Zoltan 2 Version 0.5
Zoltan2_AlgRCM.hpp
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00005 //   Zoltan2: A package of combinatorial algorithms for scientific computing
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00045 #ifndef _ZOLTAN2_ALGRCM_HPP_
00046 #define _ZOLTAN2_ALGRCM_HPP_
00047 
00048 #include <Zoltan2_GraphModel.hpp>
00049 #include <Zoltan2_OrderingSolution.hpp>
00050 #include <queue>
00051 
00052 
00056 
00057 
00058 namespace Zoltan2{
00059 
00060 template <typename Adapter>
00061 int AlgRCM(
00062   const RCP<GraphModel<Adapter> > &model, 
00063   const RCP<OrderingSolution<typename Adapter::gid_t,
00064                              typename Adapter::lno_t> > &solution,
00065   const RCP<Teuchos::ParameterList> &pl,
00066   const RCP<Teuchos::Comm<int> > &comm
00067 ) 
00068 {
00069   typedef typename Adapter::lno_t lno_t;
00070   typedef typename Adapter::gno_t gno_t;
00071   typedef typename Adapter::gid_t gid_t;
00072   typedef typename Adapter::scalar_t scalar_t;
00073 
00074   int ierr= 0;
00075 
00076   HELLO;
00077 
00078   // Check size of communicator: serial only.
00079   // TODO: Remove this test when RCM works on local graph.
00080   if (comm->getSize() > 1){
00081     throw std::runtime_error("RCM currently only works in serial.");
00082   }
00083 
00084   const size_t nVtx = model->getLocalNumVertices();
00085   lno_t *perm;
00086   perm = (lno_t *) (solution->getPermutationRCP().getRawPtr());
00087   for (size_t i=0; i<nVtx; i++){
00088     perm[i] = -1;
00089   }
00090 
00091   // Get local graph.
00092   ArrayView<const gno_t> edgeIds; 
00093   ArrayView<const lno_t> offsets;
00094   ArrayView<StridedData<lno_t, scalar_t> > wgts;
00095 
00096   // TODO: edgeIds should be of type lno_t for getLocalEdgeList. Needs revisit.
00097   //model->getLocalEdgeList(edgeIds, offsets, wgts); // BUGGY!
00098   // Use global graph for now. This only works in serial!
00099   ArrayView<const int> procIds;
00100   model->getEdgeList( edgeIds, procIds, offsets, wgts);
00101 
00102   //cout << "Debug: Local graph from getLocalEdgeList" << endl;
00103   //cout << "edgeIds: " << edgeIds << endl;
00104   //cout << "offsets: " << offsets << endl;
00105 
00106   // TODO: Find min-degree (or pseudo-peripheral) root vertex.
00107   lno_t root = 0;
00108 
00109   // Do BFS from root
00110   std::queue<lno_t> Q;
00111   size_t count = 0; // CM label, reversed later
00112   size_t next = 0;
00113 
00114   while (count < nVtx-1){ // Some vertex remains unlabelled
00115 
00116     // Label connected component starting at root
00117     Q.push(root);
00118     //cout << "Debug: perm[" << root << "] = " << count << endl;
00119     perm[root] = count++;
00120 
00121     while (Q.size()){
00122       // Get a vertex from the queue
00123       lno_t v = Q.front();
00124       Q.pop();
00125       //cout << "Debug: v= " << v << ", offsets[v] = " << offsets[v] << endl;
00126 
00127       // Add unmarked nbors to queue
00128       // TODO: If edge weights, sort nbors by decreasing weight,
00129       // TODO: Else, sort nbors by increasing degree
00130       for (lno_t ptr = offsets[v]; ptr < offsets[v+1]; ++ptr){
00131         lno_t nbor = edgeIds[ptr];
00132         if (perm[nbor] == -1){
00133           //cout << "Debug: perm[" << nbor << "] = " << count << endl;
00134           perm[nbor] = count++; // Label as we push on Q
00135           Q.push(nbor);
00136         }
00137       }
00138     }
00139 
00140     // Find an unmarked vertex, use as new root
00141     while ((next < nVtx) && (perm[next] != -1)) next++;
00142     root = next;
00143   }
00144 
00145   // Reverse labels for RCM
00146   bool reverse = true; // TODO: Make parameter
00147   if (reverse) {
00148     lno_t temp;
00149     for (size_t i=0; i < nVtx/2; ++i) {
00150       // Swap (perm[i], perm[nVtx-i])
00151       temp = perm[i];
00152       perm[i] = perm[nVtx-1-i];
00153       perm[nVtx-1-i] = temp;
00154     }
00155   }
00156 
00157   return ierr;
00158 }
00159 
00160 }
00161 #endif