[Scip] SCIP doesn't start the solution process after presolving

[Tobias Achterberg]

Hi Sebastian,

my guess is that the root LP solve is just incredibly hard (or the LP solver has bad luck and struggles a lot with degeneration).

You can activate the LP solver output with the "display/lpinfo" parameter. This should give you a clue what happens. If it is the 
LP solve that takes so long, you may want to try the barrier algorithm (which is available by using CPLEX as LP solver, but not 
for Soplex): "lp/initalgorithm" = "b".


Tobias


Sebastian Ruther wrote:
>
>    Hello,
>
> I am trying to solve a MIP but SCIP or Cplex gets stuck somewhere.
> I load the default plug-ins and after presolving it doesn't start the
> main solution process
> .
> Presolving deletes 1300 variables and 800 constraints. After that the
> problem has 16000 constraints and 19600 variables with 19200 being
> binary and the rest continuous.
> After displaying the presolving time (which is 157 sec) nothing happens
> for at least one hour. The CPU is busy but like I said the main solution
> process is not started. What's going on? Is SCIP transferring the
> problem to Cplex? That shouldn't take so long for a medium seized problem.
> After 1-4 hours it starts the solution process.
>
> Regards,
> Sebastian
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