layout_tree_unrooted: unrooted tree layout

In graphlayouts: Additional Layout Algorithms for Network Visualizations

unrooted tree layout

Description

arranges the nodes of a tree (or forest) in the plane without a designated root, using algorithms developed for drawing phylogenies.

Usage

layout_as_tree_unrooted(
  g,
  mode = c("equalangle", "equaldaylight", "stress"),
  weights = NA,
  daylight_iter = 15,
  iter = 500,
  tol = 1e-04,
  bbox = 30
)

layout_igraph_tree_unrooted(
  g,
  mode = c("equalangle", "equaldaylight", "stress"),
  weights = NA,
  daylight_iter = 15,
  iter = 500,
  tol = 1e-04,
  bbox = 30,
  circular
)

Arguments

g	igraph object. Each connected component must be a tree (acyclic).
mode	which algorithm to use. One of "equalangle" (default), "equaldaylight" or "stress". See details.
weights	possibly a numeric vector with edge weights, interpreted as branch lengths. If this is NULL and the graph has a weight edge attribute, then the attribute is used. If this is NA then unit branch lengths are used (even if the graph has a weight attribute). By default, unit branch lengths are used.
daylight_iter	number of refinement sweeps for mode = "equaldaylight".
iter	number of iterations during stress optimization (only used for mode = "stress").
tol	stopping criterion for stress optimization (only used for mode = "stress").
bbox	width of layout. Only relevant to determine the placement of disconnected components (forests).
circular	not used

Details

Three algorithms are available:

• "equalangle" (Felsenstein, 1989): each subtree is allotted an angular wedge proportional to its number of leaves. Linear time, but can look crowded on unbalanced trees.

• "equaldaylight" (Felsenstein): iteratively equalizes the angular gaps ("daylight") around each internal node, starting from the equal-angle layout, for a more balanced drawing.

• "stress": stress majorization using the patristic (tree path-length) distances as target distances, reusing the package's stress engine.

Branch lengths (edge weights) are respected when present; otherwise unit lengths are used.

The layout_igraph_* function should not be used directly. It is only used as an argument for plotting with 'igraph'. 'ggraph' natively supports the layout.

Value

matrix of xy coordinates

References

Felsenstein, J. (1989). PHYLIP - Phylogeny Inference Package (Version 3.2). Cladistics, 5, 164-166.

Bachmaier, C., Brandes, U., & Schlieper, B. (2005). Drawing phylogenetic trees. In International Symposium on Algorithms and Computation (pp. 1110-1121). Springer, Berlin, Heidelberg.

Examples

library(igraph)
g <- make_tree(20, 3, mode = "undirected")

xy <- layout_as_tree_unrooted(g)
xy <- layout_as_tree_unrooted(g, mode = "equaldaylight")

graphlayouts documentation built on July 22, 2026, 5:11 p.m.