<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
</head>
<body>
<font face="monospace">Dear Stefan,<br>
thank you for your fast reply. If I understand, the behavior of
SCIP with small numbers (x=0 if -10^-9<=x<=10^-9), explains
why it differently performs as I use a different number to scale
the OF. <br>
Nevertheless, I do not understand why this implies that the primal
bound is different from the final solution. E.g., during the
calculation, it shows a primal bound equal to -1.54E-07; then
reaches the time limit; finally, the printed OF is -1.04E-07,
which is very close to the guess point, without significant
improvements.<br>
<br>
Thank you for your help,<br>
</font>
<div class="moz-signature">
<pre>Oreste Fecarotta
PhD in Hydraulic Engineering
Assistant Professor in Hydraulic Engineering
University of Naples "Federico II"
Via Claudio 21, 80125 Napoli (ITALY)
- ScopusID: <a href="https://www.scopus.com/authid/detail.uri?authorId=36503779200">36503779200</a>
- ORCID: <a href="https://orcid.org/0000-0003-0471-8821">0000-0003-0471-8821</a>
- WoSID: <a href="https://publons.com/researcher/1354138/oreste-fecarotta/">P-7250-2016</a>
- web: <a href="www.docenti.unina.it/oreste.fecarotta">Docenti unina</a>
- Ord.Ing.NA Sez.A 20328
- tel: +39-081-7683462
- fax: +39-081-1683456
</pre>
</div>
<div class="moz-cite-prefix">Il 11/03/2021 17:53, Stefan Vigerske ha
scritto:<br>
</div>
<blockquote type="cite"
cite="mid:955349cd-d528-5342-4217-de31ce624718@gams.com">Hi,
<br>
<br>
SCIP treats numbers within 1e-9 of zero as zero. If you divided
your objective by 1e12, this would mean that objective
coefficients that were within [-1000,1000] before are now treated
as 0 by SCIP.
<br>
<br>
I don't think that there is anything to automatically print the
best solution while solving or to write all solutions to a file at
the end, but if you let AMPL generate a .nl file and then run
scipampl on this .nl file with additional option -i, i.e.,
<br>
/path/to/scipampl /path/to/myproblem.nl -i
<br>
then you will get into the interactive shell of SCIP
(<a class="moz-txt-link-freetext" href="https://www.scipopt.org/doc/html/SHELL.php">https://www.scipopt.org/doc/html/SHELL.php</a>).
<br>
In the shell, there is a "display solutions" command that you can
use to print all solutions that were found after a solve to the
screen.
<br>
<br>
Stefan
<br>
<br>
On 3/11/21 12:24 PM, Oreste Fecarotta wrote:
<br>
<blockquote type="cite">Hi,
<br>
I'm using SCIP with AMPL, and I have a large problem involving
thousands of variables and contraints.
<br>
I found that I can get some good results
<br>
1) by setting heuristics to aggressive and
<br>
2) Dividing the objective function by a large number (let me say
10^12)
<br>
<br>
With my surprise, the improvement in the primal bound that is
shown during the calculation is lost as I print the OF value
once I reach the time limit. I cannot understand why this
happens. Furthermore, this does not happen if I divide the OF by
a smaller number (i.e. 10^6). Unfortunately, in the latter case,
I cannot get the same improvement in the solution.
<br>
<br>
Could you please help me?
<br>
Is there any option to print the best solution found during the
calculation?
<br>
Or to store the whole solution pool?
<br>
I found the option gams/dumpsolutions for GAMS, but I'm using
AMPL...
<br>
<br>
Thank you,
<br>
<br>
Oreste Fecarotta
<br>
PhD in Hydraulic Engineering
<br>
Assistant Professor in Hydraulic Engineering
<br>
University of Naples "Federico II"
<br>
Via Claudio 21, 80125 Napoli (ITALY)
<br>
- ScopusID:36503779200
<a class="moz-txt-link-rfc2396E" href="https://www.scopus.com/authid/detail.uri?authorId=36503779200"><https://www.scopus.com/authid/detail.uri?authorId=36503779200></a>
<br>
- ORCID:0000-0003-0471-8821
<a class="moz-txt-link-rfc2396E" href="https://orcid.org/0000-0003-0471-8821"><https://orcid.org/0000-0003-0471-8821></a>
<br>
- WoSID:P-7250-2016
<a class="moz-txt-link-rfc2396E" href="https://publons.com/researcher/1354138/oreste-fecarotta/"><https://publons.com/researcher/1354138/oreste-fecarotta/></a>
<br>
- web:Docenti unina
<<a class="moz-txt-link-abbreviated" href="http://www.docenti.unina.it/oreste.fecarotta">www.docenti.unina.it/oreste.fecarotta</a>>
<br>
- Ord.Ing.NA Sez.A 20328
<br>
- tel: +39-081-7683462
<br>
- fax: +39-081-1683456
<br>
<br>
Il 20/01/2021 09:31, Franzen, Christian ha scritto:
<br>
<blockquote type="cite">
<br>
Hi Ambros.
<br>
<br>
<br>
Thanks for your reponse and sorry for answering late. I have
"switched off" presolving by including no presolver plugins,
hence I only got the presolving code from the propagators and
constraint handlers. That seems to work properly. I started to
include one presolver plugin after the other and there seems
to be a problem with "domcol". It fixed a lot of variables and
afterwards my problem is reported to be unbounded. I did not
test all presolver plugins yet, but I will try to test all of
them by the end of this week. Any idea concerning "domcol"?
<br>
<br>
<br>
Regards
<br>
Christian
<br>
<br>
------------------------------------------------------------------------
<br>
*Von:* Scip <a class="moz-txt-link-rfc2396E" href="mailto:scip-bounces@zib.de"><scip-bounces@zib.de></a> im Auftrag von Ambros
Gleixner <a class="moz-txt-link-rfc2396E" href="mailto:gleixner@zib.de"><gleixner@zib.de></a>
<br>
*Gesendet:* Mittwoch, 13. Januar 2021 21:15
<br>
*An:* <a class="moz-txt-link-abbreviated" href="mailto:scip@zib.de">scip@zib.de</a>
<br>
*Betreff:* Re: [SCIP] After stopping pricing and doing
restart, model is becoming unbounded during presolve?
<br>
Hi Christian,
<br>
<br>
Strange indeed. Have you tried to turn off presolving? Does
it still
<br>
happen? Have you tried to successively activate individual
presolvers
<br>
to see when it starts failing?
<br>
<br>
Best,
<br>
Ambros
<br>
<br>
<br>
Am 04.01.21 um 17:10 schrieb Franzen, Christian:
<br>
> Hi Scip Team.
<br>
>
<br>
>
<br>
> Thanks to the help of Gregor, I managed to make SCIP stop
pricing after
<br>
> some iterations and doing a restart on the reduced master
without
<br>
> pricing. Unfortunately, I am facing some really strang
behaviour.
<br>
> Sometime it happens, that my model (for that I already
have found a
<br>
> feasible solution), is reported to be unbound. I wrote
the corresponding
<br>
> LP files before and after presolving to disk and I see
that some
<br>
> variable bounds vanished, which seems to be the reason
for the
<br>
> unboundness. Furthermore, some of the objective
coefficients changed
<br>
> their sign. Any ideas how or why that is happening during
presolving?
<br>
>
<br>
>
<br>
> Regards
<br>
>
<br>
> Christian
<br>
>
<br>
>
<br>
> P.S.: I attach the SCIP log for one of these runs.
<br>
>
<br>
>
<br>
> _______________________________________________
<br>
> Scip mailing list
<br>
> <a class="moz-txt-link-abbreviated" href="mailto:Scip@zib.de">Scip@zib.de</a>
<br>
> <a class="moz-txt-link-freetext" href="https://listserv.zib.de/mailman/listinfo/scip">https://listserv.zib.de/mailman/listinfo/scip</a>
<a class="moz-txt-link-rfc2396E" href="https://listserv.zib.de/mailman/listinfo/scip"><https://listserv.zib.de/mailman/listinfo/scip></a>
<br>
>
<br>
_______________________________________________
<br>
Scip mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Scip@zib.de">Scip@zib.de</a>
<br>
<a class="moz-txt-link-freetext" href="https://listserv.zib.de/mailman/listinfo/scip">https://listserv.zib.de/mailman/listinfo/scip</a>
<a class="moz-txt-link-rfc2396E" href="https://listserv.zib.de/mailman/listinfo/scip"><https://listserv.zib.de/mailman/listinfo/scip></a>
<br>
<br>
_______________________________________________
<br>
Scip mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Scip@zib.de">Scip@zib.de</a>
<br>
<a class="moz-txt-link-freetext" href="https://listserv.zib.de/mailman/listinfo/scip">https://listserv.zib.de/mailman/listinfo/scip</a>
<br>
</blockquote>
<br>
<br>
<br>
_______________________________________________
<br>
Scip mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Scip@zib.de">Scip@zib.de</a>
<br>
<a class="moz-txt-link-freetext" href="https://listserv.zib.de/mailman/listinfo/scip">https://listserv.zib.de/mailman/listinfo/scip</a>
<br>
<br>
</blockquote>
<br>
_______________________________________________
<br>
Scip mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Scip@zib.de">Scip@zib.de</a>
<br>
<a class="moz-txt-link-freetext" href="https://listserv.zib.de/mailman/listinfo/scip">https://listserv.zib.de/mailman/listinfo/scip</a>
<br>
</blockquote>
<br>
</body>
</html>