[SCIP] question on a warning

Fri Oct 27 17:12:18 CEST 2023

Hi Domnik,

I've worked out what's going on here and it's not a problem with SCIP. I had some constraint handlers of my own for which I had not implemented the copy methods. So when a heuristic made a copy for a subSCIP some constraints were missing and so we got primal solutions suggested which should not have been.

After implementing the missing copy methods this problem went away.

Thanks for your input,

James

James Cussens
Room MVB 3.26
School of Computer Science, University of Bristol
Phone: +44 (0)117 455 8723
https://jcussens.github.io/
Funded PhDs available in Bristol in the following areas: Data Science<http://www.bristol.ac.uk/cdt/compass/>, Interactive AI<http://www.bristol.ac.uk/cdt/interactive-ai/>, Cyber Security<http://www.bristol.ac.uk/cdt/cyber-security/> or Digital Health<http://www.bristol.ac.uk/cdt/digital-health/>.
________________________________
From: Kamp, Dominik <Dominik.Kamp at uni-bayreuth.de>
Sent: 01 August 2023 17:26
To: James Cussens <james.cussens at bristol.ac.uk>
Cc: scip at zib.de <scip at zib.de>
Subject: Re: [SCIP] question on a warning

Hello James,

you are right. Since the objective value from the warning does not correspond to the main objective value, the warning must be thrown by a subscip. These warnings can be triggered due to numerics but there is also the chance that you have found a bug. Therefore, we would be very glad if you could share the corresponding instance with us (or file a bug report), so that we can get to the bottom of this potential issue.

Best regards,

Dominik

> Am 01.08.2023 um 18:03 schrieb James Cussens <james.cussens at bristol.ac.uk>:
>
> Hi all,
>
> I am getting the following warning:
>
>   time | node  | left  |LP iter|LP it/n|mem/heur|mdpt |vars |cons |rows |cuts |sepa|confs|strbr|  dualbound   | primalbound  |  gap   | compl.
>   0.0s|     1 |     0 |    39 |     - |  1118k |   0 |  20 |  36 |  63 |  30 | 31 |   1 |   0 |-1.804449e+02 | 0.000000e+00*|    Inf | unknown
>   0.0s|     1 |     0 |    40 |     - |  1118k |   0 |  20 |  36 |  64 |  31 | 32 |   1 |   0 |-1.802198e+02 | 0.000000e+00*|    Inf | unknown
>   0.0s|     1 |     0 |    41 |     - |  1124k |   0 |  20 |  36 |  65 |  32 | 33 |   1 |   0 |-1.801160e+02 | 0.000000e+00*|    Inf | unknown
>   0.1s|     1 |     2 |    41 |     - |  1128k |   0 |  20 |  36 |  65 |  32 | 34 |   1 |  15 |-1.800907e+02 | 0.000000e+00*|    Inf | unknown
> r 0.1s|    15 |    14 |    57 |   1.1 |rounding|  14 |  20 |  36 |  65 |  33 |  0 |   1 |  42 |-1.758398e+02 |-1.151438e+01 |1427.13%| unknown
> r 0.1s|    16 |    15 |    65 |   1.6 |rounding|  15 |  20 |  36 |  65 |  33 |  0 |   1 |  45 |-1.758398e+02 |-1.604484e+01 | 995.93%| unknown
> * 0.1s|    17 |    14 |    66 |   1.6 |    LP  |  16 |  20 |  36 |  65 |  33 |  1 |   1 |  45 |-1.758398e+02 |-2.039660e+01 | 762.10%| unknown
> r 0.1s|    24 |    17 |    78 |   1.6 |rounding|  16 |  20 |  36 |  66 |  35 |  0 |   1 |  50 |-1.758398e+02 |-2.640592e+01 | 565.91%| unknown
> * 0.1s|    34 |    21 |    95 |   1.6 |    LP  |  17 |  20 |  36 |  69 |  39 |  1 |   1 |  54 |-1.758398e+02 |-2.719577e+01 | 546.57%| unknown
> * 0.1s|    37 |    22 |    99 |   1.6 |    LP  |  18 |  20 |  36 |  70 |  40 |  1 |   1 |  54 |-1.758398e+02 |-6.270300e+01 | 180.43%| unknown
> r 0.2s|    57 |    30 |   144 |   1.8 |rounding|  18 |  20 |  36 |  72 |  54 |  1 |   1 |  61 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>   0.2s|   100 |    63 |   235 |   2.0 |  1345k |  18 |  20 |  36 |  69 |  73 |  2 |   1 |  69 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>   0.3s|   200 |   159 |   480 |   2.2 |  1845k |  18 |  20 |  36 |  71 | 149 |  2 |   1 |  71 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
> WARNING: Dual bound 69.0721 is larger than the objective of the primal solution 68.1511. The solution might not be optimal.
>   0.5s|   300 |   253 |   758 |   2.4 |  2248k |  18 |  20 |  36 |  76 | 226 |  1 |   1 |  71 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>   0.6s|   400 |   351 |  1029 |   2.5 |  2670k |  18 |  20 |  36 |  73 | 312 |  1 |   1 |  71 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>  time | node  | left  |LP iter|LP it/n|mem/heur|mdpt |vars |cons |rows |cuts |sepa|confs|strbr|  dualbound   | primalbound  |  gap   | compl.
>   0.7s|   500 |   443 |  1254 |   2.4 |  2799k |  18 |  20 |  36 |  70 | 367 |  1 |   1 |  71 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>   0.8s|   600 |   537 |  1467 |   2.4 |  3062k |  18 |  20 |  36 |  70 | 411 |  1 |   3 |  71 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>   1.0s|   700 |   633 |  1696 |   2.4 |  3247k |  18 |  20 |  36 |  70 | 470 |  1 |   3 |  71 |-1.758398e+02 |-6.485425e+01 | 171.13%| unknown
>
> SCIP Status        : solving was interrupted [time limit reached]
>
> The solutions I am getting are fine and I have no obvious errors, but I am curious as to what might have generated the warning. Perhaps it comes from some subscip run by a heuristic since the dual bound the warning mentions (69.0721) is some distance from that of the main problem ( -1.758398e+02). Can anyone explain what might be happening here; perhaps this indicates some problem I have not yet noticed.
>
> James
>
> James Cussens
> Room MVB 3.26
> Dept of Computer Science, University of Bristol
> Phone: +44 (0)117 455 8723
> https://jcussens.github.io/
> Funded PhDs available in Bristol in the following areas: Data Science, Interactive AI, Cyber Security or Digital Health.
> _______________________________________________
> Scip mailing list
> Scip at zib.de
> https://listserv.zib.de/mailman/listinfo/scip

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