FromAdjacencyMatrix / FromAdjacencyLists - broken? Workaround?

*To*: mathgroup at smc.vnet.net*Subject*: [mg104192] FromAdjacencyMatrix / FromAdjacencyLists - broken? Workaround?*From*: Andrew <dr.a.graham at googlemail.com>*Date*: Thu, 22 Oct 2009 22:33:38 -0400 (EDT)

Hello group, This question seems to have been touched on in the past but I'm not sure if it has ever been definitively answered. I would be grateful for some advice! I have some data that I would like to explore. It concerns a set of directed graphs, without edge weights. The data comes to me as the corresponding asymmetric adjacency matrices. I can visualise the graphs directly using the native function GraphPlot. However, I would prefer to visualise them using ShowGraph from the Combinatorica package - but this requires that the adjacency matrix is converted to the Combinatorica graph format first. The trouble is that (for directed graphs at least), FromAdjacencyMatrix appears to be broken. Example: g = Cycle[3, Type -> Directed] (*construct a simple directed graph in Combinatorica graph format*) Edges[g] (*List of edges*) Vertices[g] (*List of vertices*) GraphOptions[g] (*Shows the graph options*) ShowGraph[g, VertexNumber -> True] /. x : Arrow[__] -> {Arrowheads[{{Automatic, 0.6}}], x} (*Visualises the graph with ShowGraph, using a workaround to place the arrowheads mid- edge, as suggested Apr 2 2008 by dh*) GraphPlot[g, VertexLabeling -> True, DirectedEdges -> True] (*Visualises the graph with GraphPlot - the same outcome*) mg = ToAdjacencyMatrix[g, Type -> Directed] (*Convert to adjacency matrix*) mg // TableForm (*Inspect - seems appropriate*) mg // MatrixForm (*Ditto*) GraphPlot[mg, VertexLabeling -> True, DirectedEdges -> True] (*Cannot plot directly with ShowGraph, but with GraphPlot the graph is still preserved at this stage*) g2 = FromAdjacencyMatrix[mg, Type -> Directed] (*Convert back to a graph*) Edges[g2] (*Oh dear. The direction of edge #3 has been reversed*) Vertices[g2] (*Vertices are preserved*) GraphOptions[g2] (*Graph options are preserved*) ShowGraph[g2, VertexNumber -> True] /. x : Arrow[__] -> {Arrowheads[{{Automatic, 0.6}}], x} GraphPlot[g2, VertexLabeling -> True, DirectedEdges -> True] (*And visualising the graph with both ShowGraph & GraphPlot it is no longer the same as the graph we started out with*) The problem seems to be with FromAdjacencyMatrix FromAdjacencyLists shows the same problem Is there something wrong with the code above, or are these functions truly broken? If they are broken, can anyone help with writing a function that will correctly turn a directed adjacency matrix into Combinatorica lists of edges & vertices? Finally, if these functions are broken, can they be fixed? I have otherwise found Combinatorica very easy to work with & would prefer to stick with it rather than native functions if possible. The Combinatorica book has recently been republished in paperback & I have found it very helpful. Many thanks Andrew Graham Dept of Neurology Addenbrooke's Hospital

**Follow-Ups**:**Re: Re: FromAdjacencyMatrix /***From:*Thomas Dowling <thomasgdowling@gmail.com>

**Re: FromAdjacencyMatrix / FromAdjacencyLists - broken?***From:*Thomas Dowling <thomasgdowling@gmail.com>