
From:  William Gordon Rutherdale 
Subject:  Re: [Helpglpk] Cannot get integer case to work 
Date:  Tue, 25 Aug 2009 09:09:02 0400 
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On 08/25/2009 08:41 AM, Andrew Makhorin wrote:
That's funny, I specifically issued the statementGlp_intopt requires an optimal solution to lp relaxation, i.e. in case of mip you need to call glp_simplex first and then call glp_intopt. control_params.presolve = GLP_ON; before calling glp_intopt(). My understanding from the documentation is that this would tell it to do the simplex presolve on its own. Furthermore, the trace it showed on the screen indicated that it had in fact found the LP solution already, before tackling the integer programming problem. Please see partial screen output below, from the original attempt. Does the "Crashing..." part mean anything bad? As a followup attempt I worked in a glp_simplex() call prior to the glp_intopt() call, just to see if that made a difference. In that scenario it gave the LP solution as the integer solution, with fractional values for x and y. I still haven't found a path that seems to work. Will Solving problem with integer constraints. ipp_basic_tech: 0 row(s) and 0 column(s) removed ipp_reduce_bnds: 2 pass(es) made, 2 bound(s) reduced ipp_basic_tech: 0 row(s) and 0 column(s) removed ipp_reduce_coef: 1 pass(es) made, 0 coefficient(s) reduced glp_intopt: presolved MIP has 2 rows, 2 columns, 4 nonzeros glp_intopt: 2 integer columns, none of which are binary Scaling... A: minaij = 2.000e+00 maxaij = 1.000e+01 ratio = 5.000e+00 Problem data seem to be well scaled Crashing... Size of triangular part = 2 Solving LP relaxation... * 0: obj = 0.000000000e+00 infeas = 0.000e+00 (0) * 3: obj = 5.508333333e+01 infeas = 0.000e+00 (0) OPTIMAL SOLUTION FOUND Integer optimization begins... + 3: mip = not found yet <= +inf (1; 0) + 4: >>>>> 5.300000000e+01 <= 5.300000000e+01 0.0% (3; 0) + 4: mip = 5.300000000e+01 <= tree is empty 0.0% (0; 5) INTEGER OPTIMAL SOLUTION FOUND result==0 z==0, x==0, y==0 
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