Re: new Graph function + combinatorica: various problems

*To*: mathgroup at smc.vnet.net*Subject*: [mg116404] Re: new Graph function + combinatorica: various problems*From*: Yaroslav Bulatov <yaroslavvb at gmail.com>*Date*: Sun, 13 Feb 2011 05:50:12 -0500 (EST)*References*: <ij2v05$7uu$1@smc.vnet.net>

I first asked about dealing with Combinatorica conflicts 2 months ago. Since then there were several discussions on stackoverflow site on combining the functionalities result of which is the following strategy which I have used for the last month without encountering any conflicts: Basically use system Graph for everything, use "Graph" to refer to System graph and "Combinatorica`Graph" to refer to Combinatorica Graph. Whenever Combinatorica function is needed, write a wrapper that converts object to Combinatorica`Graph, calls Combinatorica function, then converts the result back to System Graph if needed. This requires Combinatorica to be not on on ContextPath. Because functions like GraphUtilities`ToCombinatoricaGraph add Combinatorica to ContextPath on each call, use $Post to remove Combinatorica from ContextPath after each evaluation. Also, because Combinatorica redefines "System`Element" which breaks another package I use, I load Combinatorica using "Block[{Element},Needs["Combinatorica`"]]". GraphUtilities package shadows some built-ins, so its helpful to keep GraphUtilities out of ContextPath and refer to those functions explicitly, ie GraphUtilities`EdgeList I execute the following at the start of each session: $Post = ($ContextPath = DeleteCases[$ContextPath, "Combinatorica`" | "GraphUtilities`"]; #) &; Block[{Element}, Needs["Combinatorica`"]; Needs["GraphUtilities`"]] Here's an example of a wrapper that takes list of edges and weights, calls Combinatorica's MaximumSpanningTree and returns list of edges in the tree (* uses combinatorica to find maximum weight spanning tree *) maxWeightSpanTree[edges_List,weights_List]:=Module[{nums,nodes,nums2nodes= ,nodes2nums,numEdges,combgraph,wCombGraph,combTree}, Block[{Element},Needs["Combinatorica`"]]; $ContextPath=DeleteCases[$ContextPath,"Combinatorica`"]; nodes=Union[fl1@edges]; nums=Range[Length@nodes]; nums2nodes=Thread[nums->nodes]; nodes2nums=Reverse/@nums2nodes; numEdges=edges/.nodes2nums; combGraph=Combinatorica`FromUnorderedPairs[numEdges]; wCombGraph=Combinatorica`SetEdgeWeights[combGraph,numEdges,weights]; combTree=Combinatorica`MaximumSpanningTree[wCombGraph]; Combinatorica`ToUnorderedPairs[combTree]/.nums2nodes ]; On Feb 11, 1:20 am, Cupidio <andreatacche... at gmail.com> wrote: > Hi, > I'm experiencing some problems in combining the functionalities of > combinatorica and the built-in functions for graphs. > > In fact loading combinatorica shadows the built-in Graph function, and > makes its use impossible. But while I need some of the functions in > the combinatorica package (minimum/maximum spanning tree), i prefer > the graphic and "lexical" representation of the built-in Graph[]. > > How do I "save" Graph[] when I load combinatorica, or how can I make > it come back? > > Also (and this looks weird!), when i use ToCombinatoricaGraph[] (in > GraphUtilites package) to convert a graph, the resulting object can be > processed by MaximumSpanningTree[], yielding a correct result, but not > by MinimumSpanningTree[] which returns something like: > > MinimumSpanningTree[-Graph:<14,8,Directed>-] > > ...not even a combinatorica graph object. > > Thanks for your help!