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### qp_cs.cs

/* Copyright 2020, Gurobi Optimization, LLC */

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

minimize    x^2 + x*y + y^2 + y*z + z^2 + 2 x
subject to  x + 2 y + 3 z >= 4
x +   y       >= 1
x, y, z non-negative

It solves it once as a continuous model, and once as an integer model.
*/

using System;
using Gurobi;

class qp_cs
{
static void Main()
{
try {
GRBEnv    env   = new GRBEnv("qp.log");
GRBModel  model = new GRBModel(env);

// Create variables

GRBVar x = model.AddVar(0.0, 1.0, 0.0, GRB.CONTINUOUS, "x");
GRBVar y = model.AddVar(0.0, 1.0, 0.0, GRB.CONTINUOUS, "y");
GRBVar z = model.AddVar(0.0, 1.0, 0.0, GRB.CONTINUOUS, "z");

// Set objective

GRBQuadExpr obj = x*x + x*y + y*y + y*z + z*z + 2*x;
model.SetObjective(obj);

// Add constraint: x + 2 y + 3 z >= 4

model.AddConstr(x + 2 * y + 3 * z >= 4.0, "c0");

// Add constraint: x + y >= 1

model.AddConstr(x + y >= 1.0, "c1");

// Optimize model

model.Optimize();

Console.WriteLine(x.VarName + " " + x.X);
Console.WriteLine(y.VarName + " " + y.X);
Console.WriteLine(z.VarName + " " + z.X);

Console.WriteLine("Obj: " + model.ObjVal + " " + obj.Value);

// Change variable types to integer

x.VType = GRB.INTEGER;
y.VType = GRB.INTEGER;
z.VType = GRB.INTEGER;

// Optimize model

model.Optimize();

Console.WriteLine(x.VarName + " " + x.X);
Console.WriteLine(y.VarName + " " + y.X);
Console.WriteLine(z.VarName + " " + z.X);

Console.WriteLine("Obj: " + model.ObjVal + " " + obj.Value);

// Dispose of model and env

model.Dispose();
env.Dispose();

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