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95 lines
2.9 KiB
95 lines
2.9 KiB
2 years ago
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/*
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* Copyright(C) 1999-2020 National Technology & Engineering Solutions
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* of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
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* NTESS, the U.S. Government retains certain rights in this software.
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*
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* See packages/seacas/LICENSE for details
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*/
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#include "defs.h" // for FALSE, TRUE
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#include "structs.h" // for vtx_data
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/* Find a maximal matching in a graph using simple greedy algorithm. */
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/* Randomly permute vertices, and then have each select an unmatched */
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/* neighbor. */
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int maxmatch1(struct vtx_data **graph, /* array of vtx data for graph */
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int nvtxs, /* number of vertices in graph */
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int *mflag, /* flag indicating vtx selected or not */
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int using_ewgts /* are edge weights being used? */
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)
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{
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extern int HEAVY_MATCH; /* choose heavy edges in matching? */
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float ewgt_max; /* largest edge weight seen so far */
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int *jptr; /* loops through integer arrays */
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int vtx; /* vertex to process next */
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int neighbor; /* neighbor of a vertex */
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int nmerged; /* number of edges in matching */
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int matched; /* is a vertex matched yet? */
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int jsave; /* best matching edge found so far */
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int i, j; /* loop counters */
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double drandom(void);
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/* Initialize mflag array. */
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jptr = mflag;
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for (i = nvtxs; i; i--) {
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*(++jptr) = 0;
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}
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nmerged = 0;
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/* Select random starting point in list of vertices. */
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vtx = 1 + drandom() * nvtxs;
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if (!using_ewgts || !HEAVY_MATCH) { /* Choose first neighbor */
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for (i = nvtxs; i; i--) {
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if (mflag[vtx] == 0) { /* Not already matched. */
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/* Select first free edge. */
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matched = FALSE;
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for (j = 1; !matched && j < graph[vtx]->nedges; j++) {
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neighbor = graph[vtx]->edges[j];
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if (mflag[neighbor] == 0) {
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mflag[vtx] = neighbor;
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mflag[neighbor] = vtx;
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matched = TRUE;
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nmerged++;
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}
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}
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}
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if (++vtx > nvtxs) {
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vtx = 1;
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}
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}
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}
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else { /* Choose heavy edge neighbor */
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for (i = nvtxs; i; i--) {
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if (mflag[vtx] == 0) { /* Not already matched. */
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/* Select heaviest free edge. */
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jsave = 0;
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ewgt_max = 0;
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for (j = 1; j < graph[vtx]->nedges; j++) {
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neighbor = graph[vtx]->edges[j];
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if (mflag[neighbor] == 0 && graph[vtx]->ewgts[j] > ewgt_max) {
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ewgt_max = graph[vtx]->ewgts[j];
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jsave = j;
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}
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}
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if (jsave > 0) {
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neighbor = graph[vtx]->edges[jsave];
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mflag[vtx] = neighbor;
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mflag[neighbor] = vtx;
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nmerged++;
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}
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}
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if (++vtx > nvtxs) {
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vtx = 1;
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}
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}
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}
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return (nmerged);
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}
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