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From: | Heinrich Schuchardt |
Subject: | Re: Regression between 4.61 and 4.65 for problems which can be preprocessed to almost nothing |
Date: | Mon, 13 Jul 2020 18:56:11 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
On 13.07.20 17:20, Domingo Alvarez Duarte wrote: > Hello Peter ! > > Till glpk 4.64 this error does not happen, I'm looking through the code > and think that the real fix is to prevent to solve the problem if the > presolver eliminated all columns or rows. > > Cheers ! > The presolver may find an integer optimal solution. Then the solver stops with: INTEGER OPTIMAL SOLUTION FOUND BY MIP PREPROCESSOR Currently this is only reached if the transformed equation system has zero columns and zero rows (src/draft/glpapi09.c, line 328). In the example the presolved equation system has 0 columns and 1 row. Why is this row is not active and therefore not eliminated in npp_process_prob() (src/npp/npp5.c:651)? Best regards Heinrich
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