Hi,
I'm looking for an algorithm which computes the Minimum cut in a *directed*, weighted graph. All weights are positive, and the graph does not contain self loops. In the jgrapht package, there exists a Stoer Wagner implementation which computes the minimum cut in an undirected graph. I need the equivalent for a directed graph.
Jgrapht contains an algorithm for computing the minimum s-t cut in a directed graph, but this would require me to invoke the algorithm for every s-t pair, which is way to expensive. Any suggestion is welcome: 1. Do you know an algorithm/paper/book which describes such an algorithm. 2. Do you know a implementation of such an algorithm, preferably in java. Say for example that you have two vertices, a and b, and two arcs: (a,b) with capacity 4 and (b,a) with capacity 2. Then the minimum cut would be to partition the vertices into two sets, S and T, such that the max flow from S to T equals the minimum cut. For this example, the solution would be: S={b}, T={a}, max flow: 2.
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Hello Joris, The Min Cut is indeed a also a Max Flow problem. For this you can use the Ford Fulkerson algorithm. Here are some slides that you might need to read before you actually do the implementation: http://www.cs.princeton.edu/courses/archive/spr04/cos226/lectures/maxflow.4up.pdf
I don't know if jgraph has it but it might because it is one of the fundamental algorithms in Network Flow. I would respectfully advise that you understand the theory very well before you do the coding. When you do, you might find yourself designing a very neat algorithm and make a discovery. Hopefully you will be generous it with the rest of us ;)
Good luck! -Ahmed On Tue, Oct 1, 2013 at 3:18 PM, Joris Kinable <[hidden email]> wrote:
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Hi, Thanks for all the replies. @Ahmed: I think you missed my point. You are talking about the standard max flow min cut algorithm for a given s and t. I was asking for an algorithm which computes the global min cut, i.e. the min cut for *all* (s,t) pairs in the graph. Using the standard Ford Fulkerson algorithm is way to slow to do that. FYI: last year I implemented this algorithm, and shared it with the Jgrapht community (see my implementation: MinSourceSinkCut) :). For this I used the Edmonds-Karp implementation.
@Luc: Thanks for the suggestion. For this project I prefer however a solution which does not require a solver. I think I found the solution. Hao and Orlin, A Faster Algorithm for Finding the Minimum Cut in a Directed Graph (1994) have proposed an efficient solution for my problem. Implementation details can be found in: Cherkassky, Goldberg, On Implementing push-relabel method for the maximum flow problem (1994). Although I couldn't find any Java implementations, a C implementation can be found here: http://www.zib.de/en/services/web-services/mathprog/mincut.html
see: global-dir.tar.Z It is easy to modify the code and if gives exactly what I need: a partitioning of the nodes in S and T, and the cut weight. If I find some time in the future, I might consider implementing this in jgrapht as well.
Thanks for the suggestions, Joris On Tue, Oct 1, 2013 at 3:44 PM, Ahmed Abdeen Hamed <[hidden email]> wrote:
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Found this thread 2 years after it was originally created... This is something I also need. I tried the link you posted regarding the C code, but it isn't available anymore...
Do you by any chance still have some kind of sample code for this? I'm looking for a quick solution and this seems promising. Thanks! Keshet |
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