dag_longest_path#

dag_longest_path(G, weight='weight', default_weight=1, topo_order=None)[source]#

Returns the longest path in a directed acyclic graph (DAG).

If G has edges with weight attribute the edge data are used as weight values.

Parameters:

GNetworkX DiGraph: A directed acyclic graph (DAG)
weightstr, optional: Edge data key to use for weight
default_weightint, optional: The weight of edges that do not have a weight attribute
topo_order: list or tuple, optional: A topological order for G (if None, the function will compute one)

Returns:

list: Longest path

Raises:

NetworkXNotImplemented: If G is not directed

See also

dag_longest_path_length

Examples

>>> DG = nx.DiGraph([(0, 1, {'cost':1}), (1, 2, {'cost':1}), (0, 2, {'cost':42})])
>>> list(nx.all_simple_paths(DG, 0, 2))
[[0, 1, 2], [0, 2]]
>>> nx.dag_longest_path(DG)
[0, 1, 2]
>>> nx.dag_longest_path(DG, weight="cost")
[0, 2]

In the case where multiple valid topological orderings exist, topo_order can be used to specify a specific ordering:

>>> DG = nx.DiGraph([(0, 1), (0, 2)])
>>> sorted(nx.all_topological_sorts(DG))  # Valid topological orderings
[[0, 1, 2], [0, 2, 1]]
>>> nx.dag_longest_path(DG, topo_order=[0, 1, 2])
[0, 1]
>>> nx.dag_longest_path(DG, topo_order=[0, 2, 1])
[0, 2]