Spanning Tree  Category  pgRouting Manual (3.4)
Spanning Tree  Category
A spanning tree of an undirected graph is a tree that includes all the vertices of G with the minimum possible number of edges.
For a disconnected graph, there there is no single tree, but a spanning forest, consisting of a spanning tree of each connected component.
Characteristics:

It’s implementation is only on undirected graph.

Process is done only on edges with positive costs.

When the graph is connected

The resulting edges make up a tree


When the graph is not connected,

Finds a minimum spanning tree for each connected component.

The resulting edges make up a forest.

See Also
Indices and tables