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<p>Hi, I was also running into a similar problem after upgrading to
scip 8.0.3.</p>
<p>I am using benders decomposition to solver rather large
instances. After I updated scip 7 to scip 8.0.3 some infeasible
instances are getting solved to "optimality" but when checking the
proposed solution it was obviously not even feasible for the
solved instance.</p>
<p>Attached you can find an example instance on which this problem
occurred. The orig.lp is the non decomposed formulation with whom
the infeasibility is correctly detected, and the master.lp and
sub__.lp files contain the respective parts of the decomposed
formulation. Also attached are some log files from the solution
process.<br>
</p>
<p>This could either be due to vast numerical issues or a bug within
the scip code, but this didn't happened when using scip 7.0.3.<br>
</p>
<p>Regards,</p>
<p>Lisa-Marie Manke<br>
</p>
<div class="moz-cite-prefix">On 24.04.23 15:06, Barry Hurley wrote:<br>
</div>
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cite="mid:4b240e04-3c89-461c-8a66-6fbc61d0a347@Spark">
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<div dir="auto">Hi, we were looking at upgrading from SCIP
version 7 to version 8.0.3 but one of our unit-tests is
catching a regression where SCIP appears to be producing a
sub-optimal solution and claiming optimality. We are using
SCIP via the LP file interface, the files to reproduce are
attached. problem.lp is the original problem, and
problem-forced-solution.lp extends this with an additional
constraint called `FORCED_SOLUTION` to force the optimal
solution. Also including the parameter settings used.<br>
<br>
The solution should have an optimal objective value of 115,
but SCIP version 8.0.3 is incorrectly producing a solution
with objective value 120, even with gap zero. The solution is
valid, just sub-optimal. There is one difference in the
assignment, binary variable X_2__1_ has an objective
coefficient of 15, but SCIP 8 is incorrectly assigning binary
variable X_3__1_ to 1 instead even though its objective
coefficient is higher at 20.<br>
<br>
Would you have any advice if there is something we are using
SCIP incorrectly, or if this is a legitimate bug? Other than
the attached parameter settings, we are using the pre-built
binaries on ubuntu x86. Many thanks in advance.</div>
</div>
<div name="messageSignatureSection"><br>
<div class="matchFont">Regards,<br>
Barry Hurley</div>
</div>
<br>
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<pre class="moz-signature" cols="72">--
Lisa-Marie Manke, M.Sc.
Technische Universität Carolo-Wilhelmina zu Braunschweig
Institut für Mathematische Optimierung | AIP
Universitätsplatz 2 | Mühlenpfortstr. 23
38106 Braunschweig
Cluster of Excellence Sustainable and Energy-Efficient Aviation (SE²A)
Hermann-Blenk-Str. 42
38108 Braunschweig</pre>
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