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<p>Hi Marc.</p>
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<p>Thanks for your support. I am using Gurobi as LP-solver. Scale of the coefficients should be fine, they are all between 1e2 and 1e6, however I have some Big-M's in my objective function that I can not get rid of. I am wondering why I run into stability issues
only when I solve my LP for some time (e.g., for a day). It seems to me that after some time my pricer generates columns that imply that issues. I will activate LP solver logging and see if Gurobi is giving me some hints.</p>
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<p>Regards</p>
<p>Christian</p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Von:</b> Scip <scip-bounces@zib.de> im Auftrag von Marc Pfetsch <pfetsch@mathematik.tu-darmstadt.de><br>
<b>Gesendet:</b> Freitag, 18. Dezember 2020 20:58<br>
<b>An:</b> scip@zib.de<br>
<b>Betreff:</b> Re: [SCIP] "Resolve instable" in SCIP statistics?</font>
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Hi Christian,<br>
<br>
the "resolve instable" indeed refers to the work that SCIP and the<br>
LP-solver try to obtain a numerically correct result. SCIP checks<br>
whether the solution returned by the solver is actually feasible. If<br>
this is not the case, then it tries to switch the LP-solver from dual to<br>
primal, tries to tighten the feasibility tolerance, starts from scratch<br>
(no warm start) etc.<br>
<br>
In your case, the LP-solver seems to struggle with the LP-relaxation.<br>
Which solver are you using?<br>
<br>
You can try to improve your model, e.g., by scaling or checking that you<br>
do not have very large coefficients together with very small ones in<br>
constraints or the coefficients. You can also check whether you have<br>
big-Ms in the model that you might be able to reduce. But first should<br>
probably turn on the output of the LP-solver to maybe get an idea of<br>
what is going wrong (parameter display/lpinfo).<br>
<br>
Best<br>
<br>
Marc<br>
<br>
<br>
<br>
On 18/12/2020 13:56, Franzen, Christian wrote:<br>
> Hi SCIP Team.<br>
> <br>
> <br>
> I am implementing a branch-and-price solver and for one of my benchmark<br>
> instances solving is significantly slower than for other instances. In<br>
> the statistics of SCIP is see the following output:<br>
> <br>
> <br>
> LP : Time Calls Iterations Iter/call <br>
> Iter/sec Time-0-It Calls-0-It ItLimit<br>
> primal LP : 39822.63 1350 22117847 22431.89 <br>
> 555.41 80.20 364<br>
> dual LP : 903.64 9 622937 69215.22 <br>
> 689.36 0.00 0<br>
> lex dual LP : 0.00 0 0 0.00 -<br>
> barrier LP : 0.00 0 0 0.00 <br>
> - 0.00 0<br>
> resolve instable : 32994.26 583 21004525 36028.34 636.61<br>
> diving/probing LP: 8.31 27 28543 1057.15 3436.36<br>
> strong branching : 0.00 0 0 0.00 <br>
> - - - 0<br>
> (at root node) : - 0 0 0.00 -<br>
> conflict analysis: 0.00 0 0 0.00 -<br>
> <br>
> I am not sure what these statistics tell me. Most of the time the LP<br>
> solver is struggeling with resolving any instability. What kind of<br>
> instability is meant here? Is this something related to numerical<br>
> issues? What can I do to solve that "issue"?<br>
> <br>
> <br>
> Regards<br>
> <br>
> Christian<br>
> <br>
> <br>
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> <br>
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