashed the Large Graph Layout function when a grid cell became empty.
igraph_pagerank() and igraph_personalized_pagerank() would fail to converge when the ARPACK implementation was used and a vertex had more than one outgoing edge but all these edges had zero weights.
igraph_pagerank() and igraph_personalized_pagerank() no longer allow negative weights. Previously, edges with negative weights were silently ignored when using the PRPACK implementation. The ARPACK implementation would issue a warning saying that they are ignored, but in fact it computed an incorrect result.
igraph_all_st_cuts() and igraph_all_st_mincuts() no longer trigger the "Finally stack too large" fatal error when called on certain large graphs. This was a regression in igraph 0.10.
igraph_community_label_propagation() no longer rounds weights to integers. This was a regression in igraph 0.10.
igraph_read_graph_graphdb() does more thorough checks on the input file.
igraph_calloc() did not zero-initialize the allocated memory. This is now corrected. Note that the macro IGRAPH_CALLOC() was not affected.
Fixed new warnings issued by the Xcode 14.1 toolchain.

igraph_subgraph_edges() is now deprecated to avoid confusion with igraph_induced_subgraph_edges(); its new name is igraph_subgraph_from_edges(). The old name is kept available until at least igraph 0.11.

Significantly improved performance for igraph_matrix_transpose().
Documentation improvements.

igraph_distances_cutoff() and igraph_distances_dijkstra_cutoff() calculate shortest paths with an upper limit on the path length (experimental functions).
igraph_distances_floyd_warshall() for computing all-pairs shortest path lengths in dense graphs (experimental function).
igraph_ecc() computes the edge clustering coefficient of some edges (experimental function).
igraph_voronoi() computes a Voronoi partitioning of vertices (experimental function).
igraph_count_multiple_1() determines the multiplicity of a single edge in the graph.
igraph_dqueue_get() accesses an element in a queue by index.
igraph_degree_1() efficiently retrieves the degee of a single vertex.
igraph_lazy_adjlist_has() and igraph_lazy_inclist_has() to check if adjacent vertices / incident edges have already been computed and stored for a given vertex in a lazy adjlist / inclist.

igraph_edge() now verifies that the input edge ID is valid.
igraph_community_leading_eigenvector(), igraph_adjacency_spectral_embedding(), igraph_laplacian_spectral_embedding(), igraph_arpack_rssolve() and igraph_arpack_rnsolve() now generate a random starting vector using igraph's own RNG if needed instead of relying on LAPACK or ARPACK to do so. This makes sure that the results obtained from these functions remain the same if igraph's RNG is seeded with the same value.
igraph_community_leading_eigenvector() does not stop the splitting process any more when there are multiple equally likely splits (indicated by the multiplicity of the leading eigenvector being larger than 1). The algorithm picks an arbitrary split instead and proceeds normally.

Fixed a bug in igraph_get_k_shortest_paths() that sometimes yielded incorrect results on undirected graphs when the mode argument was set to IGRAPH_OUT or IGRAPH_IN.
igraph_trussness() is now interruptible.
igraph_spanner() is now interruptible.
igraph_layout_umap() and igraph_layout_umap3d() are now interruptible.
In some rare cases, roundoff errors would cause igraph_distance_johnson() to fail on graphs with negative weights.
igraph_eulerian_cycle() and igraph_eulerian_path() now returns a more specific error code (IGRAPH_ENOSOL) when the graph contains no Eulerian cycle or path.
igraph_heap_init_array() did not copy the array data correctly for non-real specializations.
igraph_layout_umap_3d() now actually uses three dimensions.
igraph_layout_umap() and igraph_layout_umap_3d() are now interruptible.
igraph_vit_create() and igraph_eit_create() no longer fails when trying to create an iterator for the null graph or edgeless graph from an empty range-based vertex or edge selector.
igraph_write_graph_leda() did not correctly print attribute names in some warning messages.
Addressed new warnings introduced by Clang 15.
In the generated pkg-config file, libxml2 is now placed in the Requires.private section instead of the Libs.private one.

Removed unused and undocumented igraph_bfgs() function.
Removed the undocumented function igraph_complex_mod(). Use igraph_complex_abs() instead, as it has identical functionality.

The IGRAPH_EDRL error code was deprecated; the DrL algorithm now returns IGRAPH_FAILURE when it used to return IGRAPH_EDRL (not likely to happen in practice).
The undocumented function igraph_dqueue_e() is now deprecated and replaced by igraph_dqueue_get().
igraph_finite(), igraph_is_nan(), igraph_is_inf(), igraph_is_posinf() and igraph_is_neginf() are now deprecated. They were relics from a time when no standard alternatives existed. Use the C99 standard isfinite(), isnan() and isinf() instead.

Documentation improvements.

Corrected a regression (compared to igraph 0.9) in weighted clique search functions.
igraph_girth() no longer fails when the graph has no cycles and the girth parameter is set to NULL.
igraph_write_graph_gml() did not respect entity encoding options when writing the Creator line.
Fixed potential memory leak on out-of-memory condition in igraph_asymmetric_preference_game(), igraph_vs_copy() and igraph_es_copy().
Fixed an assertion failure in igraph_barabasi_game() and igraph_barabasi_aging_game() when passing in negative degree exponents.
Fixed a compilation failure with some old Clang versions.

igraph_write_graph_leda() can now write boolean attributes.

Support for ARM64 on Windows.
Documentation improvements.

This release focuses on infrastructural improvements, stability, and making the igraph interface more consistent, more predictable and easier to use. It contains many API-breaking changes and function renamings, in preparation for a future 1.0 release, at which point the API will become stable. Changes in this direction are likely to continue through a 0.11 release. It is recommended that you migrate your code from 0.9 to 0.10 soon, to make the eventual transition to 1.0 easier.

Some of the highlights are:

A consistent use of igraph_integer_t for all indices and most integer quantities, both in the API and internally. This type is 64-bit by default on all 64-bit systems, bringing support for very large graphs with more than 2 billion vertices. Previously, vertex and edge indices were often represented as igraph_real_t. The move to an igraph_integer_t also implies a change from igraph_vector_t to igraph_vector_int_t in many functions.
The random number generation framework has been overhauled. Sampling from the full range of igraph_integer_t is now possible. Similarly, the sampling of random reals has been improved to utilize almost the full range of the mantissa of an igraph_real_t.
There is a new fully memory-managed container type for lists of vectors (igraph_vector_list_t), replacing most previous uses of the non-managed igraph_vector_ptr_t. Functions that previously used igraph_vector_ptr_t to return results and relied on the user to manage memory appropriately are now using igraph_vector_list_t, igraph_graph_list_t or similar and manage memory on their own.
Some simple graph properties, such as whether a graph contains self-loops or multi-edges, or whether it is connected, are now cached in the graph data structure. Querying these properties for a second time will take constant computational time. The igraph_invalidate_cache() function is provided for debugging purposes. It will invaidate all cache entries.
File format readers are much more robust and more tolerant of invalid input.
igraph is much more resilient to overflow errors.
Many improvements to robustness and reliability, made possible by internal refactorings.

igraph now requires CMake 3.18 or later.
In order to facilitate the usage of graphs with more than 2 billion vertices and edges, we have made the size of the igraph_integer_t data type to be 32 bits on 32-bit platforms and 64 bits on 64-bit platforms by default. You also have the option to compile a 32-bit igraph variant on a 64-bit platform by changing the IGRAPH_INTEGER_SIZE build variable in CMake to 32.
igraph_bool_t is now a C99 bool and not an int. Similarly, igraph_vector_bool_t now consumes sizeof(bool) bytes per entry only, not sizeof(int). The standard constants true and false may be used for Boolean values for readability.
The random number generator interface, igraph_rng_type_t, has been overhauled. Check the declaration of the type for details.
The default random number generator has been changed from Mersenne Twister to PCG32.
Functions related to spectral coarse graining (i.e. all functions starting with igraph_scg_...) were separated into a project of its own. If you wish to keep on using these functions, please refer to the repository hosting the spectral coarse graining code at https://github.com/igraph/igraph-scg . The spectral coarse graining code was updated to support igraph 0.10.
Since igraph_integer_t aims to be the largest integer size that is feasible on a particular platform, there is no need for generic data types based on long int anymore. The long variants of generic data types (e.g., igraph_vector_long_t) are therefore removed; you should use the corresponding int variant instead, whose elements are of type igraph_integer_t.
Generic data types based on float were removed as they were not used anywhere in the library.
Several igraph functions that used to take a long int or return a long int now takes or returns an igraph_integer_t instead to make the APIs more consistent. Similarly, igraph functions that used igraph_vector_t for arguments that take or return integral vectors (e.g., vertex or edge indices) now take igraph_vector_int_t instead. Graph-related functions where the API was changed due to this reason are listed below, one by one.
Similarly, igraph functions that used to accept the long variant of a generic igraph data type (e.g., igraph_vector_long_t) now take the int variant of the same data type.
The type igraph_stack_ptr_t and its associated functions were removed. Use igraph_vector_ptr_t and associated functions instead.
Error handlers should no longer perform a longjmp(). Doing so will introduce memory leaks, as resource cleanup is now done in multiple stages, through multiple calls to the error handler. Thus, the error handler should either abort execution immediately (as the default handler does), or report the error, call IGRAPH_FINALLY_FREE(), and return normally.
Most callback functions now return an error code. In previous versions they returned a boolean value indicating whether to terminate the search. A request to stop the search is now indicated with the special return code IGRAPH_STOP.
igraph_add_edges() now uses an igraph_vector_int_t for its edges parameter.
igraph_adjacency() no longer accepts a negative number of edges in its adjacency matrix. When negative entries are found, an error is generated.
igraph_adjacency() gained an additional loops argument that lets you specify whether the diagonal entries should be ignored or should be interpreted as raw edge counts or twice the number of edges (which is common in linear algebra contexts).
igraph_all_minimal_st_separators() now returns the separators in an igraph_vector_int_list_t containing igraph_vector_int_t vectors.
igraph_all_st_cuts() and igraph_all_st_mincuts() now return the cuts in an igraph_vector_int_list_t containing igraph_vector_int_t vectors.
igraph_arpack_unpack_complex() now uses igraph_integer_t for its nev argument instead of long int.
igraph_articulation_points() now uses an igraph_vector_int_t to return the list of articulation points, not an igraph_vector_t.
igraph_assortativity_nominal() now accepts vertex types in an igraph_vector_int_t instead of an igraph_vector_t.
igraph_asymmetric_preferennce_game() now uses an igraph_vector_int_t to return the types of the nodes in the generated graph.
igraph_atlas() now uses igraph_integer_t for its number argument.
igraph_automorphism_group() now returns the generators in an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
igraph_barabasi_game(), igraph_barabasi_aging_game(), igraph_recent_degree_game() and igraph_recent_degree_aging_game() now use an igraph_vector_int_t for the out-degree sequence of the nodes being generated instead of an igraph_vector_t.
igraph_bfs() now takes an igraph_vector_int_t for its roots, restricted, order, father, pred, succ and dist arguments instead of an igraph_vector_t.
igraph_bfs_simple() now takes igraph_vector_int_t for its vids, layers and parents arguments instead of an igraph_vector_t.
igraph_bfs_simple() now returns -1 in parents for the root node of the traversal, and -2 for unreachable vertices. This is now consistent with other functions that return a parent vector.
igraph_biconnected_components() now uses an igraph_vector_int_t to return the list of articulation points, not an igraph_vector_t. Also, the container used for the edges and vertices of the components is now an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
igraph_bipartite_projection() now uses igraph_vector_int_t to return multiplicity1 and multiplicity2, not igraph_vector_t.
igraph_bridges() now uses an igraph_vector_int_t to return the list of bridges, not an igraph_vector_t.
igraph_callaway_traits_game() returns the node types in an igraph_vector_int_t instead of an igraph_vector_t.
igraph_canonical_permutation() now uses an igraph_vector_int_t for its labeling parameter.
igraph_cattribute_list() now uses igraph_vector_int_t to return gtypes, vtypes and etypes.
igraph_cited_type_game() now uses an igraph_vector_int_t for its types parameter.
igraph_citing_cited_type_game() now uses an igraph_vector_int_t for its types parameter.
igraph_clique_handler_t now uses an igraph_vector_int_t for its clique parameter, and must return an igraph_error_t. Use IGRAPH_STOP as the return code to terminate the search prematurely. The vector that the handler receives is owned by the clique search routine. If you want to hold on to the vector for a longer period of time, you need to make a copy of it in the handler. Cliques passed to the callback are marked as const as a reminder to this change.
The res parameter of igraph_cliques() is now an igraph_vector_int_list_t.
Callbacks used by igraph_cliques_callback() need to be updated to account for the fact that the callback does not own the clique passed to it any more; the callback needs to make a copy if it wants to hold on to the clique for a longer period of time. If the callback does not need to store the clique, it does not need to do anything any more, and it must not destroy or free the clique.
igraph_closeness() and igraph_closeness_cutoff() now use an igraph_vector_int_t to return reachable_count, not an igraph_vector_t.
igraph_cohesive_blocks() now uses an igraph_vector_int_t to return the mapping from block indices to parent block indices, and the cohesion; also, it uses an igraph_vector_int_list_t to return the blocks themselves instead of a pointer vector of igraph_vector_t.
The igraph_community_eb_get_merges() bridges parameter now starts the indices into the edge removal vector at 0, not 1.
The igraph_community_eb_get_merges() now reports an error when not all edges in the graph are removed, instead of a nonsensical result.
igraph_community_edge_betweenness() now uses an igraph_vector_int_t to return the edge IDs in the order of their removal as well as the list of edge IDs whose removal broke a single component into two.
igraph_community_fluid_communities() does not provide the modularity in a separate output argument any more; use igraph_modularity() to retrieve the modularity if you need it.
igraph_community_infomap() now uses igraph_integer_t for its nb_trials argument.
igraph_community_label_propagation() now uses an igraph_vector_int_t for its initial parameter. It also takes a mode argument that specifies how labels should be propagated along edges (forward, backward or ignoring edge directions).
igraph_community_label_propagation() does not provide the modularity in a separate output argument any more; use igraph_modularity() to retrieve the modularity if you need it.
igraph_community_leiden() has an additional parameter to indicate the number of iterations to perform (PR #2177).
igraph_community_walktrap(), igraph_community_edge_betweenness(), igraph_community_eb_get_merges(), igraph_community_fastgreedy(), igraph_community_to_membership(), igraph_le_community_to_membership(), igraph_community_leading_eigenvector() now use an igraph_vector_int_t for their merges parameter.
igraph_community_walktrap() now uses igraph_integer_t for its steps argument.
igraph_coreness() now uses an igraph_vector_int_t to return the coreness values.
igraph_convex_hull() now uses an igraph_vector_int_t to return the indices of the input vertices that were chosen to be in the convex hull.
igraph_correlated_game() and igraph_correlated_pair_game() now take an igraph_vector_int_t as the permutation vector, not an igraph_vector_t.
igraph_create() now uses an igraph_vector_int_t for its edges parameter.
igraph_create_bipartite() now uses an igraph_vector_int_t for its edges parameter.
igraph_compose() now returns the edge maps in an igraph_vector_int_t instead of an igraph_vector_t.
igraph_count_multiple() now returns the multiplicities in an igraph_vector_int_t instead of an igraph_vector_t.
igraph_decompose() now uses an igraph_integer_t for its maxcompno and minelements arguments instead of a long int.
igraph_degree() now uses an igraph_vector_int_t to return the degrees. If you need the degrees in a vector containing floating-point numbers instead (e.g., because you want to pass them on to some other function that takes an igraph_vector_t), use igraph_strength() instead with a null weight vector.
igraph_degree_sequence_game() now takes degree sequences represented as igraph_vector_int_t instead of igraph_vector_t.
igraph_degseq_t, used by igraph_degree_sequence_game(), uses new names for its constants. The old names are deprecated, but retained for compatibility. See igraph_constants.h to see which new name corresponds to which old one.
igraph_delete_vertices_idx() now uses igraph_vector_int_t vectors to return the mapping and the inverse mapping of old vertex IDs to new ones.
igraph_deterministic_optimal_imitation() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
igraph_dfs() now takes an igraph_vector_int_t for its order, order_out, father and dist arguments instead of an igraph_vector_t. Furthermore, these vectors will contain -2 for vertices that have not been visited; in earlier versions, they used to contain NaN instead. Note that -1 is still used in the father vector to indicate the root of a DFS tree.
igraph_diameter() and igraph_diameter_dijkstra() now use igraph_vector_int_t vectors to return the list of vertex and edge IDs in the diameter.
igraph_dominator_tree() now takes an igraph_vector_int_t for its dom and leftout arguments instead of an igraph_vector_t.
igraph_dyad_census() now uses igraph_real_t instead of igraph_integer_t for its output arguments, and it no longer returns -1 when overflow occurs.
igraph_edges() now takes an igraph_vector_int_t for its edges argument instead of an igraph_vector_t.
igraph_es_multipairs() was removed; you can use the newly added igraph_es_all_between() instead.
igraph_establishment_game() now takes an igraph_vector_int_t for its node_type_vec argument instead of an igraph_vector_t.
igraph_eulerian_path() and igraph_eulerian_cycle() now use igraph_vector_int_t to return the list of edge and vertex IDs participating in an Eulerian path or cycle instead of an igraph_vector_t.
igraph_feedback_arc_set() now uses an igraph_vector_int_t to return the IDs of the edges in the feedback arc set instead of an igraph_vector_t.
igraph_get_adjacency() no longer has the eids argument, which would produce an adjacency matrix where non-zero values were 1-based (not 0-based) edge IDs. If you need a matrix with edge IDs, create it manually.
igraph_get_adjacency_sparse() now returns the sparse adjacency matrix in an igraph_sparsemat_t structure, and it assumes that the input matrix is initialized for sake of consistency with other igraph functions.
igraph_get_adjacency() and igraph_get_adjacency_sparse() now has a loops argument that lets the user specify how loop edges should be handled.
igraph_get_edgelist() now uses an igraph_vector_int_t for its res parameter.
igraph_get_eids() now uses igraph_vector_int_t to return lists of edge IDs and to receive lists of vertex IDs.
The path argument of igraph_get_eids() was removed. You can replicate the old behaviour by constructing the list of vertex IDs explicitly from the path by duplicating each vertex in the path except the first and last ones. A helper function called igraph_expand_path_to_pairs() is provided to ease the transition.
igraph_get_eids_multi() was removed as its design was fundamentally broken; there was no way to retrieve the IDs of all edges between a specific pair of vertices without knowing in advance how many such edges there are in the graph. Use igraph_get_all_eids_between() instead.
igraph_get_incidence() now returns the vertex IDs corresponding to the rows and columns of the incidence matrix as igraph_vector_int_t.
igraph_get_shortest_path(), igraph_get_shortest_path_bellman_ford() and igraph_get_shortest_path_dijkstra() now use igraph_vector_int_t vectors to return the list of vertex and edge IDs in the shortest path.
igraph_get_shortest_paths(), igraph_get_shortest_paths_dijkstra() and igraph_get_shortest_paths_bellman_ford() now use an igraph_vector_int_t to return the predecessors and inbound edges instead of an igraph_vector_long_t.
The functions igraph_get_all_shortest_paths(), igraph_get_all_shortest_paths_dijkstra(), igraph_get_shortest_paths(), igraph_get_shortest_paths_bellman_ford() and igraph_get_shortest_paths_dijkstra() now return paths in an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
The vector of parents in igraph_get_shortest_paths(), igraph_get_shortest_paths_bellman_ford() and igraph_get_shortest_paths_dijkstra() now use -1 to represent the starting vertex, and -2 for unreachable vertices.
The maps parameters in igraph_get_isomorphisms_vf2() and igraph_get_subisomorphisms_vf2() are now of type igraph_vector_int_list_t.
igraph_get_stochastic() now has an additional weights argument for edge weights.
igraph_get_stochastic_sparse() now returns the sparse adjacency matrix in an igraph_sparsemat_t structure, and it assumes that the input matrix is initialized for sake of consistency with other igraph functions. It also received an additional weights argument for edge weights.
igraph_girth() now uses an igraph_vector_int_t for its circle parameter.
igraph_girth() now uses igraph_real_t as the return value so we can return infinity for graphs with no cycles (instead of zero).
The cliques parameters of type igraph_vector_ptr_t in igraph_graphlets(), igraph_graphlets_candidate_basis() and igraph_graphlets_project() were changed to an igraph_vector_int_list_t.
igraph_hrg_init() and igraph_hrg_resize() now takes an igraph_integer_t as their size arguments instead of an int.
igraph_hrg_consensus() now returns the parent vector in an igraph_vector_int_t instead of an igraph_vector_t.
igraph_hrg_create() now takes a vector of probabilities corresponding to the internal nodes of the dendogram. It used to also take probabilities for the leaf nodes and then ignore them.
igraph_hrg_predict() now uses an igraph_vector_int_t for its edges parameter.
igraph_hrg_sample() now always samples a single graph only. Use igraph_hrg_sample_many() if you need more than one sample, and call igraph_hrg_fit() beforehand if you do not have a HRG model but only a single input graph.
igraph_hrg_size() now returns an igraph_integer_t instead of an int.
igraph_incidence() does not accept negative incidence counts any more.
igraph_incident() now uses an igraph_vector_int_t for its eids parameter.
The res parameter in igraph_independent_vertex_sets() is now an igraph_vector_int_list_t.
igraph_induced_subgraph_map() now uses igraph_vector_int_t vectors to return the mapping and the inverse mapping of old vertex IDs to new ones.
igraph_intersection() now uses an igraph_vector_int_t for its edge_map1 and edge_map2 parameters.
The edgemaps parameter of igraph_intersection_many() is now an igraph_vector_int_list_t instead of a pointer vector.
igraph_is_chordal() now uses an igraph_vector_int_t for its alpha, alpham1 and fill_in parameters.
igraph_is_graphical() and igraph_is_bigraphical() now take degree sequences represented as igraph_vector_int_t instead of igraph_vector_t.
igraph_is_matching(), igraph_is_maximal_matching() and igraph_maximum_bipartite_matching now use an igraph_vector_int_t to return the matching instead of an igraph_vector_long_t.
igraph_is_mutual() has an additional parameter which controls whether directed self-loops are considered mutual.
The vids parameter for igraph_isoclass_subgraph() is now an igraph_vector_int_t instead of igraph_vector_t.
igraph_isomorphic_vf2(), igraph_get_isomorphisms_vf2_callback() (which used to be called igraph_isomorphic_function_vf2()) and igraph_isohandler_t now all use igraph_vector_int_t for their map12 and map21 parameters.
The cliques parameter of type igraph_vector_ptr_t in igraph_largest_cliques() was changed to an igraph_vector_int_list_t.
The res parameters of type igraph_vector_ptr_t in igraph_largest_independent_vertex_sets() and igraph_largest_weighted_cliques() were changed to an igraph_vector_int_list_t.
The dimension vector parameter for igraph_square_lattice() (used to be igraph_lattice()) is now an igraph_vector_int_t instead of igraph_vector_t.
The maxiter parameter of igraph_layout_bipartite() is now an igraph_integer_t instead of long int.
The fixed parameter of igraph_layout_drl() and igraph_layout_drl_3d() was removed as it has never been implemented properly.
The width parameter of igraph_layout_grid() is now an igraph_integer_t instead of long int.
The width and height parameters of igraph_layout_grid_3d() are now igraph_integer_t instead of long int.
The dimension parameter of igraph_layout_mds() is now an igraph_integer_t instead of long int.
The roots and rootlevel parameters of igraph_layout_reingold_tilford() are now igraph_vector_int_t instead of igraph_vector_t.
The roots and rootlevel parameters of igraph_layout_reingold_tilford_circular() are now igraph_vector_int_t instead of igraph_vector_t.
The order parameter of igraph_layout_star() is now an igraph_vector_int_t instead of an igraph_vector_t.
The maxiter parameter of igraph_layout_sugiyama() is now an igraph_integer_t instead of long int. Also, the function now uses an igraph_vector_int_t for its extd_to_orig_eids parameter.
The shifts parameter of igraph_lcf_vector() is now an igraph_vector_int_t instead of an igraph_vector_t.
igraph_matrix_minmax(), igraph_matrix_which_minmax(), igraph_matrix_which_min() and igraph_matrix_which_max() no longer return an error code. The return type is now void. These functions never fail.
igraph_maxflow() now uses an igraph_vector_int_t for its cut, partition and partition2 parameters.
The igraph_maxflow_stats_t struct now contains igraph_integer_t values instead of int ones.
The res parameters in igraph_maximal_cliques() and igraph_maximal_cliques_subset() are now of type igraph_vector_int_list_t.
Callbacks used by igraph_maximal_cliques_callback() need to be updated to account for the fact that the callback does not own the clique passed to it any more; the callback needs to make a copy if it wants to hold on to the clique for a longer period of time. If the callback does not need to store the clique, it does not need to do anything any more, and it must not destroy or free the clique.
The res parameter in igraph_maximal_independent_vertex_sets() is now an igraph_vector_int_list_t.
igraph_maximum_cardinality_search() now uses an igraph_vector_int_t for its alpha and alpham1 arguments.
igraph_mincut() now uses an igraph_vector_int_t for its cut, partition and partition2 parameters.
igraph_moran_process() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
Motif callbacks of type igraph_motifs_handler_t now take an igraph_vector_int_t with the vertex IDs instead of an igraph_vector_t, and use igraph_integer_t for the isoclass parameter.
Motif functions now use igraph_integer_t instead of int for their size parameter.
igraph_neighborhood_size() now uses an igraph_vector_int_t for its res parameter.
The res parameter of igraph_neighborhood() is now an igraph_vector_int_list_t.
igraph_neighbors() now uses an igraph_vector_int_t for its neis parameter.
igraph_permute_vertices() now takes an igraph_vector_int_t as the permutation vector.
igraph_power_law_fit() does not calculate the p-value automatically any more because the previous estimation method did not match the results from the original paper of Clauset, Shalizi and Newman (2009) and the implementation of the method outlined in the paper runs slower than the previous naive estimate. A separate function named igraph_plfit_result_calculate_p_value() is now provided for calculating the p-value. The automatic selection of the x_min cutoff also uses a different method than earlier versions. As a consequence, results might be slightly different if you used tests where the x_min cutoff was selected automatically. The new behaviour is now consistent with the defaults of the underlying plfit library.
igraph_preference_game() now uses an igraph_vector_int_t to return the types of the nodes in the generated graph.
igraph_random_walk() now uses an igraph_vector_int_t for its results. Also, the function now takes both vertices and edges as parameters. It can return IDs of vertices and/or edges on the walk. The function now takes weights as a parameter to support weighted graphs.
igraph_random_edge_walk() now uses an igraph_vector_int_t for its edgewalk parameter.
igraph_read_graph_dimacs_flow() now uses an igraph_vector_int_t for its label parameter.
igraph_read_graph_graphml() now uses igraph_integer_t for its index argument.
igraph_read_graph_pajek() now creates a Boolean type attribute for bipartite graphs. Previously it created a numeric attribute.
igraph_realize_degree_sequence() now uses an igraph_vector_int_t for its outdeg and indeg parameters.
igraph_reindex_membership() now uses an igraph_vector_int_t for its new_to_old parameter.
igraph_rng_seed() now requires an igraph_uint_t as its seed arguments. RNG implementations are free to use only the lower bits of the seed if they do not support 64-bit seeds.
igraph_rngtype_rand (i.e. the RNG that is based on BSD rand()) was removed due to poor statistical properties that sometimes resulted in weird artifacts like all-even "random" numbers when igraph's usage patterns happened to line up with the shortcomings of the rand() generator in a certain way.
igraph_roulette_wheel_imitation() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
igraph_similarity_dice_pairs() now uses an igraph_vector_int_t for its pairs parameter.
igraph_similarity_jaccard_pairs() now uses an igraph_vector_int_t for its pairs parameter.
igraph_simple_interconnected_islands_game() does not generate multi-edges between islands any more.
igraph_sort_vertex_ids_by_degree() and igraph_topological_sorting() now use an igraph_vector_int_t to return the vertex IDs instead of an igraph_vector_t.
igraph_spanning_tree(), igraph_minimum_spanning_tree() and igraph_random_spanning_tree() now all use an igraph_vector_int_t to return the vector of edge IDs in the spanning tree instead of an igraph_vector_t.
igraph_sparsemat_cholsol(), igraph_sparsemat_lusol(), igraph_sparsemat_symbqr() and igraph_sparsemat_symblu() now take an igraph_integer_t as their order parameter.
igraph_sparsemat_count_nonzero() and igraph_sparsemat_count_nonzerotol() now return an igraph_integer_t.
igraph_sparsemat_is_symmetric() now returns an error code and the result itself is provided in an output argument.
The values argument of igraph_sparsemat_transpose() was removed; now the function always copies the values over to the transposed matrix.
igraph_spmatrix_t and related functions were removed as they mostly duplicated functionality that was already present in igraph_sparsemat_t. Functions that used igraph_spmatrix_t in the library now use igraph_sparsemat_t.
igraph_stochastic_imitation() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
igraph_st_mincut() now uses an igraph_vector_int_t for its cut, partition and partition2 parameters.
igraph_st_vertex_connectivity() now ignores edges between source and target for IGRAPH_VCONN_NEI_IGNORE
igraph_strvector_get() now returns strings in the return value, not in an output argument.
igraph_subcomponent() now uses an igraph_integer_t for the seed vertex instead of an igraph_real_t. It also uses an igraph_vector_int_t to return the list of vertices in the same component as the seed vertex instead of an igraph_vector_t.
igraph_subisomorphic_vf2(), igraph_get_subisomorphisms_vf2_callback() (which used to be called igraph_subisomorphic_function_vf2()) and igraph_isomorphic_bliss() now all use igraph_vector_int_t for their map12 and map21 parameters.
The maps parameters in igraph_subisomorphic_lad(), igraph_get_isomorphisms_vf2() and igraph_get_subisomorphisms_vf2() are now of type igraph_vector_int_list_t.
igraph_subisomorphic_lad() now uses an igraph_vector_int_t for its map parameter. Also, its domains parameter is now an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
igraph_unfold_tree() now uses an igraph_vector_int_t for its vertex_index and roots parameters.
igraph_union() now uses an igraph_vector_int_t for its edge_map1 and edge_map2 parameters.
The edgemaps parameter of igraph_union_many() is now an igraph_vector_int_list_t instead of a pointer vector.
igraph_vector_init_copy() was refactored to take another vector that the newly initialized vector should copy. The old array-based initialization function is now called igraph_vector_init_array().
igraph_vector_ptr_init_copy() was renamed to igraph_vector_ptr_init_array() for sake of consistency.
igraph_vs_vector(), igraph_vss_vector() and igraph_vs_vector_copy() now all take an igraph_vector_int_t as the vector of vertex IDs, not an igraph_vector_t. Similarly, igraph_vs_as_vector() now returns the vector of matched vertex IDs in an igraph_vector_int_t, not an igraph_vector_t.
The res parameter of igraph_weighted_cliques() is now an igraph_vector_int_list_t.
igraph_write_graph_dimacs_flow() now uses igraph_integer_t for the source and target vertex index instead of a long int.
igraph_vector_*(), igraph_matrix_*(), igraph_stack_*(), igraph_array_*() and several other generic igraph data types now use igraph_integer_t for indexing, not long int. Please refer to the headers for the exact details; the list of affected functions is too large to include here.
igraph_vector_minmax() and igraph_vector_which_minmax() no longer return an error code. The return type is now void. These functions never fail.
igraph_vector_order() was removed; use igraph_vector_int_pair_order() instead. (The original function worked for vectors containing integers only).
igraph_vector_resize_min() and igraph_matrix_resize_min() no longer return an error code (return type is now void). The vector or matrix is always left in a consistent state by these functions, with all data intact, even if releasing unused storage is not successful.
igraph_vector_qsort_ind() and its variants now take an igraph_order_t enum instead of a boolean to denote whether the order should be ascending or descending.
igraph_weighted_adjacency() now returns the weights in a separate vector instead of storing it in a vertex attribute. The reason is twofold: first, the previous solution worked only with the C attribute handler (not the ones from the higher-level interfaces), and second, it wasn't consistent with other igraph functions that use weights provided as separate arguments.
The loops argument of igraph_weighted_adjacency() was converted to an igraph_loops_t for sake of consistency with igraph_adjacency() and igraph_get_adjacency().
igraph_write_graph_gml() takes an additional bitfield parameter controlling some aspects of writing the GML file.
The add_edges() function in the attribute handler now takes an igraph_vector_int_t for its edges parameter instead of an igraph_vector_t. The add_vertices() function now takes an igraph_integer_t for the vertex count instead of a long int. The combine_vertices() and combine_edges() functions now take an igraph_vector_ptr_t containing vectors of type igraph_vector_int_t in their merges parameters. The get_info() function now uses igraph_vector_int_t to return the types of the graph, vertex and edge attribute types. The permute_vertices() and permute_edges() functions in the attribute handler tables now take an igraph_vector_int_t instead of an igraph_vector_t for the index vectors. These are relevant only to maintainers of higher level interfaces to igraph; they should update their attribute handlers accordingly.
igraph functions that interface with external libraries such as BLAS or LAPACK may now fail if the underlying BLAS or LAPACK implementation cannot handle the size of input vectors or matrices (BLAS and LAPACK are usually limited to vectors whose size fits in an int). igraph_blas_dgemv() and igraph_blas_dgemv_array() thus now return an igraph_error_t, which may be set to IGRAPH_EOVERFLOW if the input vectors or matrices are too large.
Functions that used an igraph_vector_t to represent cluster size and cluster membership now use an igraph_vector_int_t instead. These are:
igraph_connected_components() (used to be igraph_clusters() in 0.9 and before)
igraph_community_eb_get_merges()
igraph_community_edge_betweenness()
igraph_community_fastgreedy()
igraph_community_fluid_communities()
igraph_community_infomap()
igraph_community_label_propagation()
igraph_community_leading_eigenvector()
igraph_community_leiden()
igraph_community_multilevel()
igraph_community_optimal_modularity()
igraph_community_spinglass()
igraph_community_spinglass_single()
igraph_community_to_membership()
igraph_community_walktrap()
igraph_compare_communities()
igraph_le_community_to_membership()
igraph_modularity()
igraph_reindex_membership()
igraph_split_join_distance()
igraph_community_multilevel() additionally uses a igraph_matrix_int_t instead of igraph_matrix_t() for its memberships parameter.
IGRAPH_TOTAL was removed from the igraph_neimode_t enum; use the equivalent IGRAPH_ALL instead.

A new integer type, igraph_uint_t has been added. This is the unsigned pair of igraph_integer_t and they are always consistent in size.
A new container type, igraph_vector_list_t has been added, replacing most uses of igraph_vector_ptr_t in the API where it was used to hold a variable-length list of vectors. The type contains igraph_vector_t objects, and it is fully memory managed (i.e. its contents do not need to be allocated and destroyed manually). There is also a variant named igraph_vector_int_list_t for vectors of igraph_vector_int_t objects.
A new container type, igraph_matrix_list_t has been added, replacing most uses of igraph_vector_ptr_t in the API where it was used to hold a variable-length list of matrices. The type contains igraph_matrix_t objects, and it is fully memory managed (i.e. its contents do not need to be allocated and destroyed manually).
A new container type, igraph_graph_list_t has been added, replacing most uses of igraph_vector_ptr_t in the API where it was used to hold a variable-length list of graphs. The type contains igraph_t objects, and it is fully memory managed (i.e. its contents do not need to be allocated and destroyed manually).
The vector container type, igraph_vector_t, has been extended with a new variant whose functions all start with igraph_vector_fortran_int_.... This vector container can be used for interfacing with Fortran code as it guarantees that the integers in the vector are compatible with Fortran integers. Note that igraph_vector_int_t is not suitable any more, as the elements of igraph_vector_int_t are of type igraph_integer_t, whose size may differ on 32-bit and 64-bit platforms, depending on how igraph was compiled.
igraph_adjlist_init_from_inclist() to create an adjacency list from an already existing incidence list by resolving edge IDs to their corresponding endpoints. This function is useful for algorithms when both an adjacency and an incidence list is needed and they should be in the same order.
igraph_almost_equals() and igraph_cmp_epsilon() to compare floating point numbers with a relative tolerance.
igraph_betweenness_subset() and igraph_edge_betweenness_subset() calculates betweenness and edge betweenness scores using shortest paths between a subset of vertices only (#1711, thanks to @guyroznb)
igraph_blas_dgemm() to multiply two matrices.
igraph_calloc() and igraph_realloc() are now publicly exposed; these functions provide variants of calloc() and realloc() that can safely be deallocated within igraph functions.
igraph_circulant() to create circulant graphs (#1856, thanks to @Gomango999).
igraph_complex_almost_equals() to compare complex numbers with a relative tolerance.
igraph_eccentricity_dijkstra() finds the longest weighted path length among all shortest paths between a set of vertices.
igraph_enter_safelocale() and igraph_exit_safelocale() for temporarily setting the locale to C. Foreign format readers and writers require a locale which uses a decimal point instead of decimal comma.
igraph_es_all_between() to create an edge selector that selects all edges between a pair of vertices.
igraph_full_multipartite() generates full multipartite graphs (a generalization of bipartite graphs to multiple groups).
igraph_fundamental_cycles() computes a fundamental cycle basis (experimental).
igraph_generalized_petersen() to create generalized Petersen graphs (#1844, thanks to @alexsyou).
igraph_get_all_eids_between() returns the IDs of all edges between a pair of vertices.
igraph_get_k_shortest_paths() finds the k shortest paths between a source and a target vertex.
igraph_get_laplacian() and igraph_get_laplacian_sparse() return the Laplacian matrix of the graph as a dense or sparse matrix, with various kinds of normalizations. They replace the now-deprecated igraph_laplacian() function. This makes the API consistent with igraph_get_adjacency() and igraph_get_adjacency_sparse().
igraph_get_widest_path(), igraph_get_widest_paths(), igraph_widest_path_widths_dijkstra() and igraph_widest_path_widths_floyd_warshall() to find widest paths (#1893, thanks to @Gomango999).
igraph_graph_center() finds the central vertices of the graph. The central vertices are the ones having a minimum eccentricity (PR #2084, thanks to @pradkrish).
igraph_graph_count() returns the number of unlabelled graphs on a given number of vertices. It is meant to find the maximum isoclass value.
igraph_has_mutual() checks if a directed graph has any mutual edges.
igraph_heap_clear() and igraph_heap_min_clear() remove all elements from an igraph_heap_t or an igraph_heap_min_t, respectively.
igraph_invalidate_cache() invalidates all cached graph properties, forcing their recomputation next time they are requested. This function should not be needed in everyday usage, but may be useful in debugging and benchmarking.
igraph_is_forest() to check whether a graph is a forest (#1888, thanks to @rohitt28).
igraph_is_acyclic() to check whether a graph is acyclic (#1945, thanks to @borsgeorgica).
igraph_is_perfect() to check whether a graph is a perfect graph (#1730, thanks to @guyroznb).
igraph_hub_and_authority_scores() calculates the hub and authority scores of a graph as a matching pair.
igraph_layout_umap() and igraph_layout_umap_3d() to lay out a graph in 2D or 3D space using the UMAP dimensionality reduction algorithm.
igraph_local_scan_subset_ecount() counts the number of edges in induced sugraphs from a subset of vertices.
igraph_matrix_view_from_vector() allows interpreting the data stored in a vector as a matrix of the specified size.
igraph_minimum_cycle_basis() computes an unweighted minimum cycle basis (experimental).
igraph_pseudo_diameter() and igraph_pseudo_diameter_dijkstra() to determine a lower bound for the diameter of a graph (unweighted or weighted).
igraph_regular_tree() creates a regular tree where all internal vertices have the same total degree.
igraph_rngtype_pcg32 and igraph_rngtype_pcg64 implement 32-bit and 64-bit variants of the PCG random number generator.
igraph_rng_get_pois() generates random variates from the Poisson distribution.
igraph_roots_for_tree_layout() computes a set of roots suitable for a nice tree layout.
igraph_spanner() calculates a spanner of a graph with a given stretch factor (#1752, thanks to @guyroznb)
igraph_sparse_adjacency() and igraph_sparse_weighted_adjacency() constructs graphs from (weighted) sparse matrices.
igraph_sparsemat_get() to retrieve a single element of a sparse matrix.
igraph_sparsemat_normalize_rows() and igraph_sparsemat_normalize_cols() to normalize sparse matrices row-wise or column-wise.
igraph_stack_capacity() to query the capacity of a stack.
igraph_strvector_capacity() returns the maximum number of strings that can be stored in a string vector without reallocating the memory block holding the pointers to the individual strings.
igraph_strvector_merge() moves all strings from one string vectors to the end of another without re-allocating them.
igraph_strvector_push_back_len() adds a new string to the end of a string vector and allows the user to specify the length of the string being added.
igraph_strvector_reserve() reserves space for a given number of string pointers in a string vector.
igraph_symmetric_tree() to create a tree with the specified number of branches at each level (#1859, thanks to @YuliYudith and @DoruntinaM).
igraph_trussness() calculates the trussness of each edge in the graph (#1034, thanks to @alexperrone)
igraph_turan() generates Turán graphs (#2088, thanks to @pradkrish)
igraph_vector_all_almost_e(), igraph_vector_complex_all_almost_e(), igraph_matrix_all_almost_e(), igraph_matrix_complex_all_almost_e() for elementwise comparisons of floating point vector and matrices with a relative tolerance.
igraph_vector_complex_zapsmall() and igraph_matrix_complex_zapsmall() for replacing small components of complex vector or matrix elements with exact zeros.
igraph_vector_lex_cmp_untyped() and igraph_vector_colex_cmp_untyped() for lexicographic and colexicographic comparison of vectors, similarly to igraph_vector_lex_cmp() and igraph_vector_colex_cmp(). The difference between the two variants is that the untyped versions declare the vectors as const void*, making the functions suitable as comparators for qsort().
igraph_vector_permute() functions to permute a vector based on an index vector.
igraph_vector_ptr_sort_ind() to obtain an index vector that would sort a vector of pointers based on some comparison function.
igraph_vector_range() to fill an existing vector with a range of increasing numbers.
igraph_vector_remove_fast() functions to remove an item from a vector by swapping it with the last element and then popping it off. It allows one to remove an item from a vector in constant time if the order of items does not matter.
igraph_vertex_path_from_edge_path() converts a sequence of edge IDs representing a path to an equivalent sequence of vertex IDs that represent the vertices the path travelled through.
igraph_vs_range(), igraph_vss_range(), igraph_es_range() and igraph_ess_range() creates vertex and edge sequences from C-style intervals (closed from the left, open from the right).
igraph_wheel() to create a wheel graph (#1938, thanks to @kwofach).

igraph_adjlist_remove_duplicate(), igraph_betweenness_estimate(), igraph_closeness_estimate(), igraph_edge_betweenness_estimate(), igraph_inclist_remove_duplicate(), igraph_is_degree_sequence() and igraph_is_graphical_degree_sequence() were deprecated earlier in 0.9.0 and are now removed in this release.
igraph_dnorm(), igraph_strvector_move_interval(), igraph_strvector_permdelete() and igraph_strvector_remove_negidx() were removed. These are not breaking changes as the functions were never documented, they were only exposed from one of the headers.
igraph_eigen_laplacian(), igraph_es_fromto() and igraph_maximum_matching() were removed. These are not breaking changes either as the functions were never implemented, they returned an error code unconditionally.

igraph_degree_sequence_game() now supports an additional method, IGRAPH_DEGSEQ_EDGE_SWITCHING_SIMPLE, an edge-switching MCMC sampler.
igraph_get_adjacency() and igraph_get_adjacency_sparse() now count loop edges twice in undirected graphs when using IGRAPH_GET_ADJACENCY_BOTH. This is to ensure consistency with IGRAPH_GET_ADJACENCY_UPPER and IGRAPH_GET_ADJACENCY_LOWER such that the sum of the upper and the lower triangle matrix is equal to the full adjacency matrix even in the presence of loop edges.
igraph_matrix_print() and igraph_matrix_fprint() functions now align columns when priting.
igraph_read_graph_gml() now supports graph attributes (in addition to vertex and edge attributes).
igraph_read_graph_gml() now uses NaN as the default numerical attribute values instead of 0.
The Pajek parser in igraph_read_graph_pajek() is now less strict and accepts more files.
igraph_ring() no longer simplifies its result when generating a one- or two-vertex graph. The one-cycle has a self-loop and the undirected two-cycle has parallel edges.
igraph_vector_view() now allows data to be NULL in the special case when length == 0.
igraph_version() no longer returns an error code.
igraph_write_graph_gml() uses the creator parameter in a different way: the supplied string is now written into the Creator line as-is instead of being appended to a default value.
igraph_write_graph_gml() skips writing NaN values. These two changes ensure consistent round-tripping.
igraph_write_graph_gml() and igraph_read_graph_gml() now have limited support for entity encoding.
igraph_write_graph_ncol() now preserves the edge ordering of the graph when writing an NCOL file.
igraph functions that take an ARPACK options object now also accept NULL in place of an options object, and they will fall back to using a default object provided by igraph_arpack_options_get_default().
Foreign format readers now present more informative error messages.
The default tolerance of the zapsmall functions is now eps^(2/3) instead of eps^(1/2) where eps is the machine epsilon of igraph_real_t.
It is now possible to override the uniform integer and the Poisson samplers in the random number generator interface.

When an error occurs during parsing DL, GML, NCOL, LGL or Pajek files, line numbers are now reported correctly.
The GraphML parser does not print to stderr any more in case of encoding errors and other error conditions originating from the underlying libxml2 library.
The GraphML parser would omit some edges and vertices when reading files with custom attribute types, such as those produced by yEd. This is now corrected.
The GML parser no longer mixes up Inf and NaN and -Inf now works.
The GML parser now supports nodes with no id field.
The GML parser now performs more stringent checks on the input file, such as verifying that id, source, target and directed fields are not duplicated.
The core data structures (vector, etc.) have overflow checks now.
Deterministic graph generators, as well as most random ones, have overflow checks now.
Graphs no longer lose all their attributes after calling igraph_contract_vertices().
igraph_hrg_init() does not throw an assertion error anymore for zero vertices.
igraph_matrix_complex_create() and igraph_matrix_complex_create_polar() now set their sizes correctly.
igraph_random_walk() took one fewer steps than specified.
igraph_sparsemat_getelements_sorted() did not sort the elements for triplet matrices correctly; this is fixed now.
igraph_write_graph_gml() no longer produces corrupt output when some string attribute values contain " characters.

igraph_clusters() has been renamed to igraph_connected_components(); the old name is deprecated and will be removed in 0.11.
igraph_complex_eq_tol() is now deprecated in favour of igraph_complex_almost_equals().
igraph_get_sparsemat() is deprecated in favour of igraph_get_adjacency_sparse(), and will be removed in 0.11. Note that igraph_get_adjacency_sparse() takes an initialized sparse matrix as input, unlike igraph_get_sparsemat() which takes an uninitialized one.
igraph_get_stochastic_sparsemat() is deprecated in favour of igraph_get_stochastic_sparse(), and will be removed in 0.11. Note that igraph_get_stochastic_sparse() takes an initialized sparse matrix as input, unlike igraph_get_stochastic_sparsemat(), which takes an uninitialized one.
igraph_isomorphic_34() has been deprecated in favour of igraph_isomorphic(). Note that igraph_isomorphic() calls an optimized version for directed graphs of size 3 and 4, and undirected graphs with 3-6 vertices, so there is no need for a separate function.
igraph_laplacian() is now deprecated; use igraph_get_laplacian() or igraph_get_laplacian_sparse() depending on whether you need a dense or a sparse matrix.
igraph_lattice() has been renamed to igraph_square_lattice() to indicate that this function generates square lattices only. The old name is deprecated and will either be removed in 0.11 or will be changed to become a generic lattice generator that also supports other types of lattices.
igraph_local_scan_neighborhood_ecount() is now deprecated in favour of igraph_local_scan_subset_ecount().
igraph_matrix_all_e_tol() is now deprecated in favour of igraph_matrix_all_almost_e().
igraph_matrix_copy() is now deprecated; use igraph_matrix_init_copy() instead. The new name emphasizes that the function initializes the first argument instead of expecting an already-initialized target matrix. The old name will be removed in 0.11.
igraph_matrix_e() and igraph_matrix_e_ptr() have been renamed to igraph_matrix_get() and igraph_matrix_get_ptr(). The old names are deprecated and will be removed in 0.11.
igraph_random_edge_walk() has been deprecated by igraph_random_walk() to support edges and/or vertices for the random walk in a single function. It will be removed in 0.11.
igraph_read_graph_dimacs() has been renamed to igraph_read_graph_dimacs_flow(); the old name is deprecated and might be re-used as a generic DIMACS reader in the future. Also, the function now uses igraph_integer_t as the source and target vertex IDs instead of a long int.
igraph_shortest_paths() and related functions were renamed to igraph_distances(); the old name was unfortunate because these functions calculated path lengths only and not the paths themselves. The old names are deprecated and will be removed in 0.11.
igraph_sparsemat_copy(), igraph_sparsemat_diag() and igraph_sparsemat_eye() have been renamed to igraph_sparsemat_init_copy(), igraph_sparsemat_init_diag() and igraph_sparsemat_init_eye() to indicate that they initialize a new sparse matrix. The old names are deprecated and will be removed in 0.11.
igraph_strvector_add() has been renamed to igraph_strvector_push_back() for sake of consistency with other vector-like data structures; the old name is deprecated and will be removed in 0.11.
igraph_strvector_copy() has been renamed to igraph_strvector_init_copy() for sake of consistency with other vector-like data structures; the old name is deprecated and will be removed in 0.11.
igraph_strvector_get() now returns a const char* and not a char* to indicate that you are not supposed to modify the string in the vector directly. If you do want to modify it and you are aware of the implications (i.e. the new string must not be longer than the original one), you can cast away the constness of the return value before modifying it.
igraph_strvector_set2() has been renamed to igraph_strvector_set_len(); the old name is deprecated and will be removed in 0.11.
igraph_tree() has been renamed to igraph_kary_tree(); the old name is deprecated and will be removed in 0.11.
igraph_vector_e() and igraph_vector_e_ptr() have been renamed to igraph_vector_get() and igraph_vector_get_ptr(). The old names are deprecated and will be removed in 0.11.
igraph_vector_e_tol() is now deprecated in favour of igraph_vector_all_almost_e().
igraph_vector_copy() is now deprecated; use igraph_vector_init_copy() instead. The new name emphasizes that the function initializes the first argument instead of expecting an already-initialized target vector. The old name will be removed in 0.11.
igraph_vector_init_seq() is now deprecated in favour of igraph_vector_init_range(), which uses C-style intervals (closed from the left and open from the right).
igraph_vs_seq(), igraph_vss_seq(), igraph_es_seq() and igraph_ess_seq() are now deprecated in favour of igraph_vs_range(), igraph_vss_range(), igraph_es_range() and igraph_ess_range() because these use C-style intervals (closed from the left, open from the right).
igraph_write_graph_dimacs() has been renamed to igraph_write_graph_dimacs_flow(); the old name is deprecated and might be re-used as a generic DIMACS writer in the future. Also, the function now uses igraph_integer_t as the source and target vertex IDs instead of a long int.
igraph_zeroin() is deprecated and will be removed in 0.11, with no replacement. The function is not graph-related and was never part of the public API.
The macros igraph_Calloc, igraph_Realloc and igraph_Free have been deprecated in favour of IGRAPH_CALLOC, IGRAPH_REALLOC and IGRAPH_FREE to simplify the API. The deprecated variants will be removed in 0.11.

Documentation improvements.
Support for Intel's LLVM-based compiler.

igraph_reverse_edges() reverses the specified edges in the graph while preserving all attributes.

The IGRAPH_ARPACK_PROD error code is no longer used. Instead, the specific error encountered while doing matrix multiplication is reported.
XML external entities are not resolved any more when parsing GraphML files to prevent XML external entity injection (XXE) attacks. Standard XML entities like < or " still work.

Fixed incorrect results from igraph_local_scan_1_ecount() when the graph was directed but the mode was IGRAPH_ALL and some nodes had loop edges. See issue #2092.
Fixed incorrect counting of self-loops in igraph_local_scan_neighborhood_ecount() when the graph was undirected.
In some rare edge cases, igraph_pagerank() with the ARPACK method and igraph_hub_score() / igraph_authority_score() could return incorrect results. The problem could be detected by checking that the returned eigenvalue is not negative. See issue #2090.
igraph_permute_vertices() now checks for out-of-range indices and duplicates in the permutation vector.
igraph_create() now checks for non-finite vertex indices in the edges vector.
igraph_eigenvector_centrality() would return incorrect scores when some weights were negative.
igraph_es_seq() and igraph_ess_seq() did not include the to vertex in the sequence.
igraph_eit_create() and igraph_vit_create() now check that all edge/vertex indices are in range when creating iterators from sequence-type selectors.
igraph_grg_game() now validates its arguments.
igraph_layout_drl() and its 3D version now validate their inputs.
igraph_layout_kamada_kawai(), igraph_layout_fruchterman_reingold(), igraph_layout_drl(), as well as their 3D versions now check for non-positive weights.
igraph_asymmetric_preference_game() interpreted its type_dist_matrix argument incorrectly.
Fixed incorrect result of igraph_community_spinglass() for null and singleton graphs.
igraph_layout_gem() does not crash any more for graphs with only a single vertex.
igraph_bridges() no longer uses recursion and thus is no longer prone to stack overflow.
Include paths of dependent packages would be specified incorrectly in some environments.

Documentation improvements.

igraph_community_walktrap() now uses double precision floating point operations internally instead of single precision.
In igraph_community_leiden(), the nb_clusters output parameter is now optional (i.e. it can be NULL).
igraph_read_graph_graphml() no longer attempts to temporarily set the C locale, and will therefore not work correctly if the current locale uses a decimal comma.

igraph_community_walktrap() would return an invalid modularity vector when the merges matrix was not requested.
igraph_community_walktrap() would return a modularity vector that was too long for disconnected graphs. This would cause a failure in some weighted graphs when the membership vector was requested.
igraph_community_walktrap() now checks the weight vector: only non-negative weights are accepted, and all vertices must have non-zero strength.
igraph_community_walktrap() now returns a modularity score of NaN for graphs with no edges.
igraph_community_fast_greedy() now returns a modularity score of NaN for graphs with no edges.
igraph_community_edge_betweenness() now returns a modularity vector with a single NaN entry for graph with no edges. Previously it returned a zero-length vector.
igraph_community_leading_eigenvector() does not ignore non-ARPACK-related errors from igraph_arpack_rssolve() any more.
igraph_preference_game() now works correctly when fixed_size is true and type_dist is not given; earlier versions had a bug where more than half of the vertices mistakenly ended up in group 0.
Fixed a memory leak in igraph_hrg_fit() when using start=1.
igraph_write_graph_dot() now outputs NaN values unchanged.
igraph_write_graph_dot() no longer produces invalid DOT files when empty string attributes are present.
igraph_layout_fruchterman_reingold() and igraph_layout_kamada_kawai(), as well as their 3D versions, did not respect vertex coordinate bounds (xmin, xmax, etc.) when minimum values were large or maximum values were small. This is now fixed.
The initial coordinates of the Kamada-Kawai layout (igraph_layout_kamada_kawai() and igraph_layout_kamada_kawai_3d()) are chosen to be more in line with the original publication, improving the stability of the result. See isse #963. This changes the output of the function for the same graph, compared with previous versions. To obtain the same layout, initialize coordinates with igraph_layout_circle() (in 2D) or igraph_layout_sphere() (in 3D).
Improved numerical stability in Kamada-Kawai layout.
Corrected a problem in the calculation of displacements in igraph_layout_fruchterman_reingold() and its 3D version. This fixes using the "grid" variant of the algorithm on disconnected graphs.
igraph_sumtree_search() would consider search intervals open on the left and closed on the right, contrary to the documentation. This is now corrected to closed on the left and open on the right. In some cases this lead to a zero-weight element being returned for a zero search value. See issue #2080.

Greatly improved error reporting from foregin format parsers.
Documentation improvements.

Assertion failure in igraph_bfs() when an empty roots or restricted vector was provided.
igraph_diversity() now returns 0 for degree-1 vertices. Previously it incorrectly returned NaN or +-Inf depending on roundoff errors.
igraph_community_walktrap() does not crash any more when provided with modularity=NULL and membership=NULL.

Documentation improvements.

igraph_get_all_shortest_paths_dijsktra() now uses tolerances when comparing path lengths, and is thus robust to numerical roundoff errors.
igraph_vector_*_swap and igraph_matrix_swap now take O(1) instead of O(n) and accept all sizes.

NCOL and LGL format writers no longer accept "name" and "weight" attributes of invalid types.
The LGL writer could not access numerical weight attributes, potentially leading to crashes.
External PLFIT libraries and their headers are now detected at their standard installation location.
igraph_vector_init() no longer accepts negative vector sizes.
igraph_assortativity_nominal() crashed on the null graph.
Label propagation now ensures that all labels are dominant.
Fixed incorrect partition results for walktrap algorithm (issue #1927)
Negative values returned by igraph_rng_get_integer() and RNG_INTEGER() were incorrect, one larger than they should have been.
igraph_community_walktrap() now checks its steps input argument.
The first modularity value reported by igraph_community_walktrap() was incorrect (it was always zero). This is now fixed.
igraph_correlated_game() would return incorrect results, or exhaust the memory, for most input graphs that were not generated with igraph_erdos_renyi_game_gnp().
igraph_community_label_propagation incorrectly did not result in all labels being dominant (issue #1963, fixed in PR #1966).

The C attribute handler now verifies attribute types when retrieving attributes.
Documentation improvements.

Isomorphism class functions (igraph_isoclass(), igraph_isoclass_subgraph(), igraph_isoclass_create) and motif finder functions (igraph_motifs_randesu(), igraph_motifs_randesu_estimate(), igraph_motifs_randesu_callback()) now support undirected (sub)graphs of sizes 5 and 6. Previsouly only sizes 3 and 4 were supported.

igraph would not build with MinGW when using the vendored GLPK and enabling TLS.
Removed some uses of abort() from vendored libraries, which could unexpectedly shut down the host language of igraph's high-level interfaces.
igraph_community_label_propagation() no longer leaves any vertices unlabeled when they were not reachable from any labeled ones, i.e. the returned membership vector is guaranteed not to contain negative values (#1853).
The Kamada-Kawai layout is now interruptible.
The Fruchterman-Reingold layout is now interruptible.
Fixed a bug in igraph_cmp_epsilon() that resulted in incorrect results for edge betweenness calculations in certain rare cases with x87 floating point math when LTO was also enabled (#1894).
Weighted clique related functions now fall back to the unweighted variants when a null vertex weight vector is given to them.
igraph_erdos_renyi_game_(gnm|gnp) would not produce self-loops for the singleton graph.
Fixed a bug in igraph_local_efficiency() that sometimes erroneously reported zero as the local efficiency of a vertex in directed graphs.
igraph_vector_update() (and its type-specific variants) did not check for memory allocation failure.
Fixed a potential crash in the GraphML reader that would be triggered by some invalid GraphML files.

igraph_is_tree() has improved performance and memory usage.
igraph_is_connected() has improved performance when checking weak connectedness.
Improved error handling in igraph_maximal_cliques() and related functions.
The build system now checks that GLPK is of a compatible version (4.57 or later).
The vendored plfit package was updated to 0.9.3.
You can now build igraph with an external plfit instead of the vendored one.
Documentation improvements.

igraph_reindex_membership() does not allow negative membership indices any more.
igraph_rewire_directed_edges() now generates multigraphs when edge directions are ignored, to make it consistent with the directed case.
Fixed a bug in igraph_gomory_hu_tree() that returned only the equivalent flow tree instead of the cut tree (#1810).
Fixed a bug in the IGRAPH_TO_UNDIRECTED_COLLAPSE mode of igraph_to_undirected() that provided an incorrect merge vector to the attribute handler, leading to problems when edge attributes were merged using an attribute combination (#1814).
Fixed the behaviour of the IGRAPH_ENABLE_LTO option when it was set to AUTO; earlier versions had a bug where AUTO simply checked whether LTO is supported but then did not use LTO even if it was supported.
When using igraph from a CMake project, it is now checked that the project has the C++ language enabled. This is necessary for linking to igraph with CMake.

Improved the root selection method for disconnected graphs in the Reingold-Tilford layout (#1836). The new root selection method provides niceer results if the graph is not a tree, although it is still recommended to use the Sugiyama layout instead, unless the input graph is almost a tree, in which case Reingold-Tilfold may still be preferred.
igraph_decompose() is now much faster for large graphs containing many isolates or small components (#960).
igraph_largest_cliques() and igraph_clique_number() were re-written to use igraph_maximal_cliques_callback() so they are much faster now (#804).
The vendored GLPK has been upgraded to GLPK 5.0.
Documentation improvements.

Unweighted transitivity (i.e. clustering coefficient) calculations now ignore multi-edges and edge directions instead of rejecting multigraphs and directed graphs.
igraph_transitivity_barrat() now returns an error code if the input graph has multiple edges (which is not handled correctly by the implementation yet).

igraph_local_scan_k_ecount() now handles loops correctly.
igraph_transitivity_avglocal_undirected() is no longer slower than igraph_transitivity_local_undirected().
Worked around an invalid warning issued by Clang 9.0 when compiling with OpenMP.

Documentation improvements.

OpenMP is now enabled and used by certain functions (notably PageRank calculation) when the compiler supports it. Set IGRAPH_OPENMP_SUPPORT=OFF at configuration time to disable this.

igraph_get_incidence() no longer reads and writes out of bounds when given a non-bipartite graph, but gives a warning and ignores edges within a part.
igraph_dyad_census() no longer reports an overflow on singleton graphs, and handles loops and multigraphs correctly. Undirected graphs are handled consistently and will no longer give a warning.
igraph_vector_lex_cmp() and igraph_vector_colex_cmp() dereferenced their arguments only once instead of twice, and therefore did not work with igraph_vector_ptr_sort().
igraph_maximal_cliques_subset() and igraph_transitivity_barrat() corrupted the error handling stack ("finally stack") under some circumstances.
CMake package files did not respect CMAKE_INSTALL_LIBDIR. This only affected Linux distributions which install into lib64 or other locations instead of lib.
The parser sources could not be generated when igraph was in a location that contained spaces in its path.
igraph no longer links to the math library (libm) when this is not necessary.
_CRT_SECURE_NO_WARNINGS is now defined during compilation to enable compatibility with UWP.
Fixed a compilation issue on MSYS / MinGW when link-time optimization was enabled and the MSYS Makefiles CMake generator was used. Some source files in igraph were renamed as a consequence, but these should not affect users of the library.

igraph_rng_min() is now deprecated; assume a constant zero as its return value if you used this function in your own code.

Updated the vendored CXSparse library to version 3.2.0

CMake package files are now installed with igraph. This allows find_package(igraph) to find igraph and detect the appropriate compilation options for projects that link to it.

igraph can now be used as a CMake subproject in other CMake-based projects.
The documentaton can now be built from the release tarball.
Configuration will no longer fail when the release tarball is extracted into a subdirectory of an unrelated git repository.
The generated pkg-config file was incorrect when CMAKE_INSTALL_<dir> variables were absolute paths.
On Unix-like systems, the library name is now libigraph.so.0.0.0, as it used to be for igraph 0.8 and earlier.
Fixed a return type mismatch in parser sources, and fixed some warnings with recent versions of gcc.
Fixed a bug in igraph_get_shortest_paths_dijkstra() and igraph_get_shortest_paths_bellman_ford() that returned incorrect results for unreachable vertices.

Improved installation instructions and tutorial.

igraph_vector_lex_cmp() and igraph_vector_colex_cmp() for lexicographic and colexicographic comparison of vectors. These functions may also be used for sorting.

igraph_community_multilevel() is now randomized (PR #1696, thanks to Daniel Noom).

CMake settings that controlled the library installation directory name, such as CMAKE_INSTALL_LIBDIR, were not respected.
Under some conditions, the generated pkg-config file contained an incorrect include directory path.
The following functions were not exported from the shared library: igraph_subcomponent(), igraph_stack_ptr_free_all(), igraph_stack_ptr_destroy_all(), igraph_status_handler_stderr(), igraph_progress_handler_stderr().
Built-in random number generators (igraph_rngtype_mt19937, igraph_rngtype_rand, igraph_rngtype_glibc2) were not exported from the shared library.
igraph_layout_graphopt() no longer rounds the spring_length parameter to an integer.
igraph_get_all_shortest_paths_dijkstra() no longer modifies the res vector's item destructor.
igraph_get_shortest_path_bellman_ford() did not work correctly when calculating paths to all vertices.
igraph_arpack_rnsolve() checks its parameters more carefully.
igraph_community_to_membership() does not crash anymore when csize is requested but membership is not.
igraph_citing_cited_type_game(): fixed memory leaks (PR #1700, thanks to Daniel Noom).
igraph_transitivity_undirected(), igraph_transitivity_avglocal_undirected() and igraph_transitivity_barrat() no longer trigger an assertion failure when used with the null graph (PRs #1709, #1710).
igraph_(personalized_)pagerank() would return incorrect results for weighted multigraphs with fewer than 128 vertices when using IGRAPH_PAGERANK_ALGO_PRPACK.
igraph_diversity() now checks its input more carefully, and throws an error when the input graph has multi-edges or is directed.
igraph_shortest_paths_johnson() would return incorrect results when the to argument differed from from (thanks to Daniel Noom).
igraph_is_graphical() would fail to set the result variable for certain special degree sequences in the undirected simple graph case.
Non-maximal clique finding functions would sometimes return incomplete results when finding more than 2147483647 (i.e. 2^31 - 1) cliques.
GLPK internal errors no longer crash igraph.
Fixed some potential memory leaks that could happen on error conditions or when certain functions were interrupted.
When testing a DLL build on Windows, the PATH was sometimes not set correctly, causing the tests to fail (PR #1692).
When compiling from the git repository (as opposed to the release tarball), the build would fail with recent versions of bison and flex.

Documentation improvements.
Much faster documentation builds.
Allow using a pre-generated arith.h header for f2c when cross-compiling; see the Installation section of the documentation.
The IGRAPH_ENABLE_LTO build option now supports the AUTO value, which uses LTO only if the compiler supports it. Warning: CMake may not always be able to detect that LTO is not fully supported. Therefore, the default setting is OFF.
The following functions are now interruptible: igraph_grg_game(), igraph_sbm_game(), igraph_barabasi_game(), igraph_barabasi_aging_game().
Functions that use GLPK, such as igraph_feedback_arc_set() and igraph_community_optimal_modularity() are now interruptible.
Add support for older versions of Clang that do not recognize the -Wno-varargs flag.

Big thanks to Daniel Noom for continuing to expand the test suite and discovering and fixing several bugs in the process!

Eulerian paths/cycles (PR #1346):
igraph_is_eulerian() finds out whether an Eulerian path/cycle exists.
igraph_eulerian_path() returns an Eulerian path.
igraph_eulerian_cycle() returns an Eulerian cycle.
Efficiency (PR #1344):
igraph_global_efficiency() computes the global efficiency of a network.
igraph_local_efficiency() computes the local efficiency around each vertex.
igraph_average_local_efficiency() computes the mean local efficiency.
Degree sequences (PR #1445):
igraph_is_graphical() checks if a degree sequence has a realization as a simple or multigraph, with or without self-loops.
igraph_is_bigraphical() checks if two degree sequences have a realization as a bipartite graph.
igraph_realize_degree_sequence() now supports constructing non-simple graphs as well.
There is a new fatal error handling mechanism (PR #1548):
igraph_set_fatal_handler() sets the fatal error handler. It is the only function in this functionality group that is relevant to end users.
The macro IGRAPH_FATAL() and the functions igraph_fatal() and igraph_fatalf() raise a fatal error. These are for internal use.
IGRAPH_ASSERT() is a replacement for the assert() macro. It is for internal use.
igraph_fatal_handler_abort() is the default fatal error handler.
The new IGRAPH_WARNINGF, IGRAPH_ERRORF and IGRAPH_FATALF macros provide warning/error reporting with printf-like syntax. (PR #1627, thanks to Daniel Noom!)
igraph_average_path_length_dijkstra() computes the mean shortest path length in weighted graphs (PR #1344).
igraph_get_shortest_paths_bellman_ford() computes the shortest paths (including the vertex and edge IDs along the paths) using the Bellman-Ford algorithm (PR #1642, thanks to Guy Rozenberg). This makes it possible to calculate the shortest paths on graphs with negative edge weights, which was not possible before with Dijkstra's algorithm.
igraph_get_shortest_path_bellman_ford() is a wrapper for igraph_get_shortest_paths_bellman_ford() for the single path case.
igraph_is_same_graph() cheks that two labelled graphs are the same (PR #1604).
Harmonic centrality (PR #1583):
igraph_harmonic_centrality() computes the harmonic centrality of vertices.
igraph_harmonic_centrality_cutoff() computes the range-limited harmonic centrality.
Range-limited centralities, currently equivalent to the old functions with names ending in _estimate (PR #1583):
igraph_closeness_cutoff().
igraph_betweenness_cutoff().
igraph_edge_betweenness_cutoff().
igraph_vector_is_any_nan() checks if any elements of an igraph_vector_t is NaN.
igraph_inclist_size() returns the number of vertices in an incidence list.
igraph_lazy_adjlist_size() returns the number of vertices in a lazy adjacency list.
igraph_lazy_inclist_size() returns the number of vertices in a lazy incidence list.
igraph_bfs_simple() now provides a simpler interface to the breadth-first search functionality.

igraph now uses a CMake-based build sysyem.
GMP support can no longer be disabled. When GMP is not present on the system, igraph will use an embedded copy of Mini-GMP (PR #1549).
Bliss has been updated to version 0.75. Bliss functions are now interruptible. Thanks to Tommi Junttila for making this possible!
Adjacency and incidence lists:
igraph_adjlist_init() and igraph_lazy_adjlist_init() now require the caller to specify what to do with loop and multiple edges.
igraph_inclist_init() and igraph_lazy_inclist_init() now require the caller to specify what to do with loop edges.
Adjacency and incidence lists now use igraph_vector_int_t consistently.
Community detection:
igraph_community_multilevel(): added resolution parameter.
igraph_community_fluid_communities(): graphs with no vertices or with one vertex only are now supported; they return a trivial partition.
Modularity:
igraph_modularity() and igraph_modularity_matrix(): added resolution parameter.
igraph_modularity() and igraph_modularity_matrix() now support the directed version of modularity.
igraph_modularity() returns NaN for graphs with no edges to indicate that the modularity is not well-defined for such graphs.
Centralities:
cutoff=0 is no longer interpreted as infinity (i.e. no cutoff) in betweenness, edge_betweenness and closeness. If no cutoff is desired, use a negative value such as cutoff=-1.
The nobigint argument has been removed from igraph_betweenness(), igraph_betweenness_estimate() and igraph_centralization_betweenness(), as it is not longer needed. The current implementation is more accurate than the old one using big integers.
igraph_closeness() now considers only reachable vertices during the calculation (i.e. the closeness is calculated per-component in the undirected case) (PR #1630).
igraph_closeness() gained two additional output parameters, reachable_count and all_reachable, returning the number of reached vertices from each vertex, as well as whether all vertices were reachable. This allows for computing various generalizations of closeness for disconnected graphs (PR #1630).
igraph_pagerank(), igraph_personalized_pagerank() and igraph_personalized_pagerank_vs() no longer support the IGRAPH_PAGERANK_ALGO_POWER method. Their options argument now has type igraph_arpack_options_t * instead of void *.
Shortest paths (PR #1344):
igraph_average_path_length() now returns the number of disconnected vertex pairs in the new unconn_pairs output argument.
igraph_diameter() now return the result as an igraph_real_t instead of an igraph_integer_t.
igraph_average_path_length() and igraph_diameter() now return IGRAPH_INFINITY when unconn=FALSE and the graph is not connected. Previously they returned the number of vertices.
Trait-based random graph generators:
igraph_callaway_traits_game() and igraph_establishment_game() now have an optional output argument to retrieve the generated vertex types.
igraph_callaway_traits_game() and igraph_establishment_game() now allow omitting the type distribution vector, in which case they assume a uniform distribution.
igraph_asymmetric_preference_game() now accept a different number of in-types and out-types.
igraph_subisomorphic_lad() now supports graphs with self-loops.
igraph_is_chordal() and igraph_maximum_cardinality_search() now support non-simple graphs and directed graphs.
igraph_realize_degree_sequence() has an additional argument controlling whether multi-edges or self-loops are allowed.
igraph_is_connected() now returns false for the null graph; see https://github.com/igraph/igraph/issues/1538 for the reasoning behind this decision.
igraph_lapack_ddot() is renamed to igraph_blas_ddot().
igraph_to_directed(): added RANDOM and ACYCLIC modes (PR #1511).
igraph_topological_sorting() now issues an error if the input graph is not acyclic. Previously it issued a warning.
igraph_vector_(which_)(min|max|minmax)() now handles NaN elements.
igraph_i_set_attribute_table() is renamed to igraph_set_attribute_table().
igraph_i_sparsemat_view() is renamed to igraph_sparsemat_view().

igraph_is_degree_sequence() and igraph_is_graphical_degree_sequence() are deprecated in favour of the newly added igraph_is_graphical().
igraph_closeness_estimate() is deprecated in favour of the newly added igraph_closeness_cutoff().
igraph_betweenness_estimate() and igraph_edge_betweenness_estimate() are deprecated in favour of the newly added igraph_betweenness_cutoff() and igraph_edge_betweenness_cutoff().
igraph_adjlist_remove_duplicate() and igraph_inclist_remove_duplicate() are now deprecated in favour of the new constructor arguments in igraph_adjlist_init() and igraph_inclist_init().

The following functions, all deprecated in igraph 0.6, have been removed (PR #1562):
igraph_adjedgelist_init(), igraph_adjedgelist_destroy(), igraph_adjedgelist_get(), igraph_adjedgelist_print(), igraph_adjedgelist_remove_duplicate().
igraph_lazy_adjedgelist_init(), igraph_lazy_adjedgelist_destroy(), igraph_lazy_adjedgelist_get(), igraph_lazy_adjedgelist_get_real().
igraph_adjacent().
igraph_es_adj().
igraph_subgraph().
igraph_pagerank_old(), deprecated in 0.7, has been removed.
igraph_vector_bool and igraph_matrix_bool functions that relied on inequality-comparing igraph_bool_t values are removed.

Betweenness calculations are no longer at risk from integer overflow.
The actual cutoff distance used in closeness calculation was one smaller than the cutoff parameter. This is corrected (PR #1630).
igraph_layout_gem() was not interruptible; now it is.
igraph_barabasi_aging_game() now checks its parameters more carefully.
igraph_callaway_traits_game() and igraph_establishment_game() now check their parameters.
igraph_lastcit_game() checks its parameters more carefully, and no longer crashes with zero vertices (PR #1625).
igraph_cited_type_game() incorrectly rounded the attractivity vector entries to integers.
igraph_residual_graph() now returns the correct residual capacities; previously it wrongly returned the original capacities (PR #1598).
igraph_psumtree_update() now checks for negative values and NaN.
igraph_communities_spinglass(): fixed several memory leaks in the IGRAPH_SPINCOMM_IMP_NEG implementation.
igraph_incident() now returns edges in the same order as igraph_neighbors().
igraph_modularity_matrix() returned incorrect results for weighted graphs. This is now fixed. (PR #1649, thanks to Daniel Noom!)
igraph_lapack_dgetrf() would crash when passing NULL for its ipiv argument (thanks for the fix to Daniel Noom).
Some igraph_matrix functions would fail to report errors on out-of-memory conditions.
igraph_maxdegree() now returns 0 for the null graph or empty vector set. Previously, it did not handle this case.
igraph_vector_bool_all_e() now considers all nonzero (i.e. "true") values to be the same.
PageRank (PR #1640):
igraph_(personalized_)pagerank(_vs)() now check their parameters more carefully.
igraph_personalized_pagerank() no longer modifies its reset parameter.
igraph_(personalized_)pagerank(_vs): the IGRAPH_PAGERANK_ALGO_ARPACK method now handles self-loops correctly.
igraph_personalized_pagerank(_vs)(): the result retuned for edgeless or all-zero-weight graphs with the IGRAPH_PAGERANK_ALGO_ARPACK ignored the personalization vector. This is now corrected.
igraph_personalized_pagerank(_vs)() with a non-uniform personalization vector, a disconnected graph and the IGRAPH_PAGERANK_ALGO_PRPACK method would return results that were inconsistent with IGRAPH_PAGERANK_ALGO_ARPACK. This happened because PRPACK always used a uniform reset distribution when the random walk got stuck in a sink vertex. Now it uses the user-specified reset distribution for this case as well.
Fixed crashes in several functions when passing a weighted graph with zero edges (due to vector_min being called on the zero-length weight vector).
Fixed problems in several functions when passing in a graph with zero vertices.
Weighted betweenness, closeness, PageRank, shortest path calculations and random walk functions now check if any weights are NaN.
Many functions now reject input arguments containing NaN values.
Compatibility with the PGI compiler.

Documentation improvements.
Improved error and warning messages.
More robust error handling.
General code cleanup to reduce the number of compiler warnings.
igraph's source files have been re-organized for better maintainability.
Debugging aid: When igraph is build with AddressSanitizer, the default error handler prints a stack trace before exiting.
igraph can now be built with an external CXSparse library.
The references to igraph source files in error and warning messages are now always relative to igraph's base directory.
When igraph is built as a shared library, only public symbols are exported even on Linux and macOS.

Thanks to Daniel Noom for significantly expanding igraph's test coverage and exposing several issues in the process!

igraph_write_graph_pajek(): the function now always uses the platform-native line endings (CRLF on Windows, LF on Unix and macOS). Earlier versions tried to enforce Windows line endings, but this was error-prone, and since all recent versions of Pajek support both line endings, enforcing Windows line endings is not necessary any more.

Fixed several compilation issues with MINGW32/64 (PR #1554)
igraph_layout_davidson_harel() was not interruptible; now it is.
Added a missing memory cleanup call in igraph_i_cattribute_combine_vertices().
Fixed a few memory leaks in test cases.

igraph_i_cattribute_combine_vertices(): fixed invalid cleanup code that eventually filled up the "finally" stack when combining vertices with attributes extensively.
igraph_hrg_sample(): fixed incorrect function prototype
igraph_is_posinf() and igraph_is_neginf(): fixed incorrect result on platforms where the sign of the result of isinf() is not indicative of the sign of the input.
Fixed building with vendored LAPACK and external BLAS
Fixed building with XCode 12.2 on macOS

Documentation improvements
General code cleanup to reduce the number of compiler warnings

igraph_vector_binsearch_slice() performs binary search on a sorted slice of a vector.

igraph_eigenvector_centrality() assumes the adjacency matrix of undirected graphs to have twice the number of self-loops for each vertex on the diagonal. This makes the results consistent between an undirected graph and its directed equivalent when each edge is replaced by a mutual edge pair.

igraph_isomorphic() now verifies that the input graphs have no multi-edges (PR #1464).
igraph_difference() was creating superfluous self loops (#597).
igraph_count_multiple() was giving incorrect results for self-loops in directed graph (PR #1399).
igraph_betweenness_estimate(): fixed incorrect results with finite cutoff (PR #1392).
igraph_count_multiple() was giving incorrect results for self-loops in directed graph (PR #1399).
igraph_eigen_matrix_symmetric(): fixed incorrect matrix multiplication (PR #1379).
Corrected several issues that could arise during an error condition (PRs #1405, #1406, #1438).
igraph_realize_degree_sequence() did not correctly detect some non-graphical inputs.
igraph_is_graphical_degree_sequence(): fixed incorrect results in undirected case (PR #1441).
igraph_community_leiden(): fixed incorrect result when self-loops are present (PR #1476).
igraph_eigenvector_centrality(): fixed incorrect value for isolated vertices in weighted graphs.
igraph_eigenvector_centrality(): corrected the handling of self-loops.
igraph_layout_reingold_tilford(): fixed an issue where branches of the tree would sometimes overlap.

igraph_degree_sequence_game(): improved performance with IGRAPH_DEGSEQ_SIMPLE_NO_MULTIPLE_UNIFORM method.
Improved the robustness of the test suite.
Documentation improvements.
Improved error and warning messages.
Improved compatibility with recent versions of Microsoft Visual C.

Improved argument checking: igraph_all_st_mincuts() and igraph_sir()
Improved interruptibility: igraph_sir()

igraph_community_leiden(): fixed crash when interrupting
The tests are now more robust. Some incorrect test failures were fixed when running on i386 architecture, or when using different versions of external dependencies.

Improved error messages from igraph_sir().
Improved compatibility with more recent versions of Microsoft Visual C.

Improved interruptability: igraph_degree_sequence_game()
Improved argument checking: igraph_forest_fire_game()
Updated the plfit library to version 0.8.1

igraph_community_edge_betweenness(): fix for graphs with no edges (PR #1312)
igraph_bridges() now handles multigraphs correctly (PR #1335)
igraph_avg_nearest_neighbor_degree(): fix for memory leak in weighted case (PR #1339)
igraph_community_leiden(): fix crash bug (PR #1357)

Included ACKOWLEDGEMENTS.md
Documentation improvements

Trees
igraph_to_prufer() and igraph_from_prufer() convert labelled trees to/from Prüfer sequences
igraph_tree_game() samples uniformly from the set of labelled trees
igraph_is_tree() checks if a graph is a tree
igraph_random_spanning_tree() picks a spanning tree of a graph uniformly at random
igraph_random_edge_walk() returns the indices of edges traversed by a random walk; useful for multigraphs
Community detection
igraph_community_fluid_communities() detects communities based on interacting fluids
igraph_community_leiden() detects communities with the Leiden method
Cliques
igraph_maximal_cliques_hist() counts maximal cliques of each size
igraph_maximal_cliques_callback() calls a function for each maximal clique
igraph_clique_size_hist() counts cliques of each size
igraph_cliques_callback() calls a function for each clique
igraph_weighted_cliques() finds weighted cliques in graphs with integer vertex weights
igraph_weighted_clique_number() computes the weighted clique number
igraph_largest_weighted_cliques() finds the largest weighted cliques
Graph generators
igraph_hsbm_game() for a hierarchical stochastic block model
igraph_hsbm_list_game() for a more general hierarchical stochastic block model
igraph_correlated_game() generates pairs of correlated random graphs by perturbing existing adjacency matrix
igraph_correlated_pair_game() generates pairs of correlated random graphs
igraph_tree_game() samples uniformly from the set of labelled trees
igraph_dot_product_game() generates a random dot product graph
igraph_realize_degree_sequence() creates a single graph with a given degree sequence (Havel-Hakimi algorithm)
Graph embeddings
igraph_adjacency_spectral_embedding() and igraph_laplacian_spectral_embedding() provide graph embedddings
igraph_dim_select() provides dimensionality selection for singular values using profile likelihood
Isomorphism
igraph_automorphism_group() computes the generators of the automorphism group of a simple graph
igraph_simplify_and_colorize() encodes edge and self-loop multiplicities into edge and vertex colors; use in conjunction with VF2 to test isomorphism of non-simple graphs
Other
igraph_bridges() finds edges whose removal would disconnect a graph
igraph_vertex_coloring_greedy() computes a vertex coloring using a greedy algorithm
igraph_rewire_directed_edges() randomly rewires only the starting points or only the endpoints of directed edges
Various igraph_local_scan_* functions provide local counts and statistics of neighborhoods
igraph_sample_sphere_surface() samples points uniformly from the surface of a sphere
igraph_sample_sphere_volume() samples points uniformly from the volume of a sphere
igraph_sample_dirichlet() samples points from a Dirichlet distribution
igraph_malloc(), to be paired with the existing igraph_free()

igraph_degree_sequence_game(): new method added for uniform sampling: IGRAPH_DEGSEQ_SIMPLE_NO_MULTIPLE_UNIFORM
igraph_modularity_matrix(): removed membership argument (PR #1194)
igraph_avg_nearest_neighbor_degree(): added mode and neighbor_degree_mode arguments (PR #1214).
igraph_get_all_simple_paths(): added cutoff argument (PR #1232).
igraph_unfold_tree(): no longer preserves edge ordering of original graph
igraph_decompose(): support strongly connected components
igraph_isomorphic_bliss(), igraph_canonical_permutation(), igraph_automorphisms(): added additional arguments to support vertex colored graphs (PR #873)
igraph_extended_chordal_ring: added argument to support direction (PR #1096), and fixed issue #1093.

The Bliss isomorphism library was updated to version 0.73. This version adds support for vertex colored and directed graphs.
igraph now uses the high-performance Cliquer library to find (non-maximal) cliques
Provide proper support for Windows, using __declspec(dllexport) and __declspec(dllimport) for DLLs and static usage by using #define IGRAPH_STATIC 1.
Provided integer versions of dqueue and stack data types.

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igraph Network Analysis and Visualization

src/vendor/cigraph/CHANGELOG.md In igraph: Network Analysis and Visualization

igraph C library changelog

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0.10.13

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0.10.12 - 2024-05-06

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0.10.11 - 2024-04-02

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0.10.10 - 2024-02-13

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0.10.9 - 2024-02-02

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0.10.8 - 2023-11-17

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0.10.7 - 2023-09-04

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0.10.6 - 2023-07-13

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0.10.4 - 2023-01-26

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0.10.2 - 2022-10-14

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igraph
Network Analysis and Visualization

src/vendor/cigraph/CHANGELOG.md
In igraph: Network Analysis and Visualization