-------- Original Message -------- Subject: Re: [Bug-glpk] Bug in glpk 4.21? Date: Sat, 1 Sep 2007 01:54:28 +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?

The bug appears if the constant term of the objective is non-zero either originally or due to fixing some columns at non-zero value by the mip preprocessor. In my previous post I just commented out the corresponding fragment leading to wrong results. To fix the bug in a correct way please replace lines 748 and 751 (the routine ios_preprocess_node, file src/glpios02.c): 748: L[0] = -DBL_MAX, U[0] = mip->mip_obj; 751: L[0] = mip->mip_obj, U[0] = +DBL_MAX; by the following ones: 748: L[0] = -DBL_MAX, U[0] = mip->mip_obj - mip->c0; 751: L[0] = mip->mip_obj - mip->c0, U[0] = +DBL_MAX; Please note that these changes will appear in the next version of the package. 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