[SCIP] SCIP detected infeasibility for feasible problem

[Hans Mittelmann]

Hi,

as the instructions on the solver webpage say, the command file can contain AMPL commands such as
option presolve 0;

Hans

> On Sep 11, 2019, at 8:28 AM, Stefan Vigerske <stefan at math.hu-berlin.de> wrote:
> 
> 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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