Originally posted by: Hareg

Hello

I am using CPLEX to solve a complex MILP problem. I am getting optimal results for small sized input. And I want to test the limit of the system for a small sized problem. The problem has one parameter representing the number of flows in a network.  My problem is that, after some steps when I increase the number of flows by one,  the run time of CPLEX goes from just 11second to almost infinity. 

The engine log is not displaying anything, so I am having difficulty figuring out the source of the problem. Can anyone please help in shading light for me?

Thanks in advance!

Do I understand correctly that there is no log output and CPLEX seems stuck? If so, can you try setting CPX_PARAM_MIPDISPLAY to 4 and see if that gives more output? Can you please attach here the engine output for the instance that takes 11 seconds and the one that takes infinite time?
 

Originally posted by: Hareg

Hello 

Thank you very much for your fast response!

I have attached the engine outputs. I have changed the setting CPX_PARAM_MIPDISPLAY to 4 but still there is no change. The CPLEX seem to be stuck. I would really appreciate it if you have any suggestion as to why this might be.

Thank you!

Originally posted by: BoJensen

If the CPX_PARAM_MIPDISPLAY is set, then you should see some logging in the engine tab. Could you please try to write out the problem and load it into the interactive commandline prompt and paste the log. If possible please send the two problems to bo.jensen at dk dot ibm dot com. Also make sure you use the most recent release.

Originally posted by: Hareg

One more thing, CPLEX is reading the data from Microsoft access 2016. I was wandering, is there a limit on the number of records that CPLEX can read from a table? 

Originally posted by: Fatma Ahmed

when I am using it to solve a small scale problem, it solve it within 27 seconds but when I activate the display option "on" it takes 5 hours to obtain the same results. so Is there any explanation why this happen?

Do when we use options it may change the default settings which may increase the time of computation?

You only changed display from off to on? I have a hard time believing that this would change anything in the solution time. Can you show the two variants of your code?

Originally posted by: Fatma Ahmed

Thanks for your prompt reply.

I only added the yellow highlighted

ctype = GetCtype(N);

   options = cplexoptimset;

   options.Display = 'on';

sssss = size(ub,1);

tic

 [x, fval, exitflag, output] = cplexmilp (f, Aineq, bineq, Aeq, beq,...

      [ ], [ ], [ ], lb, ub, ctype, zeros(sssss),options);

What if you pass [] instead of zeros(sssss) for the x0 parameter (i.e., no starting point)?