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<p class="MsoNormal"><span style="color:#1F497D">Hi Gregor,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thank you for your useful instruction.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">When i tried with PYTHONHASHSEED=0, it generated exactly the same results.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thank you all,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="color:windowtext;mso-fareast-language:TR">From:</span></b><span lang="EN-US" style="color:windowtext;mso-fareast-language:TR"> Scip <scip-bounces@zib.de>
<b>On Behalf Of </b>Gregor Hendel<br>
<b>Sent:</b> Wednesday, October 3, 2018 6:33 PM<br>
<b>To:</b> scip@zib.de<br>
<b>Subject:</b> Re: [SCIP] SCIP produces different results for the same problem instance<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Dear Tufan,<br>
<br>
we are actually making an effort to keep SCIP deterministic, so you should see the same solution after every call on the same problem. A time limit might lead to different results, but this does not seem to be the case here.<br>
<br>
I tend to say you got "Pythoned" here.<br>
<br>
My best guess, as I have no other information how you invoke the problem solve, is that you use dictionaries<br>
somewhere in the problem creation. Now, depending on the version, Python's internal hashing is nondeterministic,<br>
see also <a href="https://stackoverflow.com/questions/14956313/why-is-dictionary-ordering-non-deterministic">
here</a>. The same would be true for Java, I suppose. If you loop over the keys() of a dictionary, the order<br>
is different every time you run, effectively generating a different permutation of your problem's columns and rows, which may affect the performance of the MIP solver and also specific solution values may be different between runs, but of course not the objective
value of an optimal solution.<br>
<br>
The link I posted contains a link to a solution to the problem using a PYHASHSEED environment variable, which I haven't verified.<br>
<br>
Let us know if this is the source of, and solution to, your problem,<br>
Gregor<br>
<br>
<span style="font-size:12.0pt;mso-fareast-language:TR"><o:p></o:p></span></p>
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<p class="MsoNormal">Am 03.10.2018 um 13:09 schrieb Tufan BAYDEMİR:<o:p></o:p></p>
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<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">I’m using pyscipopt interface within Python to solve a MIP problem.
<o:p></o:p></p>
<p class="MsoNormal">I run the same code without making any changes and obtain different optimal solutions.<o:p></o:p></p>
<p class="MsoNormal">The objective function value is the same for all solutions. <o:p>
</o:p></p>
<p class="MsoNormal">But value of the decision variables are always different ie. The program ganarates alternative optimal solutions in each subsequent run.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">How can I insure that i get the same solution?<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Regards<o:p></o:p></p>
<p class="MsoNormal">Tufan<o:p></o:p></p>
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<o:p></o:p></span></p>
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