Re: Finding paths in graphs
- To: mathgroup at smc.vnet.net
- Subject: [mg72527] Re: [mg72524] Finding paths in graphs
- From: John Dickmann <jqd at mit.edu>
- Date: Fri, 5 Jan 2007 01:42:04 -0500 (EST)
OT,
this works for me, courtesy of Andrezj Koslowski from a 1996 posting,
modified to improve speed some.
If there's anybody else out there who has a faster way to do this,
I'd really like to see it.
<< DiscreteMath`Combinatorica`
<< DiscreteMath`GraphPlot`;
AllPaths[g_Graph, {a_, b_}] :=
Module[{s = {a}, done, npath = 0, e = ToAdjacencyLists[g], x,
v, ind, n = V[g], c = 0}, ind = Table[1, {n}];
While[Length[s] > 0, v = Last[s];
done = False;
While[ind[[v]] <= Length[e[[v]]] && !
done, If[! MemberQ[s, (x = e[[v, ind[[v]]++]])], done = True]];
If[done, s = {s, x}; s = Flatten[s]; If[(x ==
b), npath = npath + 1;(*If[npath == c +
1000, Print["npath: ", npath]; c = npath];*)If[Length[s] >= 0,
s =
Drop[s, -1]]],
If[Length[s] > 0, s = Drop[s, -1]]; ind[[v]] =
1]]; Print["Start node: ", a, "; End node: ", b, ";
Number of Paths: ", npath]]
john
On Jan 4, 2007, at 7:00 AM, OT wrote:
> Hi all,
>
> I have a big oriented graph in a Mathematica notebook, described as a
> list of rule (i.e the graph is something like {1->2 , 1->3, 2-
> >3, ... })
> and I want to find all the path from vertex 'a' to vertex 'b'...
>
> How can I do that ? The function ShortestPath doesn't work on graphs
> defined in this way, and moreover this function only return one of the
> shortest paths, while I'm looking for all the existing paths...
>
> thanks,
> OT
>
John Q. Dickmann
Research Assistant
Lean Aerospace Initiative
Massachusetts Institute of Technology
Bldg 41-205
77 Massachusetts Ave.
Cambridge, MA 02139
jqd at mit.edu
401-225-3511