Originally posted by: Demétrios

Dear All,

I'm using the IBM ILOG CPLEX Optimization Studio V12.5 linux version. And I'm using Callable Library on C language. I'm trying to parallel my application using Threads. I'm following the steps described on this site:

http://web.njit.edu/all_topics/Prog_Lang_Docs/cplex80/doc/userman/html/moreUsing28.html#1006792

But, It's not working, i.e., the number of threads set in CPX_PARAM_THREADS is not running. I can follow the steps described on this site:

http://pic.dhe.ibm.com/infocenter/cosinfoc/v12r2/index.jsp?topic=%2Filog.odms.cplex.help%2FContent%2FOptimization%2FDocumentation%2FCPLEX%2F_pubskel%2FCPLEX934.html

If I use CPXsetintparam(env,CPX_PARAM_LPMETHOD, CPX_ALG_CONCURRENT) the parallelism works. But, in this case the CPLEX uses 3 different algorithms. And I need to parallelize just the primal simplex algorithm.

A piece of my code:


   env = CPXopenCPLEX (&status);

     if ( env == NULL ) {
      char  errmsg[CPXMESSAGEBUFSIZE];
      fprintf (stderr, "Could not open CPLEX environment.\n");
      CPXgeterrorstring (env, status, errmsg);
      fprintf (stderr, "%s", errmsg);
      goto TERMINATE;
   }

  status = CPXsetintparam (env, CPX_PARAM_SCRIND, CPX_OFF);
   if ( status ) {
      fprintf (stderr,
               "Failure to turn on screen indicator, error %d.\n", status);
      goto TERMINATE;
   }

   status = CPXsetintparam (env, CPX_PARAM_DATACHECK, CPX_ON);
   if ( status ) {
      fprintf (stderr,
               "Failure to turn on data checking, error %d.\n", status);
      goto TERMINATE;
   }

   lp = CPXcreateprob (env, &status, "lpex1");

   if ( lp == NULL ) {
      fprintf (stderr, "Failed to create LP.\n");
      goto TERMINATE;
   }

   status = CPXsetintparam (env, CPX_PARAM_THREADS, 12);
   if ( status ) {
      fprintf (stderr,
               "Failure to set the number of threads, error %d.\n", status);
      goto TERMINATE;
   }
   
   status = CPXsetintparam (env, CPX_PARAM_PARALLELMODE, CPX_PARALLEL_DETERMINISTIC);
   if ( status ) {
      fprintf (stderr,
               "Failure to set the parallel mode, error %d.\n", status);
      goto TERMINATE;
   }
   
   status = populatebynonzero (env, lp,argc,argv);

   if ( status ) {
      fprintf (stderr, "Failed to populate problem.\n");
      goto TERMINATE;
   }

   status = CPXsetintparam (env, CPX_PARAM_ITLIM, 5000);
   
   if ( status ) {
      fprintf (stderr,
               "Failed to set the optimization method, error %d.\n", status);
      goto TERMINATE;
   }   
   
   status = CPXprimopt(env, lp);
   if ( status ) {
      fprintf (stderr, "Failed to optimize LP.\n");
      goto TERMINATE;
   }

   status =  CPXgetobjval (env, lp,&objval);
   if ( status ) {
      fprintf (stderr, "Failed to obtain solution.\n");
      goto TERMINATE;
   }
   
   so, What am I doing wrong?

There is no parallelization for the primal simplex algorithm in CPLEX. This is due to the nature of the algorithm itself.

If you only run primal simplex then you will gain nothing by using more than one thread.