[Scip] Regarding a MIP problem

[Tobias Achterberg]

Hi Gaurav,

I think it should be useful to remove the integrality restriction on the integer
objective variable. It will be integral anyway for every solution that is LP optimal
and integral for the binary variables.

Unfortunately, SCIP is not able to detect this implied integer property. Thus, it
might unnecessary branch on this variable or create cuts enforcing the integrality
and so on. I removed the integrality restriction, and the root node bound gets to 3
(the optimal value), which was not the case with the integrality restriction.

For this, you should disable strongcg cuts; they only seem to hurt performance:
separating/strongcg/freq = -1

cmir-cuts, however, seem to be slow but useful to find the 3 in the root node:
separating/cmir/freq = 0 (the default setting)


Tobias




gaurav khanna wrote:
> Hi all,
> 
> I have tried to use SCIP with MOSEK to solve a 0-1 MIP problem. The
> problem has 54061 variables and 78326 constraints. The instance has been
> running for the last 3 hours using the standard parameter file scip.set.
> To reduce the running time of the solver, is there any way I can change
> the parameter values in the scip.set file to speedup the  solution.
> Are there any specific parameters which I should target? Also,
> I am ok with getting feasible solutions to the MIP which need not be
> globally optimal. Is there a way to do that using SCIP that is to get a
> feasible solution in a lesser amount of time without significant loss in
> quality as compared to the global optimal.
> 
> The problem instance (MPS) is present at
> 
> http://www.cse.ohio-state.edu/~khannag/prob_8_lc.mps
> 
> Regards
> Gaurav
> 
> 
> Gaurav Khanna
> Phd Student
> CSE Department,OSU
> 
> Phone (office):614-292-7036
> 
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