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/* ckcnf.c (check for CNF-SAT problem instance) */
/***********************************************************************
* This code is part of GLPK (GNU Linear Programming Kit).
* Copyright (C) 2010-2016 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 "env.h"
#include "prob.h"
int glp_check_cnfsat(glp_prob *P)
{ /* check for CNF-SAT problem instance */
int m = P->m;
int n = P->n;
GLPROW *row;
GLPCOL *col;
GLPAIJ *aij;
int i, j, neg;
#if 0 /* 04/IV-2016 */
if (P == NULL || P->magic != GLP_PROB_MAGIC)
xerror("glp_check_cnfsat: P = %p; invalid problem object\n",
P);
#endif
/* check columns */
for (j = 1; j <= n; j++)
{ col = P->col[j];
/* the variable should be binary */
if (!(col->kind == GLP_IV && col->type == GLP_DB &&
col->lb == 0.0 && col->ub == 1.0))
return 1;
}
/* objective function should be zero */
if (P->c0 != 0.0)
return 2;
for (j = 1; j <= n; j++)
{ col = P->col[j];
if (col->coef != 0.0)
return 3;
}
/* check rows */
for (i = 1; i <= m; i++)
{ row = P->row[i];
/* the row should be of ">=" type */
if (row->type != GLP_LO)
return 4;
/* check constraint coefficients */
neg = 0;
for (aij = row->ptr; aij != NULL; aij = aij->r_next)
{ /* the constraint coefficient should be +1 or -1 */
if (aij->val == +1.0)
;
else if (aij->val == -1.0)
neg++;
else
return 5;
}
/* the right-hand side should be (1 - neg), where neg is the
number of negative constraint coefficients in the row */
if (row->lb != (double)(1 - neg))
return 6;
}
/* congratulations; this is CNF-SAT */
return 0;
}
/* eof */
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