Hide navigation sidebar
Hide table of contents sidebar
Back to top
Toggle table of contents sidebar

# callback_cs.cs

    /* Copyright 2025, Gurobi Optimization, LLC */

    /*
       This example reads a model from a file, sets up a callback that
       monitors optimization progress and implements a custom
       termination strategy, and outputs progress information to the
       screen and to a log file.

       The termination strategy implemented in this callback stops the
       optimization of a MIP model once at least one of the following two
       conditions have been satisfied:
         1) The optimality gap is less than 10%
         2) At least 10000 nodes have been explored, and an integer feasible
            solution has been found.
       Note that termination is normally handled through Gurobi parameters
       (MIPGap, NodeLimit, etc.).  You should only use a callback for
       termination if the available parameters don't capture your desired
       termination criterion.
    */

    using System;
    using System.IO;
    using Gurobi;

    class callback_cs : GRBCallback
    {
      private double       lastiter;
      private double       lastnode;
      private GRBVar[]     vars;
      private StreamWriter logfile;

      public callback_cs(GRBVar[] xvars, StreamWriter xlogfile)
      {
        lastiter = lastnode = -GRB.INFINITY;
        vars = xvars;
        logfile = xlogfile;
      }

      protected override void Callback()
      {
        try {
          if (where == GRB.Callback.POLLING) {
            // Ignore polling callback
          } else if (where == GRB.Callback.PRESOLVE) {
            // Presolve callback
            int cdels = GetIntInfo(GRB.Callback.PRE_COLDEL);
            int rdels = GetIntInfo(GRB.Callback.PRE_ROWDEL);
            if (cdels != 0 || rdels != 0) {
              Console.WriteLine(cdels + " columns and " + rdels
                  + " rows are removed");
            }
          } else if (where == GRB.Callback.SIMPLEX) {
            // Simplex callback
            double itcnt = GetDoubleInfo(GRB.Callback.SPX_ITRCNT);
            if (itcnt - lastiter >= 100) {
              lastiter = itcnt;
              double obj    = GetDoubleInfo(GRB.Callback.SPX_OBJVAL);
              int    ispert = GetIntInfo(GRB.Callback.SPX_ISPERT);
              double pinf   = GetDoubleInfo(GRB.Callback.SPX_PRIMINF);
              double dinf   = GetDoubleInfo(GRB.Callback.SPX_DUALINF);
              char ch;
              if (ispert == 0)      ch = ' ';
              else if (ispert == 1) ch = 'S';
              else                  ch = 'P';
              Console.WriteLine(itcnt + " " + obj + ch + " "
                  + pinf + " " + dinf);
            }
          } else if (where == GRB.Callback.MIP) {
            // General MIP callback
            double nodecnt = GetDoubleInfo(GRB.Callback.MIP_NODCNT);
            double objbst  = GetDoubleInfo(GRB.Callback.MIP_OBJBST);
            double objbnd  = GetDoubleInfo(GRB.Callback.MIP_OBJBND);
            int    solcnt  = GetIntInfo(GRB.Callback.MIP_SOLCNT);
            if (nodecnt - lastnode >= 100) {
              lastnode = nodecnt;
              int actnodes = (int) GetDoubleInfo(GRB.Callback.MIP_NODLFT);
              int itcnt    = (int) GetDoubleInfo(GRB.Callback.MIP_ITRCNT);
              int cutcnt   = GetIntInfo(GRB.Callback.MIP_CUTCNT);
              Console.WriteLine(nodecnt + " " + actnodes + " "
                  + itcnt + " " + objbst + " " + objbnd + " "
                  + solcnt + " " + cutcnt);
            }
            if (Math.Abs(objbst - objbnd) < 0.1 * (1.0 + Math.Abs(objbst))) {
              Console.WriteLine("Stop early - 10% gap achieved");
              Abort();
            }
            if (nodecnt >= 10000 && solcnt > 0) {
              Console.WriteLine("Stop early - 10000 nodes explored");
              Abort();
            }
          } else if (where == GRB.Callback.MIPSOL) {
            // MIP solution callback
            int      nodecnt = (int) GetDoubleInfo(GRB.Callback.MIPSOL_NODCNT);
            double   obj     = GetDoubleInfo(GRB.Callback.MIPSOL_OBJ);
            int      solcnt  = GetIntInfo(GRB.Callback.MIPSOL_SOLCNT);
            double[] x       = GetSolution(vars);
            Console.WriteLine("**** New solution at node " + nodecnt
                + ", obj " + obj + ", sol " + solcnt
                + ", x[0] = " + x[0] + " ****");
          } else if (where == GRB.Callback.MIPNODE) {
            // MIP node callback
            Console.WriteLine("**** New node ****");
            if (GetIntInfo(GRB.Callback.MIPNODE_STATUS) == GRB.Status.OPTIMAL) {
              double[] x = GetNodeRel(vars);
              SetSolution(vars, x);
            }
          } else if (where == GRB.Callback.BARRIER) {
            // Barrier callback
            int    itcnt   = GetIntInfo(GRB.Callback.BARRIER_ITRCNT);
            double primobj = GetDoubleInfo(GRB.Callback.BARRIER_PRIMOBJ);
            double dualobj = GetDoubleInfo(GRB.Callback.BARRIER_DUALOBJ);
            double priminf = GetDoubleInfo(GRB.Callback.BARRIER_PRIMINF);
            double dualinf = GetDoubleInfo(GRB.Callback.BARRIER_DUALINF);
            double cmpl    = GetDoubleInfo(GRB.Callback.BARRIER_COMPL);
            Console.WriteLine(itcnt + " " + primobj + " " + dualobj + " "
                + priminf + " " + dualinf + " " + cmpl);
          } else if (where == GRB.Callback.MESSAGE) {
            // Message callback
            string msg = GetStringInfo(GRB.Callback.MSG_STRING);
            if (msg != null) logfile.Write(msg);
          }
        } catch (GRBException e) {
          Console.WriteLine("Error code: " + e.ErrorCode);
          Console.WriteLine(e.Message);
          Console.WriteLine(e.StackTrace);
        } catch (Exception e) {
          Console.WriteLine("Error during callback");
          Console.WriteLine(e.StackTrace);
        }
      }

      static void Main(string[] args)
      {
        if (args.Length < 1) {
          Console.Out.WriteLine("Usage: callback_cs filename");
          return;
        }

        StreamWriter logfile = null;

        try {
          // Create environment
          GRBEnv env = new GRBEnv();

          // Read model from file
          GRBModel model = new GRBModel(env, args[0]);

          // Turn off display and heuristics
          model.Parameters.OutputFlag = 0;
          model.Parameters.Heuristics = 0.0;

          // Open log file
          logfile = new StreamWriter("cb.log");

          // Create a callback object and associate it with the model
          GRBVar[]    vars = model.GetVars();
          callback_cs cb   = new callback_cs(vars, logfile);

          model.SetCallback(cb);

          // Solve model and capture solution information
          model.Optimize();

          Console.WriteLine("");
          Console.WriteLine("Optimization complete");
          if (model.SolCount == 0) {
            Console.WriteLine("No solution found, optimization status = "
                + model.Status);
          } else {
            Console.WriteLine("Solution found, objective = " + model.ObjVal);

            string[] vnames = model.Get(GRB.StringAttr.VarName, vars);
            double[] x      = model.Get(GRB.DoubleAttr.X, vars);

            for (int j = 0; j < vars.Length; j++) {
              if (x[j] != 0.0) Console.WriteLine(vnames[j] + " " + x[j]);
            }
          }

          // Dispose of model and environment
          model.Dispose();
          env.Dispose();

        } catch (GRBException e) {
          Console.WriteLine("Error code: " + e.ErrorCode);
          Console.WriteLine(e.Message);
          Console.WriteLine(e.StackTrace);
        } catch (Exception e) {
          Console.WriteLine("Error during optimization");
          Console.WriteLine(e.Message);
          Console.WriteLine(e.StackTrace);
        } finally {
          // Close log file
          if (logfile != null) logfile.Close();
        }
      }
    }

Help and Feedback

Press `/` or click to search this documentation | Gurobi website | Gurobi community forum
Go to other Gurobi documentation | Gurobi download | Contact support