Hello,

I am currently working on an LP formulation. During this process I create the following constraint, involving two objects r and s. Depending on their state they can either have a variable or a fixed value associated with their width:

IloNumVar variable_s_position, variable_r_position, variable_s_width, variable_r_width;
IloNumExpr distance = sum($variable_s_position, prod(-1, $variable_r_position));

if(r.isFlexible){
    if (s.isFlexible) {
        IloNumExpr lower_bound = sum($variable_width_s, $variable_width_r);
        add(ge(distance_below,lower_bound);
    } else {
        IloNumExpr lower_bound = sum(fixed_width_s, $variable_width_r);
        add(ge(distance_below,lower_bound);
    }
} else {
    if (s.isFlexible) {
        IloNumExpr lower_bound = sum($variable_width_s, fixed_width_r);
        add(ge(distance_below,lower_bound);
    } else {
        double lower_bounds = fixed_width_s + fixed_width_r;
        add(ge(distance_below,lower_bound);
    }
}

As you can see, I'm using the line "add(ge(distance_below,lower_bound);" 4 times, once in every branch. I realize that the fourth call is not the same function call as the second argument is a double variable instead of an IloNumExpr. I would like to refactor the code in something along the lines of the following example:

IloNumVar variable_s_position, variable_r_position, variable_s_width, variable_r_width;
IloNumExpr distance = sum($variable_s_position, prod(-1, $variable_r_position));
IloNumExpr lower_bound;

if(r.isFlexible){
    if (s.isFlexible) {
        lower_bound = sum($variable_width_s, $variable_width_r);
    } else {
        lower_bound = sum(fixed_width_s, $variable_width_r);
    }
} else {
    if (s.isFlexible) {
        lower_bound = sum($variable_width_s, fixed_width_r);
    } else {
        lower_bounds = fixed_width_s + fixed_width_r;
    }
}

add(ge(distance_below,lower_bound);

For the first three branches, this would work fine, but in the fourth branch, I would be assigning a double value to a IloNumExpr, which is not valid. Is there a way to save a constant value OR a an IloNumExpr in the same variable, such that this variable can be used as the right hand side of a constraint?

Comment: In the actual program, the case distinction might exceed 4 branches and need up to 64 calls to (almost) the same line.

------------------------------
Soeren Nickel
------------------------------

#DecisionOptimization

You did not specify which API you are using. If it is Java, you can invoke linearNumericExpr(lower_bound) on the IloCplex instance to get a linear numeric expression equal to lower_bound.

------------------------------
Paul Rubin
Professor Emeritus
Michigan State University
------------------------------

Thank you very much, I'm indeed using Java (I'll remember to specify that in future questions) and this solves my problem.

------------------------------
Soeren Nickel
------------------------------

Original Message:
Sent: Wed June 10, 2020 04:06 PM
From: Paul Rubin
Subject: Saving IloNumExpr or constant double value in the same variable

You did not specify which API you are using. If it is Java, you can invoke linearNumericExpr(lower_bound) on the IloCplex instance to get a linear numeric expression equal to lower_bound.

------------------------------
Paul Rubin
Professor Emeritus
Michigan State University
------------------------------