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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m solving set cover problems with SCIP 6.0.0. I have one instance where SCIP prints<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> [linear] <c_276>: <x_1013>[B] (-0) +<x_1019>[B] (-0) +<x_1021>[B] (-0) +<x_1131>[B] (-0) +<x_1139>[B] (-0) +<x_1142>[B] (-0) +<x_1301>[B] (-0) +<x_1302>[B] (-0) +<x_1317>[B] (-0) +<x_1318>[B] (-0) +<x_1322>[B] (+0) +<x_1323>[B] (+0) +<x_1324>[B]
(-0) +<x_1354>[B] (-0) +<x_1446>[B] (-0) +<x_1449>[B] (-0) +<x_1450>[B] (-0) +<x_1451>[B] (-0) +<x_1452>[B] (-0) +<x_1617>[B] (-0) +<x_1621>[B] (+0) +<x_1622>[B] (-0) +<x_1623>[B] (-0) +<x_1624>[B] (-0) +<x_1625>[B] (-0) +<x_1626>[B] (+0) +<x_1627>[B] (-0)
+<x_1820>[B] (+0) +<x_1952>[B] (+0) >= 1;<o:p></o:p></p>
<p class="MsoNormal">;<o:p></o:p></p>
<p class="MsoNormal">violation: left hand side is violated by 1<o:p></o:p></p>
<p class="MsoNormal">best solution is not feasible in original problem<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">SCIPgetStatus returns <span style="font-size:9.5pt;font-family:Consolas;color:darkslategray">
SCIP_STATUS_OPTIMAL.</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For some reason this error is not reproducible with LP or MPS files – most probably due to slight loss of numeric precision of the objective coefficients.
<o:p></o:p></p>
<p class="MsoNormal">Therefore I attached a small C++ problem that reproduces the issue.
<o:p></o:p></p>
<p class="MsoNormal">After compiling setcover.cpp you can run <o:p></o:p></p>
<p class="MsoNormal">./setcover sets.csv<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Unfortunatetly the programm requires boost for splitting strings – sorry for that.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For my understanding there is either a bug involved or the presolver is turning a (as far as I can see) numerically stable MIP into something unstable. CBC solves this MIP without issues.<o:p></o:p></p>
<p class="MsoNormal">Obvious workaround would be to check the constraint violation and try a second run with the presolver turned of…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Tobias<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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