[Scip] scip reports optimal solution along with violated constraints

[Tobias Achterberg]

The strange thing in your output is that there are zeros in the 'cols' and 'rows' columns 
of the node log. So, I guess that something went wrong with the flags of the constraint 
creation.

Could you please recompile SCIP from scratch, and also recompile your code from scratch, 
making sure that the include path is consistent with the SCIP libraries?


Tobias


Martin Bergner wrote:
> Hi Tobias,
>
> I am using SCIP in the version 1.2.0.8
>
>> Is there anything strange in the SCIP output? For example, what does
>> presolving say about the size of the model? What numbers appear in the
>> node log, in particular the "rows" and
>> "cols" column? Is the model solved directly at the root node?
> No, it looks good, here is an excerpt for subproblem 1 first from the
> code, then from the command line:
>
> ----------8<----------8<----------8<----------8<----------
> presolving (2 rounds):
>   6 deleted vars, 0 deleted constraints, 0 tightened bounds, 0 added holes, 0 changed sides, 0 changed coefficients
>   0 implications, 0 cliques
> presolved problem has 51 variables (0 bin, 0 int, 0 impl, 51 cont) and 14 constraints
>
>   time | node  | left  |LP iter|LP it/n| mem |mdpt |frac |vars |cons |cols |rows |cuts |confs|strbr|  dualbound   | primalbound  |  gap
> t 0.0s|     1 |     0 |     0 |     - | 187k|   0 |   - |  51 |  14 |   0 |   0 |   0 |   0 |   0 |      --      | 0.000000e+00 | 100.00%
>    0.0s|     1 |     0 |     0 |     - | 187k|   0 |   - |  51 |  14 |   0 |   0 |   0 |   0 |   0 | 0.000000e+00 | 0.000000e+00 |   0.00%
>
> SCIP Status        : problem is solved [optimal solution found]
> Solving Time (sec) : 0.00
> Solving Nodes      : 1
> Primal Bound       : +0.00000000000000e+00 (3 solutions)
> Dual Bound         : +0.00000000000000e+00
> Gap                : 0.00 %
>    [linear]<c593>: -1<x58>[C] -1<x66>[C] -1<x74>[C] -1<x82>[C] -1<x90>[C] -1<x98>[C] -1<x106>[C] +1<x514>[C] == 0;
> violation: right hand side is violated by 74
> best solution is not feasible in original problem
> ----------8<----------8<----------8<----------8<----------
>
> Compare the command line with presolving turned off:
> ----------8<----------8<----------8<----------8<----------
> SCIP>  r prob_1.lp
> original problem has 57 variables (6 bin, 0 int, 0 impl, 51 cont) and 14 constraints
> SCIP>  o
>
> presolving:
> presolving (0 rounds):
>   0 deleted vars, 0 deleted constraints, 0 tightened bounds, 0 added holes, 0 changed sides, 0 changed coefficients
>   0 implications, 0 cliques
> presolved problem has 57 variables (6 bin, 0 int, 0 impl, 51 cont) and 14 constraints
>       14 constraints of type<linear>
> Presolving Time: 0.00
>
>   time | node  | left  |LP iter|LP it/n| mem |mdpt |frac |vars |cons |cols |rows |cuts |confs|strbr|  dualbound   | primalbound  |  gap
>    0.0s|     1 |     0 |    10 |     - | 221k|   0 |   4 |  57 |  14 |  57 |  14 |   0 |   0 |   0 | 4.625000e+00 |      --      |    Inf
> r 0.0s|     1 |     0 |    10 |     - | 222k|   0 |   - |  57 |  14 |  57 |  14 |   0 |   0 |   0 | 4.625000e+00 | 4.625000e+00 |   0.00%
>    0.0s|     1 |     0 |    10 |     - | 222k|   0 |   - |  57 |  14 |  57 |  14 |   0 |   0 |   0 | 4.625000e+00 | 4.625000e+00 |   0.00%
>
> SCIP Status        : problem is solved [optimal solution found]
> Solving Time (sec) : 0.01
> Solving Nodes      : 1
> Primal Bound       : +4.62500000000000e+00 (1 solutions)
> Dual Bound         : +4.62500000000000e+00
> Gap                : 0.00 %
> ----------8<----------8<----------8<----------8<----------
>
> The only differences are in the presolving. If I allow scip to presolve
> from the command line, it eliminates all variables and constraints. The
> objective function and solution, however, is correct either way from the
> command line.
>
> Regards,
> Martin
>
>