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147 lines
4.3 KiB
147 lines
4.3 KiB
/* glpios08.c (clique cut generator) */
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/***********************************************************************
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* This code is part of GLPK (GNU Linear Programming Kit).
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*
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* Copyright (C) 2008, 2013 Andrew Makhorin, Department for Applied
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* Informatics, Moscow Aviation Institute, Moscow, Russia. All rights
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* reserved. E-mail: <mao@gnu.org>.
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*
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* GLPK is free software: you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* GLPK is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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* License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GLPK. If not, see <http://www.gnu.org/licenses/>.
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***********************************************************************/
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#include "cfg.h"
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#include "env.h"
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#include "glpios.h"
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void *ios_clq_init(glp_tree *T)
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{ /* initialize clique cut generator */
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glp_prob *P = T->mip;
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CFG *G;
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int j, n1, n2;
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xprintf("Constructing conflict graph...\n");
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G = cfg_build_graph(P);
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n1 = n2 = 0;
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for (j = 1; j <= P->n; j++)
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{ if (G->pos[j])
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n1 ++;
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if (G->neg[j])
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n2++;
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}
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if (n1 == 0 && n2 == 0)
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{ xprintf("No conflicts found\n");
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cfg_delete_graph(G);
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G = NULL;
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}
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else
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xprintf("Conflict graph has %d + %d = %d vertices\n",
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n1, n2, G->nv);
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return G;
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}
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void ios_clq_gen(glp_tree *T, void *G_)
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{ /* attempt to generate clique cut */
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glp_prob *P = T->mip;
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int n = P->n;
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CFG *G = G_;
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int *pos = G->pos;
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int *neg = G->neg;
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int nv = G->nv;
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int *ref = G->ref;
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int j, k, v, len, *ind;
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double rhs, sum, *val;
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xassert(G->n == n);
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/* allocate working arrays */
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ind = talloc(1+n, int);
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val = talloc(1+n, double);
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/* find maximum weight clique in conflict graph */
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len = cfg_find_clique(P, G, ind, &sum);
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#ifdef GLP_DEBUG
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xprintf("len = %d; sum = %g\n", len, sum);
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cfg_check_clique(G, len, ind);
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#endif
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/* check if clique inequality is violated */
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if (sum < 1.07)
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goto skip;
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/* expand clique to maximal one */
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len = cfg_expand_clique(G, len, ind);
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#ifdef GLP_DEBUG
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xprintf("maximal clique size = %d\n", len);
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cfg_check_clique(G, len, ind);
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#endif
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/* construct clique cut (fixed binary variables are removed, so
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this cut is only locally valid) */
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rhs = 1.0;
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for (j = 1; j <= n; j++)
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val[j] = 0.0;
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for (k = 1; k <= len; k++)
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{ /* v is clique vertex */
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v = ind[k];
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xassert(1 <= v && v <= nv);
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/* j is number of corresponding binary variable */
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j = ref[v];
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xassert(1 <= j && j <= n);
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if (pos[j] == v)
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{ /* v corresponds to x[j] */
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if (P->col[j]->type == GLP_FX)
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{ /* x[j] is fixed */
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rhs -= P->col[j]->prim;
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}
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else
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{ /* x[j] is not fixed */
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val[j] += 1.0;
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}
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}
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else if (neg[j] == v)
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{ /* v corresponds to (1 - x[j]) */
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if (P->col[j]->type == GLP_FX)
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{ /* x[j] is fixed */
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rhs -= (1.0 - P->col[j]->prim);
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}
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else
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{ /* x[j] is not fixed */
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val[j] -= 1.0;
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rhs -= 1.0;
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}
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}
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else
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xassert(v != v);
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}
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/* convert cut inequality to sparse format */
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len = 0;
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for (j = 1; j <= n; j++)
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{ if (val[j] != 0.0)
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{ len++;
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ind[len] = j;
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val[len] = val[j];
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}
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}
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/* add cut inequality to local cut pool */
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glp_ios_add_row(T, NULL, GLP_RF_CLQ, 0, len, ind, val, GLP_UP,
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rhs);
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skip: /* free working arrays */
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tfree(ind);
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tfree(val);
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return;
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}
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void ios_clq_term(void *G_)
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{ /* terminate clique cut generator */
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CFG *G = G_;
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xassert(G != NULL);
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cfg_delete_graph(G);
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return;
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}
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/* eof */
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