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"""Unary operations on graphs"""
import networkx as nx
__all__ = ["complement", "reverse"]
def complement(G):
"""Returns the graph complement of G.
Parameters
----------
G : graph
A NetworkX graph
Returns
-------
GC : A new graph.
Notes
-----
Note that `complement` does not create self-loops and also
does not produce parallel edges for MultiGraphs.
Graph, node, and edge data are not propagated to the new graph.
Examples
--------
>>> G = nx.Graph([(1, 2), (1, 3), (2, 3), (3, 4), (3, 5)])
>>> G_complement = nx.complement(G)
>>> G_complement.edges() # This shows the edges of the complemented graph
EdgeView([(1, 4), (1, 5), (2, 4), (2, 5), (4, 5)])
"""
R = G.__class__()
R.add_nodes_from(G)
R.add_edges_from(
((n, n2) for n, nbrs in G.adjacency() for n2 in G if n2 not in nbrs if n != n2)
)
return R
def reverse(G, copy=True):
"""Returns the reverse directed graph of G.
Parameters
----------
G : directed graph
A NetworkX directed graph
copy : bool
If True, then a new graph is returned. If False, then the graph is
reversed in place.
Returns
-------
H : directed graph
The reversed G.
Raises
------
NetworkXError
If graph is undirected.
Examples
--------
>>> G = nx.DiGraph([(1, 2), (1, 3), (2, 3), (3, 4), (3, 5)])
>>> G_reversed = nx.reverse(G)
>>> G_reversed.edges()
OutEdgeView([(2, 1), (3, 1), (3, 2), (4, 3), (5, 3)])
"""
if not G.is_directed():
raise nx.NetworkXError("Cannot reverse an undirected graph.")
else:
return G.reverse(copy=copy)
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