Cannot set objective function in Gurobi model C++

Answered

Giorgos Tsoumos

March 04, 2023 09:21

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Hello,

I have tried to set the objective function in my model based on a quadatric expression GRBQuadExpr that i return from a function in different file other than Main.cpp. But when i run the program it terminates with error 20001 "Variable not in model". 

//test.cpp

typedef std::vector<std::pair<float, float>> vec_pair;

namespace PDPTW_Init

{

int vehicles,customers;

vehicles = 10;
customers = 101;

// This is the initialization of d_matrix
GRB_vec2d init_d_matrix(GRBModel& model,vec_pair coords)
    {
        GRB_vec2d c_matrix(customers, std::vector<GRBVar>(customers));

        for (int i = 0; i < customers; i++)
        {
            c_matrix[i][i] = model.addVar(0, GRB_INFINITY, 0, GRB_CONTINUOUS, "dist from x " + std::to_string(i) + " to " + std::to_string(i)); // Distance from self is zero
            for (int j = 0; j < customers && j!=i; j++)
            {

                double dist_i_j = sqrt(pow((coords[i].first - coords[j].first), 2) + pow((coords[i].second - coords[j].second), 2));

                c_matrix[i][j] = model.addVar(0, GRB_INFINITY,
                    dist_i_j, GRB_CONTINUOUS,
                    "dist from x " + std::to_string(i) + " to " + std::to_string(j));
            }
        }

        return c_matrix;
    }

GRBQuadExpr get_objective(std::vector<std::vector<GRBVar>> c_matrix, GRBVar*** x)
    {
        GRBQuadExpr obj = 0.0;

        for (int k = 0; k < vehicles; k++)
        {
            for (int i = 0; i < customers; i++)
            {
                for (int j = 0; j < customers; j++)
                {
                    
                    obj += c_matrix[i][j] * x[i][j][k];
                }
            }
        }
        return obj;
    }
}

// main.cpp

int main(int argc, char* argv[])
{
        GRBEnv env = GRBEnv();
        GRBModel model = GRBModel(env);

        obj = PDPTW_Init::get_objective(d_matrix, x);

        model.setObjective(obj,GRB_MINIMIZE); // Here is the error
}

 

Thanks in advance.

Related to

• Formulation
• C++
• Error

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 13, 2026 01:47

  This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  Jaromił Najman

  • Gurobi Staff

  March 07, 2023 08:50

  Hi Giorgos,

  In your code snippet, I cannot find a call to \(\texttt{init_d_matrix}\), which would initialize the matrix entries and create the \(\texttt{x}\) variables.

  Best regards, 
  Jaromił

  0

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