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());
// Add slack variables
GRBConstr[] c = feasmodel.GetConstrs();
for (int i = 0; i < c.Length; ++i)
{
char sense = c[i].Get(GRB.CharAttr.Sense);
if (sense != '>')
{
GRBConstr[] constrs = new GRBConstr[] { c[i] };
double[] coeffs = new double[] { -1 };
feasmodel.AddVar(0.0, GRB.INFINITY, 1.0, GRB.CONTINUOUS, constrs,
coeffs, "ArtN_" + c[i].Get(GRB.StringAttr.ConstrName));
}
if (sense != '<')
{
GRBConstr[] constrs = new GRBConstr[] { c[i] };
double[] coeffs = new double[] { 1 };
feasmodel.AddVar(0.0, GRB.INFINITY, 1.0, GRB.CONTINUOUS, constrs,
coeffs, "ArtP_" +
c[i].Get(GRB.StringAttr.ConstrName));
}
}
feasmodel.Update();
// Optimize modified model
feasmodel.Write("feasopt.lp");
feasmodel.Optimize();
// 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);
}
}
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());
// Add slack variables
GRBConstr[] c = feasmodel.GetConstrs();
for (int i = 0; i < c.Length; ++i) {
char sense = c[i].Get(GRB.CharAttr.Sense);
if (sense != '>') {
GRBConstr[] constrs = new GRBConstr[] { c[i] };
double[] coeffs = new double[] { -1 };
feasmodel.AddVar(0.0, GRB.INFINITY, 1.0, GRB.CONTINUOUS, constrs,
coeffs, "ArtN_" + c[i].Get(GRB.StringAttr.ConstrName));
}
if (sense != '<') {
GRBConstr[] constrs = new GRBConstr[] { c[i] };
double[] coeffs = new double[] { 1 };
feasmodel.AddVar(0.0, GRB.INFINITY, 1.0, GRB.CONTINUOUS, constrs,
coeffs, "ArtP_" +
c[i].Get(GRB.StringAttr.ConstrName));
}
}
feasmodel.Update();
// Optimize modified model
feasmodel.Write("feasopt.lp");
feasmodel.Optimize();
// 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);
}
}
static void Main()
{
try {
// Sample data
// Sets of days and workers
string[] Shifts =
new string[] { "Mon1", "Tue2", "Wed3", "Thu4", "Fri5", "Sat6",
"Sun7", "Mon8", "Tue9", "Wed10", "Thu11", "Fri12", "Sat13",
"Sun14" };
string[] Workers =
new string[] { "Amy", "Bob", "Cathy", "Dan", "Ed", "Fred", "Gu" };
int nShifts = Shifts.Length;
int nWorkers = Workers.Length;
// Number of workers required for each shift
double[] shiftRequirements =
new double[] { 3, 2, 4, 4, 5, 6, 5, 2, 2, 3, 4, 6, 7, 5 };
// Amount each worker is paid to work one shift
double[] pay = new double[] { 10, 12, 10, 8, 8, 9, 11 };
// Worker availability: 0 if the worker is unavailable for a shift
double[,] availability =
new double[, ] {
{ 0, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1 },
{ 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0 },
{ 0, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1 },
{ 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1 },
{ 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1 },
{ 1, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1 },
{ 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 }
};
// Model
GRBEnv env = new GRBEnv();
GRBModel model = new GRBModel(env);
model.ModelName = "assignment";
// Assignment variables: x[w][s] == 1 if worker w is assigned
// to shift s. Since an assignment model always produces integer
// solutions, we use continuous variables and solve as an LP.
GRBVar[,] x = new GRBVar[nWorkers, nShifts];
for (int w = 0; w < nWorkers; ++w)
{
for (int s = 0; s < nShifts; ++s)
{
x[w, s] =
model.AddVar(0, availability[w, s], pay[w], GRB.CONTINUOUS,
Workers[w] + "." + Shifts[s]);
}
}
// The objective is to minimize the total pay costs
model.ModelSense = GRB.MINIMIZE;
// Constraint: assign exactly shiftRequirements[s] workers
// to each shift s
for (int s = 0; s < nShifts; ++s)
{
GRBLinExpr lhs = 0.0;
for (int w = 0; w < nWorkers; ++w)
{
lhs.AddTerm(1.0, x[w, s]);
}
model.AddConstr(lhs == shiftRequirements[s], Shifts[s]);
}
// Optimize
model.Optimize();
int status = model.Status;
if (status == GRB.Status.UNBOUNDED)
{
Console.WriteLine("The model cannot be solved "
+ "because it is unbounded");
return;
}
if (status == GRB.Status.OPTIMAL)
{
Console.WriteLine("The optimal objective is " + model.ObjVal);
return;
}
if ((status != GRB.Status.INF_OR_UNBD) &&
(status != GRB.Status.INFEASIBLE))
{
Console.WriteLine("Optimization was stopped with status " + status);
return;
}
// Relax the constraints to make the model feasible
Console.WriteLine("The model is infeasible; relaxing the constraints");
int orignumvars = model.NumVars;
model.FeasRelax(0, false, false, true);
model.Optimize();
status = model.Status;
if ((status == GRB.Status.INF_OR_UNBD) ||
(status == GRB.Status.INFEASIBLE) ||
(status == GRB.Status.UNBOUNDED))
{
Console.WriteLine("The relaxed model cannot be solved "
+ "because it is infeasible or unbounded");
return;
}
if (status != GRB.Status.OPTIMAL)
{
Console.WriteLine("Optimization was stopped with status " + status);
return;
}
Console.WriteLine("\nSlack values:");
GRBVar[] vars = model.GetVars();
for (int i = orignumvars; i < model.NumVars; ++i)
{
GRBVar sv = vars[i];
if (sv.X > 1e-6)
{
Console.WriteLine(sv.VarName + " = " + sv.X);
}
}
// Dispose of model and environment
model.Dispose();
env.Dispose();
} catch (GRBException e) {
Console.WriteLine("Error code: " + e.ErrorCode + ". " +
e.Message);
}
}
