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### gc_funcnonlinear_cs.cs

/* Copyright 2024, Gurobi Optimization, LLC

This example considers the following nonconvex nonlinear problem

minimize   sin(x) + cos(2*x) + 1
subject to  0.25*exp(x) - x <= 0
-1 <= x <= 4

We show you two approaches to solve it as a nonlinear model:

1) Set the paramter FuncNonlinear = 1 to handle all general function
constraints as true nonlinear functions.

2) Set the attribute FuncNonlinear = 1 for each general function
constraint to handle these as true nonlinear functions.
*/

using System;
using Gurobi;

class gc_funcnonlinear_cs {

private static void printsol(GRBModel m, GRBVar x) {
Console.WriteLine("x = " + x.X);
Console.WriteLine("Obj = " + m.ObjVal);
}

static void Main() {
try {

// Create environment

GRBEnv env = new GRBEnv();

// Create a new model

GRBModel m = new GRBModel(env);

GRBVar x     = m.AddVar(-1.0, 4.0, 0.0, GRB.CONTINUOUS, "x");
GRBVar twox  = m.AddVar(-2.0, 8.0, 0.0, GRB.CONTINUOUS, "twox");
GRBVar sinx  = m.AddVar(-1.0, 1.0, 0.0, GRB.CONTINUOUS, "sinx");
GRBVar cos2x = m.AddVar(-1.0, 1.0, 0.0, GRB.CONTINUOUS, "cos2x");
GRBVar expx  = m.AddVar(0.0, GRB.INFINITY, 0.0, GRB.CONTINUOUS, "expx");

// Set objective

m.SetObjective(sinx + cos2x + 1, GRB.MINIMIZE);

m.AddConstr(0.25*expx - x <= 0, "l1");
m.AddConstr(2*x - twox == 0, "l2");

// sinx = sin(x)
GRBGenConstr gcf1 = m.AddGenConstrSin(x, sinx, "gcf1", "");
// cos2x = cos(twox)
GRBGenConstr gcf2 = m.AddGenConstrCos(twox, cos2x, "gcf2", "");
// expx = exp(x)
GRBGenConstr gcf3 = m.AddGenConstrExp(x, expx, "gcf3", "");

// Approach 1) Set FuncNonlinear parameter

m.Parameters.FuncNonlinear = 1;

// Optimize the model and print solution

m.Optimize();
printsol(m, x);

// Restore unsolved state and set parameter Funcnonlinear to its
// default value
m.Reset();
m.Parameters.FuncNonlinear = 0;

// Approach 2) Set FuncNonlinear attribute for every
//             general function constraint

gcf1.Set(GRB.IntAttr.FuncNonlinear, 1);
gcf2.Set(GRB.IntAttr.FuncNonlinear, 1);
gcf3.Set(GRB.IntAttr.FuncNonlinear, 1);

// Optimize the model and print solution

m.Optimize();
printsol(m, x);

// Dispose of model and environment

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


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