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Diffstat (limited to 'glpk-5.0/src/intopt/clqcut.c')
| -rw-r--r-- | glpk-5.0/src/intopt/clqcut.c | 132 |
1 files changed, 132 insertions, 0 deletions
diff --git a/glpk-5.0/src/intopt/clqcut.c b/glpk-5.0/src/intopt/clqcut.c new file mode 100644 index 0000000..5077b51 --- /dev/null +++ b/glpk-5.0/src/intopt/clqcut.c @@ -0,0 +1,132 @@ +/* clqcut.c (clique cut generator) */ + +/*********************************************************************** +* This code is part of GLPK (GNU Linear Programming Kit). +* Copyright (C) 2008-2016 Free Software Foundation, Inc. +* Written by Andrew Makhorin <mao@gnu.org>. +* +* GLPK is free software: you can redistribute it and/or modify it +* under the terms of the GNU General Public License as published by +* the Free Software Foundation, either version 3 of the License, or +* (at your option) any later version. +* +* GLPK is distributed in the hope that it will be useful, but WITHOUT +* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public +* License for more details. +* +* You should have received a copy of the GNU General Public License +* along with GLPK. If not, see <http://www.gnu.org/licenses/>. +***********************************************************************/ + +#include "cfg.h" +#include "env.h" +#include "prob.h" + +/*********************************************************************** +* NAME +* +* glp_clq_cut - generate clique cut from conflict graph +* +* SYNOPSIS +* +* int glp_clq_cut(glp_prob *P, glp_cfg *G, int ind[], double val[]); +* +* DESCRIPTION +* +* This routine attempts to generate a clique cut. +* +* The cut generated by the routine is the following inequality: +* +* sum a[j] * x[j] <= b, +* +* which is expected to be violated at the current basic solution. +* +* If the cut has been successfully generated, the routine stores its +* non-zero coefficients a[j] and corresponding column indices j in the +* array locations val[1], ..., val[len] and ind[1], ..., ind[len], +* where 1 <= len <= n is the number of non-zero coefficients. The +* right-hand side value b is stored in val[0], and ind[0] is set to 0. +* +* RETURNS +* +* If the cut has been successfully generated, the routine returns +* len, the number of non-zero coefficients in the cut, 1 <= len <= n. +* Otherwise, the routine returns a non-positive value. */ + +int glp_clq_cut(glp_prob *P, glp_cfg *G, int ind[], double val[]) +{ int n = P->n; + int *pos = G->pos; + int *neg = G->neg; + int nv = G->nv; + int *ref = G->ref; + int j, k, v, len; + double rhs, sum; + xassert(G->n == n); + /* find maximum weight clique in conflict graph */ + len = cfg_find_clique(P, G, ind, &sum); +#ifdef GLP_DEBUG + xprintf("len = %d; sum = %g\n", len, sum); + cfg_check_clique(G, len, ind); +#endif + /* check if clique inequality is violated */ + if (sum < 1.07) + return 0; + /* expand clique to maximal one */ + len = cfg_expand_clique(G, len, ind); +#ifdef GLP_DEBUG + xprintf("maximal clique size = %d\n", len); + cfg_check_clique(G, len, ind); +#endif + /* construct clique cut (fixed binary variables are removed, so + this cut is only locally valid) */ + rhs = 1.0; + for (j = 1; j <= n; j++) + val[j] = 0.0; + for (k = 1; k <= len; k++) + { /* v is clique vertex */ + v = ind[k]; + xassert(1 <= v && v <= nv); + /* j is number of corresponding binary variable */ + j = ref[v]; + xassert(1 <= j && j <= n); + if (pos[j] == v) + { /* v corresponds to x[j] */ + if (P->col[j]->type == GLP_FX) + { /* x[j] is fixed */ + rhs -= P->col[j]->prim; + } + else + { /* x[j] is not fixed */ + val[j] += 1.0; + } + } + else if (neg[j] == v) + { /* v corresponds to (1 - x[j]) */ + if (P->col[j]->type == GLP_FX) + { /* x[j] is fixed */ + rhs -= (1.0 - P->col[j]->prim); + } + else + { /* x[j] is not fixed */ + val[j] -= 1.0; + rhs -= 1.0; + } + } + else + xassert(v != v); + } + /* convert cut inequality to sparse format */ + len = 0; + for (j = 1; j <= n; j++) + { if (val[j] != 0.0) + { len++; + ind[len] = j; + val[len] = val[j]; + } + } + ind[0] = 0, val[0] = rhs; + return len; +} + +/* eof */ |