<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Dear Saleh,<br>
<br>
this is indeed a bit strange. <br>
<br>
There is probably a numerical problem. For starters, you can use
presolving, but avoid multiaggregations by<br>
setting the two boolean parameters "presolving/donotaggr" and
"presolving/donotmultaggr" to TRUE in your scip2. They are often the
reason for numerical troubles in the original space.<br>
<br>
Unfortunately, you have optimized out some of the relevant
information to help you, such as the type and violation of the
constraint that is violated.<br>
<br>
Two questions: <br>
1. I assume that if you do *not* disable presolving in the original
SCIP, the bug is not triggered?<br>
2. If the problem is a simple MIP problem, have you tried to write
out the transformed problems of both SCIPs? You could write them in
lp-format, which is very readable for small instances, and check
what has happened to the violated constraint after presolving in the
problem copy.<br>
<br>
To do so, use <br>
<br>
SCIP_CALL( SCIPpresolve(scip2) );<br>
<a class="code"
href="https://scip.zib.de/doc-6.0.0/html/group__GlobalProblemMethods.php#gada41a57fc5a464ad565763d24e588d3a">SCIP_CALL(
SCIPwriteTransProblem</a>(scip2, "presolvedprob.lp", "lp", false)
)<br>
<br>
Maybe one of my guesses gets you started already,<br>
Gregor<br>
<br>
<br>
<div class="moz-cite-prefix">Am 02.11.18 um 17:58 schrieb M. Far.:<br>
</div>
<blockquote type="cite"
cite="mid:CAGhf1zJuR1PQBEnoAfstes0dK70EQhD1emcuqC9Lvmy6-wAyew@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div>Hi</div>
<div>I am working on a simple MILP problem in
SCIP's c++ interface using CPLEX as the LP
solver.</div>
I have to disable presolving in my original
problem 'scip'. So I have:<br>
</div>
<div dir="ltr">SCIP_CALL( SCIPsetPresolving(scip,
SCIP_PARAMSETTING_OFF, true) );</div>
<div>after creating scip. Then, I need to solve a
copy of the problem by creating a second problem
'scip2':</div>
<div>SCIP* scip2;</div>
<div>SCIP_CALL( SCIPcreate(&scip2) );<br>
SCIP_CALL( SCIPcopyOrig(scip, scip2, nullptr,
nullptr, "copyProb", false, false, nullptr) );<br>
SCIP_CALL( SCIPsetIntParam(scip2,
"display/verblevel", 2) );</div>
<div><br>
</div>
<div>And I can turn on presolving procedure in
this problem. So I have:<br>
</div>
<div>`SCIP_CALL( SCIPsetPresolving(scip2,
SCIP_PARAMSETTING_DEFAULT, true) );`<br>
</div>
<div dir="ltr">
<div><br>
</div>
<div>Next, I want to add the solution of scip2
as an initial feasible solution to the
original problem. Hence:</div>
<div>```</div>
<div>SCIP_CALL( SCIPsolve(scip2) );<br>
auto sol2 = SCIPgetBestSol(scip2);<br>
SCIP_Bool stored;<br>
SCIP_CALL( SCIPaddSolFree(scip, &sol2,
&stored) );</div>
<div>```<br>
</div>
<div>However, when I solve the original scip by
calling `SCIPsolve(scip)`, I get the following
message in the output:</div>
<div>```<br>
</div>
<div>violation: right hand side is violated by
<a_number><br>
all 1 solutions given by solution candidate
storage are infeasible</div>
<div>```<br>
</div>
<div>Next, it ignores the solution, solves the
problem, and finds an "optimal solution" which
is inferior to sol2 (hence, not optimal
indeed).</div>
<div><br>
</div>
<div>I understand that something may be wrong
with the transformation. But I do not know how
to fix this.<br>
</div>
<div>(OS: Linux 4.15, SCIP ver.: 6.0.0, CPLEX
ver.: 12.8.0, gcc ver.: 7.3.0)<br>
</div>
<div><br>
</div>
<div>Bests,<br>
<div dir="ltr"
class="m_-1887873641005988722gmail-m_-4202621538027297685m_8836857469212455087m_-4500597847004404067gmail_signature">
<div dir="ltr"><br>
</div>
</div>
</div>
<div>Saleh<br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
Scip mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Scip@zib.de">Scip@zib.de</a>
<a class="moz-txt-link-freetext" href="https://listserv.zib.de/mailman/listinfo/scip">https://listserv.zib.de/mailman/listinfo/scip</a>
</pre>
</blockquote>
<br>
</body>
</html>