This documents an unmaintained version of NetworkX. Please upgrade to a maintained version and see the current NetworkX documentation.

Source code for networkx.generators.stochastic

#    Copyright (C) 2010-2013 by
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>
#    All rights reserved.
#    BSD license.
"""Functions for generating stochastic graphs from a given weighted directed

from __future__ import division

from networkx.classes import DiGraph
from networkx.classes import MultiDiGraph
from networkx.utils import not_implemented_for

__author__ = "Aric Hagberg <aric.hagberg@gmail.com>"
__all__ = ['stochastic_graph']

[docs]@not_implemented_for('undirected') def stochastic_graph(G, copy=True, weight='weight'): """Returns a right-stochastic representation of directed graph `G`. A right-stochastic graph is a weighted digraph in which for each node, the sum of the weights of all the out-edges of that node is 1. If the graph is already weighted (for example, via a 'weight' edge attribute), the reweighting takes that into account. Parameters ---------- G : directed graph A :class:`~networkx.DiGraph` or :class:`~networkx.MultiDiGraph`. copy : boolean, optional If this is True, then this function returns a new graph with the stochastic reweighting. Otherwise, the original graph is modified in-place (and also returned, for convenience). weight : edge attribute key (optional, default='weight') Edge attribute key used for reading the existing weight and setting the new weight. If no attribute with this key is found for an edge, then the edge weight is assumed to be 1. If an edge has a weight, it must be a a positive number. """ if copy: G = MultiDiGraph(G) if G.is_multigraph() else DiGraph(G) # There is a tradeoff here: the dictionary of node degrees may # require a lot of memory, whereas making a call to `G.out_degree` # inside the loop may be costly in computation time. degree = dict(G.out_degree(weight=weight)) for u, v, d in G.edges(data=True): if degree[u] == 0: d[weight] = 0 else: d[weight] = d.get(weight, 1) / degree[u] return G