Decision Optimization

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  • 1.  Cplex with C++

    Posted Wed January 26, 2022 10:30 AM

    Hi there,

    I am new to cplex and come across a question.

    Could you please show me how to solve this error?

    Thanks a lot!

    /* cplex code
       range C = 1..N;
       range Y = 1..10;
       range C_D = 1..(N+1);
       dvar int+ q[C_D][Y];
       int d[C] = ...; 
       dvar boolean y[C_D][C_D][Y]
       forall(j in C, m in Y)
         d[j]*sum(i in C_D) y[i][j][m] <= q[j][m];
    //I translate this constraint to C++ as following:
        for (int j = 0; j < C; ++j)
            for (int m = 0; m < Y; ++m) {
                IloExpr expr {env};
                for (int i = 0; i < V; ++i)
                    if (y[i][j][m] <= q[j][m]) // error: Cannot convert "IloConstraint" to bool       
                        expr += (y[i][j][m] <= q[j][m]);
                model.add(d[j] * expr);

    Shouwei Li

  • 2.  RE: Cplex with C++
    Best Answer

    Posted Thu January 27, 2022 04:29 AM
    Dear Shouwei,

    The expression :

    y[i][j][m] <= q[j][m]​

    cannot be used in an if statement since it is of type IloConstraint. The reason for that is that y[i][j][m] is a model object for which the  <= operator has been overloaded, and so returns an IloConstraint.
    You shouldn't declare y (nor q) as to contain model objects but as plain C++ 3d  (or 2d for q) matrices.
    I hope this helps,

    Renaud Dumeur

  • 3.  RE: Cplex with C++

    Posted Thu January 27, 2022 02:40 PM
    Hi Renaud,
    Thanks for your reply.
    It's clear to me now.

    Shouwei Li