Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.9/dist-packages/networkx/generators/stochastic.py: 47%

1"""Functions for generating stochastic graphs from a given weighted directed 

2graph. 

3 

4""" 

5 

6import networkx as nx 

7from networkx.classes import DiGraph, MultiDiGraph 

8from networkx.utils import not_implemented_for 

9 

10__all__ = ["stochastic_graph"] 

11 

12 

13@not_implemented_for("undirected") 

14@nx._dispatch(edge_attrs="weight") 

15def stochastic_graph(G, copy=True, weight="weight"): 

16 """Returns a right-stochastic representation of directed graph `G`. 

17 

18 A right-stochastic graph is a weighted digraph in which for each 

19 node, the sum of the weights of all the out-edges of that node is 

20 1. If the graph is already weighted (for example, via a 'weight' 

21 edge attribute), the reweighting takes that into account. 

22 

23 Parameters 

24 ---------- 

25 G : directed graph 

26 A :class:`~networkx.DiGraph` or :class:`~networkx.MultiDiGraph`. 

27 

28 copy : boolean, optional 

29 If this is True, then this function returns a new graph with 

30 the stochastic reweighting. Otherwise, the original graph is 

31 modified in-place (and also returned, for convenience). 

32 

33 weight : edge attribute key (optional, default='weight') 

34 Edge attribute key used for reading the existing weight and 

35 setting the new weight. If no attribute with this key is found 

36 for an edge, then the edge weight is assumed to be 1. If an edge 

37 has a weight, it must be a positive number. 

38 

39 """ 

40 if copy: 

41 G = MultiDiGraph(G) if G.is_multigraph() else DiGraph(G) 

42 # There is a tradeoff here: the dictionary of node degrees may 

43 # require a lot of memory, whereas making a call to `G.out_degree` 

44 # inside the loop may be costly in computation time. 

45 degree = dict(G.out_degree(weight=weight)) 

46 for u, v, d in G.edges(data=True): 

47 if degree[u] == 0: 

48 d[weight] = 0 

49 else: 

50 d[weight] = d.get(weight, 1) / degree[u] 

51 return G