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# all_pairs_lowest_common_ancestor

all_pairs_lowest_common_ancestor(G, pairs=None)

  Return the lowest common ancestor of all pairs or the provided pairs

  Parameters:
    G NetworkX directed graph
    pairs iterable of pairs of nodes, optional (default: all pairs)

      The pairs of nodes of interest. If None, will find the LCA of all pairs of nodes.

  Yields:
    ((node1, node2), lca)2-tuple

      Where lca is least common ancestor of node1 and node2. Note that for the default case, the order of the node pair is not considered, e.g. you will not get both `(a, b)` and `(b, a)`

  Raises:
    NetworkXPointlessConcept

      If `G` is null.

    NetworkXError

      If `G` is not a DAG.

  See also

  `lowest_common_ancestor`

  Notes

  Only defined on non-null directed acyclic graphs.

  Examples

  The default behavior is to yield the lowest common ancestor for all possible combinations of nodes in `G`, including self-pairings:

      >>> G = nx.DiGraph([(0, 1), (0, 3), (1, 2)])
      >>> dict(nx.all_pairs_lowest_common_ancestor(G))
      {(0, 0): 0, (0, 1): 0, (0, 3): 0, (0, 2): 0, (1, 1): 1, (1, 3): 0, (1, 2): 1, (3, 3): 3, (3, 2): 0, (2, 2): 2}

  The pairs argument can be used to limit the output to only the specified node pairings:

      >>> dict(nx.all_pairs_lowest_common_ancestor(G, pairs=[(1, 2), (2, 3)]))
      {(1, 2): 1, (2, 3): 0}