Returns a minimum spanning tree or forest on an undirected graph G.

An undirected graph. If G is connected, then the algorithm finds a spanning tree. Otherwise, a spanning forest is found.

Data key to use for edge weights.

The algorithm to use when finding a minimum spanning tree. Valid choices are ‘kruskal’, ‘prim’, or ‘boruvka’. The default is ‘kruskal’.

If a NaN is found as an edge weight normally an exception is raised. If ignore_nan is True then that edge is ignored instead.

A minimum spanning tree or forest.

Notes

For Borůvka’s algorithm, each edge must have a weight attribute, and each edge weight must be distinct.

For the other algorithms, if the graph edges do not have a weight attribute a default weight of 1 will be used.

There may be more than one tree with the same minimum or maximum weight. See networkx.tree.recognition for more detailed definitions.

Isolated nodes with self-loops are in the tree as edgeless isolated nodes.

Examples