Python, Generating Random Graphs with Graph-tool

Question

So I'm trying to generate a random directed graph such that each vertex has 3 in-nodes and 1 outnode. But graph tool seems to be getting stuck in the deg_sampler() function.

from graph_tool.all import *

def deg_sampler():
    return 1,2
g = random_graph(1000,deg_sampler,verbose=True)

I get this error after running the code

adding vertices: 1000 of 1000 (100%)
fixing average degrees. Total degree difference: 1000^CTraceback (most recent call last):
  File "code.py", line 6, in <module>
    g = random_graph(1000,deg_sampler,verbose=True)
  File "/usr/lib/python2.7/dist-packages/graph_tool/generation/__init__.py", line 384, in random_graph
    _get_rng(), verbose, True)
  File "/usr/lib/python2.7/dist-packages/graph_tool/generation/__init__.py", line 379, in <lambda>
    sampler = lambda i: deg_sampler()
KeyboardInterrupt

Were you trying to copy text somewhere? Hitting Ctrl-C kills whatever is running in Python. That would be why you see "KeyboardInterrupt" at the bottom there. — Cody Piersall
– Cody Piersall, Commented Dec 3, 2015 at 17:52
I mean I would quit the program after about 30 minutes. Should it take that long to generate the nodes? — Karmanya Aggarwal
– Karmanya Aggarwal, Commented Dec 3, 2015 at 19:09

Tiago Peixoto · Accepted Answer · 2015-12-04 09:24:20Z

1

The degree sampler function should return the in- and out-degrees of the nodes. In your implementation, each node has an in-degree of 1 and out-degree of 2. It is, of course, impossible to construct a graph with this degree sequence, since the average in- and out-degrees must identical. This is why the algorithm gets stuck in the "fixing average degrees" phase.

answered Dec 4, 2015 at 9:24

Tiago Peixoto

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