[SCIP] SCIP speed-up for .LP files

[Pierre Le Bodic]

Hi Marcus,

I gave a try to your problem. Using scip 5.0.1 and gurobi 8.0.0 as the LP
solver, I get a feasible solution in less than a second. Log attached.
Please let me know if you can't replicate this.

Kind regards,
Pierre

On 15 June 2018 at 08:38, Ambros Gleixner <gleixner at zib.de> wrote:

> Hi Marcus,
>
> 28456 variables are in general not particularly large, but for hard
> problems, also medium-sized instances can become very difficult.
>
> Gurobi is known to be stronger than SCIP, but it could be that with the
> right parameters also SCIP can solve the instances.  As a starter try to
> change emphasis settings, one or more of
>
> set presolving emphasis aggressive
> set separating emphasis {off,fast,aggressive}
> set heuristics emphasis aggressive
> set emphasis {feasibility,optimality,hardlp}
>
> and/or look at the statistics via "display statistics" to find expensive
> and unsuccessful plugins to be deactivated.
>
> But giving more detailed advice here is difficult without seeing the
> instance.  You can send me a larger, problematic instance of your model as
> a personal message, and I will try to find the time to look at it.
>
> Best,
> Ambros
>
>
>
>
>
> Am 14.06.2018 um 23:21 schrieb Marcus Garvie:
>
>> Hi everyone,
>>
>> this is my first post, so please understand that my knowledge of SCIP is
>> low!
>>
>> I have been solving some large binary linear programming problems with no
>> objective function. I solve .LP files using a terminal to issue the
>> commands on my Mac. The .LP files are automatically generated, with e.g.
>> the attached format.
>>
>> The only commands I issue are
>>
>> SCIP> read test.lp
>> SCIP> optimize test.lp
>>
>> The problem is that for very large problems (e.g. 28456 variables) the
>> solver seems to be running forever (> 2 days)! I tried the same problem in
>> Gurobi and it gave me the correct solution in 15 minutes. (I’m wanting to
>> use SCIP because it has some easy options for giving me all feasible
>> solutions, while Gurobi does not).
>>
>> I also tried the problem in CPLEX, but it has some limitations on the
>> length of the variable names (Error  1464) so I’m a little stuck if I want
>> multiple solutions for large problems.
>>
>> Any advice would be appreciated.
>>
>> Marcus.
>>
>> PS I only know how to problems in the  .LP format!
>>
>>
>>
>> ________________________________
>> Marcus R Garvie
>> Associate Professor
>> Rm 552 MacNaughton Bldg
>> Dept. of Math & Stats
>> University of Guelph
>> Guelph, ON Canada N1G 2W1
>> Tel. 519-824-4120 ext 53409
>> Email. _mgarvie at uoguelph.ca_ <mailto:mgarvie at uoguelph.ca>
>>
>>
>>
>>
>>
>> _______________________________________________
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>> Scip at zib.de
>> https://listserv.zib.de/mailman/listinfo/scip
>>
>>
> --
> Ambros Gleixner, Research Group Mathematical Optimization Methods at Zuse
> Institute Berlin, http://www.zib.de/gleixner
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