[Scip] Solving opb instances + initial solutions

[Marc Pfetsch]

Dear Luigi,

as far as I know, you cannot enter solutions in the OPB format.

The best way to tell SCIP about the solutions would be to create a file 
(something like <filename>.sol) for each instance that contains values 
for the variables. The format is easy - for your examle below:

objective value:   1
x2                 1   (obj:1)
x4                 1   (obj:0)

Zero variables are left out. I suppose that it is easy to modify your 
heuristic in order to output such a file. In the SCIP command line, you 
can then read the solution from the file.


By the way: The instances such as the one below could lead to troubles 
in SCIP, since big coefficients like "12345678901234567890" are likely 
to cause numerical problems (the instance below does not cause problems, 
though). In particular, SCIP can in general not solve the BIGINT 
instances from the Pseudo-Boolean competitions.

Best

Marc



On 20.01.2012 16:51, Luigi Malagò wrote:
> hello mailing list,
> right now i'm solving non linear pseudo-boolean functions f, which are
> parsed from the OPB format, e.g.
>
> * #variable= 5 #constraint= 4
> *
> * this is a dummy instance
> *
> min: 1 x2 -1 x3 ;
> 1 x1 +4 x2 -2 x5 >= 2;
> -1 x1 +4 x2 -2 x5 >= +3;
> 12345678901234567890 x4 +4 x3 >= 10;
> * an equality constraint
> 2 x2 +3 x4 +2 x1 +3 x5 = 5;
>
> (take from the http://www.cril.univ-artois.fr/PB10/format.pdf )
>
> i would like to speed up the solver, since i have (from some heuristic)
> a candidate optima solution for each instance
>
> i am minimizing f and i would like like to provide an upper bound for it
> (my candidate solutio from the heuristic).
>
> can i insert it the OPB file?
> if not, in case I re-implement the opb_reader, which method should i
> call to provide the solver with an initial solution?
> i checked the documentation, but didnt find any usefull method. maybe
> i'm looking in the wrong place..
>
> thanks alot for your help,
> luigi
>
>
>
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