subgraph_isomorphisms: All isomorphic mappings between a graph and subgraphs of...

In igraph: Network Analysis and Visualization

All isomorphic mappings between a graph and subgraphs of another graph

Description

All isomorphic mappings between a graph and subgraphs of another graph

Usage

subgraph_isomorphisms(
  pattern,
  target,
  method = c("lad", "vf2"),
  ...,
  callback = NULL
)

Arguments

pattern	The smaller graph, it might be directed or undirected. Undirected graphs are treated as directed graphs with mutual edges.
target	The bigger graph, it might be directed or undirected. Undirected graphs are treated as directed graphs with mutual edges.
method	The method to use. Possible values: ‘auto’, ‘lad’, ‘vf2’. See their details below.
...	Additional arguments, passed to the various methods.
callback	Optional callback function to call for each subisomorphism found. If provided, the function should accept two arguments: map12 (integer vector mapping vertex IDs from pattern to target, 1-based indexing) and map21 (integer vector mapping vertex IDs from target to pattern, 1-based indexing). The function should return FALSE to continue the search or TRUE to stop it. If NULL (the default), all subisomorphisms are collected and returned as a list. Only supported for method = "vf2". Important limitation: Callback functions must NOT call any igraph functions (including simple queries like vcount() or ecount()). Doing so will cause R to crash due to reentrancy issues. Extract any needed graph information before calling the function with a callback, or use collector mode (the default) and process results afterward.

Value

If callback is NULL, returns a list of vertex sequences, corresponding to all mappings from the pattern graph to the target graph. If callback is provided, returns NULL invisibly.

‘lad’ method

This is the LAD algorithm by Solnon, see the reference below. It has the following extra arguments:

domains

If not NULL, then it specifies matching restrictions. It must be a list of target vertex sets, given as numeric vertex ids or symbolic vertex names. The length of the list must be vcount(pattern) and for each vertex in pattern it gives the allowed matching vertices in target. Defaults to NULL.

induced

Logical scalar, whether to search for an induced subgraph. It is FALSE by default.

time.limit

The processor time limit for the computation, in seconds. It defaults to Inf, which means no limit.

‘vf2’ method

This method uses the VF2 algorithm by Cordella, Foggia et al., see references below. It supports vertex and edge colors and have the following extra arguments:

vertex.color1, vertex.color2

Optional integer vectors giving the colors of the vertices for colored graph isomorphism. If they are not given, but the graph has a “color” vertex attribute, then it will be used. If you want to ignore these attributes, then supply NULL for both of these arguments. See also examples below.

edge.color1, edge.color2

Optional integer vectors giving the colors of the edges for edge-colored (sub)graph isomorphism. If they are not given, but the graph has a “color” edge attribute, then it will be used. If you want to ignore these attributes, then supply NULL for both of these arguments.

Related documentation in the C library

get_subisomorphisms_vf2(), vcount(), edges(), get_eids(), ecount()

See Also

Other graph isomorphism: canonical_permutation(), count_isomorphisms(), count_subgraph_isomorphisms(), graph_from_isomorphism_class(), isomorphic(), isomorphism_class(), isomorphisms(), subgraph_isomorphic()

igraph documentation built on May 4, 2026, 9:07 a.m.