[Scip] Is possible that SCIP returns an infeasible solution as the best one

[Rostislav Stanek]

Dear SCIP community,
the problem has been solved and the bug fixed.
I would like to thank especially Michael Winkler form the ZIB who 
supported me via more private e-mails.
Best regards.
Rostislav Stanek


Dne 18.5.2013 13:10, Rostislav Stanek napsal(a):
> Dear SCIP community,
> I have one question: Is it possible that SCIP returns an infeasible
> solution as the best one. I use the function SCIPgetBestSol(SCIP *scip)
> to obtain the optimal solution. But this solution is not always
> feasible. In the doxygen documentation stays: “gets best feasible primal
> solution found [...], or NULL if no solution has been found or the
> candidate store is empty;”.
>
> Listing:
> time | node | left |LP iter|LP it/n| mem |mdpt |frac |vars |cons |cols
> |rows |cuts |confs|strbr| dualbound | primalbound | gap
> 3.2s| 1 | 0 | 867 | - | 41M| 0 | 10 |9203 | 193 |9203 | 162 | 0 | 30 |
> 10 | 2.613000e+04 | 2.735200e+04 | 4.68%
> 3.2s| 1 | 0 | 867 | - | 41M| 0 | 10 |9203 | 193 |9203 | 162 | 0 | 30 |
> 10 | 2.613000e+04 | 2.735200e+04 | 4.68%
> 3.3s| 1 | 0 | 874 | - | 41M| 0 | 20 |9203 | 193 |9203 | 166 | 4 | 30 |
> 10 | 2.613000e+04 | 2.735200e+04 | 4.68%
> 3.3s| 1 | 0 | 874 | - | 41M| 0 | 20 |9203 | 193 |9203 | 166 | 4 | 30 |
> 10 | 2.613000e+04 | 2.735200e+04 | 4.68%
> 3.3s| 1 | 2 | 874 | - | 41M| 0 | 20 |9203 | 193 |9203 | 166 | 4 | 30 |
> 27 | 2.613000e+04 | 2.735200e+04 | 4.68%
> f 4.1s| 49 | 49 | 1415 | 11.0 | 42M| 27 | - |9203 | 193 |9203 | 164 | 4
> | 30 | 409 | 2.613000e+04 | 2.620000e+04 | 0.27%
> * 4.7s| 95 | 91 | 1744 | 9.2 | 43M| 37 | - |9203 | 178 |9203 | 165 | 5 |
> 30 | 688 | 2.613000e+04 | 2.614400e+04 | 0.05%
> 4.8s| 100 | 94 | 1764 | 8.9 | 43M| 41 | - |9203 | 178 |9203 | 165 | 5 |
> 30 | 726 | 2.613000e+04 | 2.614400e+04 | 0.05%
> * 5.2s| 124 | 104 | 2030 | 9.3 | 43M| 58 | - |9203 | 178 |9203 | 165 | 5
> | 30 |1003 | 2.613000e+04 | 2.614100e+04 | 0.04%
> * 5.3s| 126 | 104 | 2036 | 9.2 | 44M| 59 | - |9203 | 178 |9203 | 165 | 5
> | 30 |1015 | 2.613000e+04 | 2.613600e+04 | 0.02%
> s 5.3s| 131 | 0 | 2095 | 9.3 | 43M| 60 | - |9203 | 178 |9203 | 165 | 5 |
> 30 |1022 | 2.613000e+04 | 2.612500e+04 | 0.02%
>
> SCIP Status : problem is solved [optimal solution found]
> Solving Time (sec) : 5.32
> Solving Nodes : 131 (total of 132 nodes in 2 runs)
> Primal Bound : +2.61250000000000e+04 (7 solutions)
> Dual Bound : +2.61250000000000e+04
> Gap : 0.00 %
>
> [...]
>
> violation: left hand side is violated by 5
>
> The primal bound gets smaller than the dual bound in the last step. And
> I am sure that a feasible solution exists. Do I understand something wrong?
> Thank you very much for response.
> Yours faithfully
> Rostislav Stanek
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