lp_c++.cpp

/* Copyright 2024, Gurobi Optimization, LLC */

/* This example reads an LP model from a file and solves it.
   If the model is infeasible or unbounded, the example turns off
   presolve and solves the model again. If the model is infeasible,
   the example computes an Irreducible Inconsistent Subsystem (IIS),
   and writes it to a file */

#include "gurobi_c++.h"
using namespace std;

int
main(int   argc,
     char *argv[])
{
  if (argc < 2) {
    cout << "Usage: lp_c++ filename" << endl;
    return 1;
  }

  try {
    GRBEnv env = GRBEnv();
    GRBModel model = GRBModel(env, argv[1]);

    model.optimize();

    int optimstatus = model.get(GRB_IntAttr_Status);

    if (optimstatus == GRB_INF_OR_UNBD) {
      model.set(GRB_IntParam_Presolve, 0);
      model.optimize();
      optimstatus = model.get(GRB_IntAttr_Status);
    }

    if (optimstatus == GRB_OPTIMAL) {
      double objval = model.get(GRB_DoubleAttr_ObjVal);
      cout << "Optimal objective: " << objval << endl;
    } else if (optimstatus == GRB_INFEASIBLE) {
      cout << "Model is infeasible" << endl;

      // compute and write out IIS

      model.computeIIS();
      model.write("model.ilp");
    } else if (optimstatus == GRB_UNBOUNDED) {
      cout << "Model is unbounded" << endl;
    } else {
      cout << "Optimization was stopped with status = "
           << optimstatus << endl;
    }

  } catch(GRBException e) {
    cout << "Error code = " << e.getErrorCode() << endl;
    cout << e.getMessage() << endl;
  } catch (...) {
    cout << "Error during optimization" << endl;
  }

  return 0;
}