Lp Examples#

This section includes source code for all of the Gurobi lp examples. The same source code can be found in the examples directory of the Gurobi distribution.

/* 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 <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "gurobi_c.h"

int
main(int   argc,
     char *argv[])
{
  GRBenv   *env   = NULL;
  GRBmodel *model = NULL;
  int       error = 0;
  int       optimstatus;
  double    objval;

  if (argc < 2) {
    fprintf(stderr, "Usage: lp_c filename\n");
    exit(1);
  }

  /* Create environment */

  error = GRBloadenv(&env, "lp.log");
  if (error) goto QUIT;

  /* Read model from file */

  error = GRBreadmodel(env, argv[1], &model);
  if (error) goto QUIT;

  /* Solve model */

  error = GRBoptimize(model);
  if (error) goto QUIT;

  /* Capture solution information */

  error = GRBgetintattr(model, GRB_INT_ATTR_STATUS, &optimstatus);
  if (error) goto QUIT;

  /* If model is infeasible or unbounded, turn off presolve and resolve */

  if (optimstatus == GRB_INF_OR_UNBD) {
    /* Change parameter on model environment.  The model now has
       a copy of the original environment, so changing the original will
       no longer affect the model.  */

    error = GRBsetintparam(GRBgetenv(model), "PRESOLVE", 0);
    if (error) goto QUIT;

    error = GRBoptimize(model);
    if (error) goto QUIT;

    error = GRBgetintattr(model, GRB_INT_ATTR_STATUS, &optimstatus);
    if (error) goto QUIT;
  }

  if (optimstatus == GRB_OPTIMAL) {
    error = GRBgetdblattr(model, GRB_DBL_ATTR_OBJVAL, &objval);
    if (error) goto QUIT;
    printf("Optimal objective: %.4e\n\n", objval);
  } else if (optimstatus == GRB_INFEASIBLE) {
    printf("Model is infeasible\n\n");

    error = GRBcomputeIIS(model);
    if (error) goto QUIT;

    error = GRBwrite(model, "model.ilp");
    if (error) goto QUIT;
  } else if (optimstatus == GRB_UNBOUNDED) {
    printf("Model is unbounded\n\n");
  } else {
    printf("Optimization was stopped with status = %d\n\n", optimstatus);
  }

QUIT:

  /* Error reporting */

  if (error) {
    printf("ERROR: %s\n", GRBgeterrormsg(env));
    exit(1);
  }

  /* Free model */

  GRBfreemodel(model);

  /* Free environment */

  GRBfreeenv(env);

  return 0;
}

/* 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;
}

/* 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. */

using System;
using Gurobi;

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

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

      model.Optimize();

      int optimstatus = model.Status;

      if (optimstatus == GRB.Status.INF_OR_UNBD) {
        model.Parameters.Presolve = 0;
        model.Optimize();
        optimstatus = model.Status;
      }

      if (optimstatus == GRB.Status.OPTIMAL) {
        double objval = model.ObjVal;
        Console.WriteLine("Optimal objective: " + objval);
      } else if (optimstatus == GRB.Status.INFEASIBLE) {
        Console.WriteLine("Model is infeasible");

        // compute and write out IIS

        model.ComputeIIS();
        model.Write("model.ilp");
      } else if (optimstatus == GRB.Status.UNBOUNDED) {
        Console.WriteLine("Model is unbounded");
      } else {
        Console.WriteLine("Optimization was stopped with status = "
                           + optimstatus);
      }

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

    } catch (GRBException e) {
      Console.WriteLine("Error code: " + e.ErrorCode + ". " + e.Message);
    }
  }
}

/* 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());
    }
  }
}

function lp()
% Copyright 2024, Gurobi Optimization, LLC
%
% This example formulates and solves the following simple LP model:
% maximize
%       x + 2 y + 3 z
% subject to
%       x +   y        <= 1
%             y +   z  <= 1
%

model.A = sparse([1 1 0; 0 1 1]);
model.obj = [1 2 3];
model.modelsense = 'Max';
model.rhs = [1 1];
model.sense = [ '<' '<'];

result = gurobi(model);

disp(result.objval);
disp(result.x);

% Alterantive representation of A - as sparse triplet matrix
i = [1; 1; 2; 2];
j = [1; 2; 2; 3];
x = [1; 1; 1; 1];
model.A = sparse(i, j, x, 2, 3);

% Set some parameters
params.method = 2;
params.timelimit = 100;

result = gurobi(model, params);

disp(result.objval);
disp(result.x)
end

#!/usr/bin/env python3.11

# 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 sys
import gurobipy as gp
from gurobipy import GRB

if len(sys.argv) < 2:
    print("Usage: lp.py filename")
    sys.exit(0)

# Read and solve model

model = gp.read(sys.argv[1])
model.optimize()

if model.Status == GRB.INF_OR_UNBD:
    # Turn presolve off to determine whether model is infeasible
    # or unbounded
    model.setParam(GRB.Param.Presolve, 0)
    model.optimize()

if model.Status == GRB.OPTIMAL:
    print(f"Optimal objective: {model.ObjVal:g}")
    model.write("model.sol")
    sys.exit(0)
elif model.Status != GRB.INFEASIBLE:
    print(f"Optimization was stopped with status {model.Status}")
    sys.exit(0)


# Model is infeasible - compute an Irreducible Inconsistent Subsystem (IIS)

print("")
print("Model is infeasible")
model.computeIIS()
model.write("model.ilp")
print("IIS written to file 'model.ilp'")

# Copyright 2024, Gurobi Optimization, LLC
#
# This example formulates and solves the following simple LP model:
#  maximize
#        x + 2 y + 3 z
#  subject to
#        x +   y       <= 1
#              y +   z <= 1

library(Matrix)
library(gurobi)

model <- list()

model$A          <- matrix(c(1,1,0,0,1,1), nrow=2, byrow=T)
model$obj        <- c(1,2,3)
model$modelsense <- 'max'
model$rhs        <- c(1,1)
model$sense      <- c('<', '<')

result <- gurobi(model)

print(result$objval)
print(result$x)

# Second option for A - as a sparseMatrix (using the Matrix package)...

model$A <- spMatrix(2, 3, c(1, 1, 2, 2), c(1, 2, 2, 3), c(1, 1, 1, 1))

params <- list(Method=2, TimeLimit=100)

result <- gurobi(model, params)

print(result$objval)
print(result$x)

# Third option for A - as a sparse triplet matrix (using the slam package)...

model$A <- simple_triplet_matrix(c(1, 1, 2, 2), c(1, 2, 2, 3), c(1, 1, 1, 1))

params <- list(Method=2, TimeLimit=100)

result <- gurobi(model, params)

print(result$objval)
print(result$x)

# Clear space
rm(result, params, model)

' 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.

Imports System
Imports Gurobi

Class lp_vb
    Shared Sub Main(ByVal args As String())

        If args.Length < 1 Then
            Console.WriteLine("Usage: lp_vb filename")
            Return
        End If

        Try
            Dim env As GRBEnv = New GRBEnv("lp1.log")
            Dim model As GRBModel = New GRBModel(env, args(0))

            model.Optimize()

            Dim optimstatus As Integer = model.Status

            If optimstatus = GRB.Status.INF_OR_UNBD Then
                model.Parameters.Presolve = 0
                model.Optimize()
                optimstatus = model.Status
            End If

            If optimstatus = GRB.Status.OPTIMAL Then
                Dim objval As Double = model.ObjVal
                Console.WriteLine("Optimal objective: " & objval)
            ElseIf optimstatus = GRB.Status.INFEASIBLE Then
                Console.WriteLine("Model is infeasible")
                model.ComputeIIS()
                model.Write("model.ilp")
            ElseIf optimstatus = GRB.Status.UNBOUNDED Then
                Console.WriteLine("Model is unbounded")
            Else
                Console.WriteLine("Optimization was stopped with status = " & _
                                  optimstatus)
            End If

            ' Dispose of model and env
            model.Dispose()
            env.Dispose()

        Catch e As GRBException
            Console.WriteLine("Error code: " & e.ErrorCode & ". " & e.Message)
        End Try
    End Sub
End Class

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