Code for negative edge cycle with in a graph

[mukt...@gmail.com]

  Hello,
         I am working on complex network. I want to find all negative cycle or positive cycle within a graph ,
          i get function (negative_edge_cycle(g)) in negative cycle,but it returns true or false while i need to
         find all list and sum of weight of edges which involved make cycle.
         i am new in python can any one help me?

[Daniel Schult]

You might be able to tweak the code in the bellman ford algorithm (which is what negative_edge_cycle uses).  At line 742 there is the heart of the algorithm called

_bellman_ford_relaxation.

I'll also give my usual qualifier that it is highly unlikely that you really want all negative cycles (or all cycles). Because cycles can be combined to create other cycles and there are just too many possibilities. You probably want some sort of cycle basis that covers all the cycles only once. Then to create other cycles you combine those basis cycles. 

Finally, you can find a cycle basis using edge weights equal to 1 (using something like cycle_basis) and then go back and compute the cycle weights using the true weights. Not sure if that is what you really want though.

Good luck!

Dan

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