/// Rewire a bipartite graph. Keeps node degrees as is but randomly rewires the
/// edges. Use this function to generate a random graph with the same degree
/// sequence as the OrigGraph.
/// See: On the uniform generation of random graphs with prescribed degree
/// sequences by R. Milo, N. Kashtan, S. Itzkovitz, M. E. J. Newman, U. Alon
/// URL: http://arxiv.org/abs/cond-mat/0312028
PBPGraph GenRewire(const PBPGraph& OrigGraph, const int& NSwitch, TRnd& Rnd) {
const int Nodes = OrigGraph->GetNodes();
const int Edges = OrigGraph->GetEdges();
PBPGraph GraphPt = TBPGraph::New();
TBPGraph& Graph = *GraphPt;
Graph.Reserve(Nodes, -1);
TExeTm ExeTm;
// generate a graph that satisfies the constraints
printf("Randomizing edges (%d, %d)...\n", Nodes, Edges);
TIntPrSet EdgeSet(Edges);
for (TBPGraph::TNodeI NI = OrigGraph->BegLNI(); NI < OrigGraph->EndLNI(); NI++) {
const int NId = NI.GetId();
for (int e = 0; e < NI.GetOutDeg(); e++) {
EdgeSet.AddKey(TIntPr(NId, NI.GetOutNId(e))); } // edges left-->right
Graph.AddNode(NI.GetId(), true); } // left nodes
for (TBPGraph::TNodeI NI = OrigGraph->BegRNI(); NI < OrigGraph->EndRNI(); NI++) {
Graph.AddNode(NI.GetId(), false); } // right nodes
IAssert(EdgeSet.Len() == Edges);
// edge switching
uint skip=0;
for (uint swps = 0; swps < 2*uint(Edges)*uint(NSwitch); swps++) {
const int keyId1 = EdgeSet.GetRndKeyId(Rnd);
const int keyId2 = EdgeSet.GetRndKeyId(Rnd);
if (keyId1 == keyId2) { skip++; continue; }
const TIntPr& E1 = EdgeSet[keyId1];
const TIntPr& E2 = EdgeSet[keyId2];
TIntPr NewE1(E1.Val1, E2.Val2), NewE2(E2.Val1, E1.Val2);
if (NewE1!=NewE2 && NewE1.Val1!=NewE1.Val2 && NewE2.Val1!=NewE2.Val2 && ! EdgeSet.IsKey(NewE1) && ! EdgeSet.IsKey(NewE2)) {
EdgeSet.DelKeyId(keyId1); EdgeSet.DelKeyId(keyId2);
EdgeSet.AddKey(TIntPr(NewE1));
EdgeSet.AddKey(TIntPr(NewE2));
} else { skip++; }
if (swps % Edges == 0) {
printf("\r %uk/%uk: %uk skip [%s]", swps/1000u, 2*uint(Edges)*uint(NSwitch)/1000u, skip/1000u, ExeTm.GetStr());
if (ExeTm.GetSecs() > 2*3600) { printf(" *** Time limit!\n"); break; } // time limit 2 hours
}
}
printf("\r total %uk switchings attempted, %uk skiped [%s]\n", 2*uint(Edges)*uint(NSwitch)/1000u, skip/1000u, ExeTm.GetStr());
for (int e = 0; e < EdgeSet.Len(); e++) {
Graph.AddEdge(EdgeSet[e].Val1, EdgeSet[e].Val2); }
return GraphPt;
}
