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### feasopt_cs.cs

/* Copyright 2023, Gurobi Optimization, LLC */

/* This example reads a MIP model from a file, adds artificial
variables to each constraint, and then minimizes the sum of the
artificial variables.  A solution with objective zero corresponds
to a feasible solution to the input model.
We can also use FeasRelax feature to do it. In this example, we
use minrelax=1, i.e. optimizing the returned model finds a solution
that minimizes the original objective, but only from among those
solutions that minimize the sum of the artificial variables. */

using Gurobi;
using System;

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

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

// Create a copy to use FeasRelax feature later */
GRBModel feasmodel1 = new GRBModel(feasmodel);

// Clear objective
feasmodel.SetObjective(new GRBLinExpr());

GRBConstr[] c = feasmodel.GetConstrs();
for (int i = 0; i < c.Length; ++i) {
char sense = c[i].Sense;
if (sense != '>') {
GRBConstr[] constrs = new GRBConstr[] { c[i] };
double[] coeffs = new double[] { -1 };
coeffs, "ArtN_" + c[i].ConstrName);
}
if (sense != '<') {
GRBConstr[] constrs = new GRBConstr[] { c[i] };
double[] coeffs = new double[] { 1 };
coeffs, "ArtP_" +
c[i].ConstrName);
}
}

// Optimize modified model
feasmodel.Optimize();
feasmodel.Write("feasopt.lp");

// Use FeasRelax feature */
feasmodel1.FeasRelax(GRB.FEASRELAX_LINEAR, true, false, true);
feasmodel1.Write("feasopt1.lp");
feasmodel1.Optimize();

// Dispose of model and env
feasmodel1.Dispose();
feasmodel.Dispose();
env.Dispose();

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


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