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

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]
```