[SCIP] SCIP detected infeasibility for feasible problem

[Stefan Vigerske]

Hi,

I think these messages are from the AMPL presolver, not from SCIP.
In SCIP, numbers below 1e-9 are actually considered to be 0, often.

I don't know if you can turn off AMPL presolver (put "option presolve 
0;" somewhere or run AMPL with -P) via NEOS, though.

Stefan

On 9/11/19 4:26 PM, angelika.wiegele at aau.at wrote:
> Dear SCIP team,
> 
> via NEOS, I tried to solve a QP (100 integer variables, 300 quadratic 
> constraints) and SCIP returned: infeasible.
> 
> However, the problem *is* feasible.
> I found another way to get a feasible solution. Then I simply fixed in 
> the model-file the variables to the values of this solution, and SCIP 
> told me:
> 
> ***SCIP-AMPL***
> 
> presolve, constraint Con128:
>      all variables eliminated, but upper bound = -4.54747e-12 < 0
> presolve, constraint Con158:
>      all variables eliminated, but lower bound = 7.27596e-12 > 0
> presolve, constraint Con34:
>      all variables eliminated, but upper bound = -1.81899e-12 < 0
> presolve, constraint Con101:
>      all variables eliminated, but lower bound = 2.67164e-11 > 0
> presolve, constraint Con137:
>      all variables eliminated, but lower bound = 1.22782e-11 > 0
> Infeasible constraints determined by presolve.
> 
> 
> The numbers (in the solution) are "nice" in a sense that many of them 
> are zero and the non-zeros are integers in the range -100,..,100.
> 
> Question: how can I tell SCIP that 1e-11 can be considered as 0?
> 
> Best regards,
> Angelika
> 
> 
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