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

[Sebastian Ruther]

  Hello Tobias,

yeah you were right. I stopped it after the root node and the statistics 
showed it took more than 3 hours to solve the LP. I guess I was 
expecting some kind of output as soon as the main solution process 
starts. That's why I assumed it was spending this much time to load the 
problem.

Cplex' barrier method solves the problem in 5 s. However I used it as a 
stand alone solver. When I call the barrier method in SCIP using
SCIP_CALL( SCIPsetCharParam(scip, "lp/initalgorithm", 'b') );
I get an assertion error:
lp->nlpicols == 0 && lp->nlpirows == 0, file [...]\src\scip\lp.c line 9244
what is going wrong?

Another question I have: I want to disable presolving. I use
SCIP_CALL( SCIPsetBoolParam(scip, "lp/presolving", FALSE) );
but presolving is executed nonetheless.  I load the default plug-ins
     SCIP_CALL( SCIPincludeDefaultPlugins(scip) );
and then call
     SCIP_CALL_ABORT(SCIPsolve(scip));

Thank you
Sebastian

On 16/08/2010 9:12 PM, Tobias Achterberg wrote:
> 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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> .
>