Documentation

Example Mip1.java

Example Mip1.java

This is the complete source code for our example (also available in <installdir>/examples/java/Mip1.java)...


/* Copyright 2019, Gurobi Optimization, LLC */

/* This example formulates and solves the following simple MIP model:

     maximize    x +   y + 2 z
     subject to  x + 2 y + 3 z <= 4
                 x +   y       >= 1
                 x, y, z binary
*/

import gurobi.*;

public class Mip1 {
  public static void main(String[] args) {
    try {

      // Create empty environment, set options, and start
      GRBEnv env = new GRBEnv(true);
      env.set("logFile", "mip1.log");
      env.start();

      // Create empty model
      GRBModel  model = new GRBModel(env);

      // Create variables
      GRBVar x = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "x");
      GRBVar y = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "y");
      GRBVar z = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "z");

      // Set objective: maximize x + y + 2 z
      GRBLinExpr expr = new GRBLinExpr();
      expr.addTerm(1.0, x); expr.addTerm(1.0, y); expr.addTerm(2.0, z);
      model.setObjective(expr, GRB.MAXIMIZE);

      // Add constraint: x + 2 y + 3 z <= 4
      expr = new GRBLinExpr();
      expr.addTerm(1.0, x); expr.addTerm(2.0, y); expr.addTerm(3.0, z);
      model.addConstr(expr, GRB.LESS_EQUAL, 4.0, "c0");

      // Add constraint: x + y >= 1
      expr = new GRBLinExpr();
      expr.addTerm(1.0, x); expr.addTerm(1.0, y);
      model.addConstr(expr, GRB.GREATER_EQUAL, 1.0, "c1");

      // Optimize model
      model.optimize();

      System.out.println(x.get(GRB.StringAttr.VarName)
                         + " " +x.get(GRB.DoubleAttr.X));
      System.out.println(y.get(GRB.StringAttr.VarName)
                         + " " +y.get(GRB.DoubleAttr.X));
      System.out.println(z.get(GRB.StringAttr.VarName)
                         + " " +z.get(GRB.DoubleAttr.X));

      System.out.println("Obj: " + model.get(GRB.DoubleAttr.ObjVal));

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

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