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<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">To add more information, there are 2 problems. The “original” is a MIP and “permutation” is a version of original that I changed the order of some rows and columns.<br>
<br>
The table below show the objective function in each version of SCIP.<br>
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<img width="286" height="85" style="width:2.975in;height:.8833in" id="Image_x0020_1" src="cid:image001.png@01DA5539.167C4270"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Thiago<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>De :</b> Thiago NOVAES <br>
<b>Envoyé :</b> jeudi 1 février 2024 17:44<br>
<b>À :</b> 'Peter Notebaert' <mail@peno.be>; s schnug <sascha.schnug@gmail.com><br>
<b>Cc :</b> scip@zib.de<br>
<b>Objet :</b> RE: [SCIP] Different results between 8.0.3 and 8.1.0<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Ok, that makes sense.<br>
<br>
But in another case, I found 72,313,267 as objective with 8.1.0 and 71,882,637 with 8.0.3.<br>
<br>
How can I found the source of this difference? <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Thiago,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">De :</span></b><span lang="EN-US"> Peter Notebaert <<a href="mailto:mail@peno.be">mail@peno.be</a>>
<br>
<b>Envoyé :</b> jeudi 1 février 2024 15:56<br>
<b>À :</b> s schnug <<a href="mailto:sascha.schnug@gmail.com">sascha.schnug@gmail.com</a>><br>
<b>Cc :</b> Thiago NOVAES <<a href="mailto:thiago.novaes@princeps.com">thiago.novaes@princeps.com</a>>;
<a href="mailto:scip@zib.de">scip@zib.de</a><br>
<b>Objet :</b> Re: [SCIP] Different results between 8.0.3 and 8.1.0<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal">Note that this is not only in scip but for any solver. <o:p></o:p></p>
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<p class="MsoNormal">Also the order in which the data is supplied can result in a different solution vector with the same objective value. For example providing the model via an lp model or via mps will most probably also have this effect.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Peter<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Thu, 1 Feb 2024 at 14:09, s schnug <<a href="mailto:sascha.schnug@gmail.com">sascha.schnug@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">from the perspective of the solver, it only matters to find an optimal (objective) solution which is feasible (given some tolerances).<o:p></o:p></p>
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<p class="MsoNormal">Which solution of those candidates is picked is not guaranteed (although deterministic).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">What you describe is completely natural!<o:p></o:p></p>
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<p class="MsoNormal">Every single change (e.g. heuristic priority weights; new heuristics) might lead to different result-vectors for many people (if we assume proven optimal result-status with the same objective).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">It's even worse: You might see different result-vectors by just changing your operating-system or hardware in general (cannot give guarantees about SCIP here).<o:p></o:p></p>
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<p class="MsoNormal">The mailing-list contained an interesting runs-different-during-simulation-in-valgrind example today!<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">See <a href="https://coral.ise.lehigh.edu/mip-2008/talks/danna.pdf" target="_blank">https://coral.ise.lehigh.edu/mip-2008/talks/danna.pdf</a> for some "related" background.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">You should never assume result-vectors being stable across solutions (and maybe OS/hardware).<o:p></o:p></p>
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<p class="MsoNormal">Sometimes, there is some additional modelling possible, which can express your expectation about those side-constraints (e.g. lexicographic-ordering). But often this hurts.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Greetings,<o:p></o:p></p>
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<p class="MsoNormal">Sascha<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">(not a SCIP dev; but a happy user)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Am Do., 1. Feb. 2024 um 13:19 Uhr schrieb Thiago NOVAES <<a href="mailto:thiago.novaes@princeps.com" target="_blank">thiago.novaes@princeps.com</a>>:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hello,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">The result of a MIP (1 binary, 0 integer, 0 implicit integer, 2751 continuous, 2452 constraints) is different between versions 8.0.3 and 8.1.0. Difference only
in the variables, not in the objective function.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Looking at the release notes for 8.0.4 and 8.1.0 I didn't find anything that justified the difference.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Could anyone help me understand this better? Is there no guarantee on variables between versions?
</span>I can share the .lp if it helps.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Best regards,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thiago<o:p></o:p></p>
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<p class="MsoNormal">_______________________________________________<br>
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<a href="https://listserv.zib.de/mailman/listinfo/scip" target="_blank">https://listserv.zib.de/mailman/listinfo/scip</a><o:p></o:p></p>
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<p class="MsoNormal">_______________________________________________<br>
Scip mailing list<br>
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<a href="https://listserv.zib.de/mailman/listinfo/scip" target="_blank">https://listserv.zib.de/mailman/listinfo/scip</a><o:p></o:p></p>
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