Lp.java

/* 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 */

import com.gurobi.gurobi.*;

public class Lp {
  public static void main(String[] args) {

    if (args.length < 1) {
      System.out.println("Usage: java Lp filename");
      System.exit(1);
    }

    try {
      GRBEnv env = new GRBEnv();
      GRBModel model = new GRBModel(env, args[0]);

      model.optimize();

      int optimstatus = model.get(GRB.IntAttr.Status);

      if (optimstatus == GRB.Status.INF_OR_UNBD) {
        model.set(GRB.IntParam.Presolve, 0);
        model.optimize();
        optimstatus = model.get(GRB.IntAttr.Status);
      }

      if (optimstatus == GRB.Status.OPTIMAL) {
        double objval = model.get(GRB.DoubleAttr.ObjVal);
        System.out.println("Optimal objective: " + objval);
      } else if (optimstatus == GRB.Status.INFEASIBLE) {
        System.out.println("Model is infeasible");

        // Compute and write out IIS
        model.computeIIS();
        model.write("model.ilp");
      } else if (optimstatus == GRB.Status.UNBOUNDED) {
        System.out.println("Model is unbounded");
      } else {
        System.out.println("Optimization was stopped with status = "
                           + optimstatus);
      }

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

    } catch (GRBException e) {
      System.out.println("Error code: " + e.getErrorCode() + ". " +
          e.getMessage());
    }
  }
}