-------- Original Message -------- Subject: Re: [Bug-glpk] Bug in glpk 4.21? Date: Sat, 1 Sep 2007 00:12:19 +0400 From: Andrew Makhorin <mao@gnu.org> Reply-To: Andrew Makhorin <mao@gnu.org> To: Roberto Bagnara <bagnara@cs.unipr.it> CC: bug-glpk@gnu.org References: <10376349.20070831204809@gnu.org>

For the attached testcase, we obtain that

$ glpsol p0033.mps --max -o output.gomory --gomory

gives an optimum of 5201, while

$ glpsol p0033.mps --max -o output.intopt --intopt

gives an optimum of 5131. The optimum 5201 is confirmed by a completely different MIP solver. Does this behavior indicate there is a bug somewhere?

Thank you very much for your bug report. The bug appears only in 4.21 in the mip preprocessor (which is part of the routine glp_intopt). To fix the bug please replace the fragment in the routine ios_preprocess_node (file src/glpios02.c) between #if 0 and #else by the corresponding fragment between #else and #endif as follows: /* determine original row bounds */ L = xcalloc(1+m, sizeof(double)); U = xcalloc(1+m, sizeof(double)); #if 0 switch (mip->mip_stat) { case GLP_UNDEF: L[0] = -DBL_MAX, U[0] = +DBL_MAX; break; case GLP_FEAS: switch (mip->dir) { case GLP_MIN: L[0] = -DBL_MAX, U[0] = mip->mip_obj; break; case GLP_MAX: L[0] = mip->mip_obj, U[0] = +DBL_MAX; break; default: xassert(mip != mip); } break; default: xassert(mip != mip); } #else L[0] = -DBL_MAX, U[0] = +DBL_MAX; #endif for (i = 1; i <= m; i++) { L[i] = glp_get_row_lb(mip, i); U[i] = glp_get_row_ub(mip, i); } /* determine original column bounds */ and then compile the package as usual. Andrew Makhorin -- Prof. Roberto Bagnara Computer Science Group Department of Mathematics, University of Parma, Italy http://www.cs.unipr.it/~bagnara/ mailto:bagnara@cs.unipr.it