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<font face="monospace">Hi Stefan,<br>
<br>
Sorry to bother you again. <br>
I’ve followed your instructions and created a .nl file with AMPL
and used the interactive shell. I managed to get a file .sol
containing the solution found after a certain time limit. I used
both the command "write solution filename.sol" and "write
amplsol". Then I included the .sol in AMPL but the displayed
solution seems to be not reasonable, as the variables assume
values out of their own bounds, and the OF is completely different
from and unreasonably much better than the one shown by SCIP.
There is likely an error in the assignment of the solution to the
corresponding variables: I suppose that the order of the variables
is confused and the values are misplaced while writing the .sol
file, but I am not able to understand where the problem basically
lies. <br>
<br>
Could you please help me?<br>
<br>
Thank you in advance</font><br>
<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 12/03/2021 18:02, Stefan Vigerske ha
scritto:<br>
</div>
<blockquote type="cite"
cite="mid:247d9e62-1ade-c412-6224-e7a2af305646@gams.com">Hi,
<br>
<br>
if SCIP solved with a different objective function than AMPL
(because SCIP treats very small numbers as 0, but AMPL doesn't),
then the primal bound reported in the SCIP log can be different
than the one calculated by AMPL.
<br>
<br>
Stefan
<br>
<br>
On 3/12/21 1:35 PM, Oreste Fecarotta wrote:
<br>
<blockquote type="cite">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>
<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 11/03/2021 17:53, Stefan Vigerske ha scritto:
<br>
<blockquote type="cite">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>
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