Originally posted by: JDalal

Hi,

I am using CPLEX with C++ to model a facility location MIP problem. Suppose I := set of customer locations, J:= set of potential locations where facilities can open. Generally in textbook kind model, we use set I = set J and use IloNumVarArray to declare corresponding decision variables. For example, if I consider 50 locations, in x_ij both i and j indices are in {0,...49} or {1,...,50}

The issue is: unlike standard formulations, suppose I have the customer set I ={10,15,21} and J={4,5,8}. Then how to declare all x_ij variables like x_{10,4}, ..., x_{21,8} using for loop?
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Originally posted by: JDalal

I thought to better explain my question with a code snippet:

My working code is:

typedef IloArray<IloNumVarArray> IloNumVarArray2;
.
.
.
//declaring x_ij
IloNumVarArray2 x(env, num_of_customers);
for(int i=0;i<num_of_customers;i++){
x[i] = IloNumVarArray(env, num_of_location, 0, 1, ILOFLOAT);
}

This is simple, since the indices i and j are just {0,...,num_of_customers} and {0,...,num_of_location}.
Now I have the sets as some discrete integers like I={5,8,12} and j={2,21,49}.
What is a n effective way of coding in this situation?
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Originally posted by: SystemAdmin

In terms of your small example, why not just index customers 0..2 and locations 0..2? If the original indices (5, 8, 12 for customers; 2, 21, 49 for locations) have some significance elsewhere, you can store them in arrays (so that customer[0] = 5, location[0] = 2, etc.) for later use.

Paul

Mathematicians are like Frenchmen: whenever you say something to them, they translate it into their own language, and at once it is something entirely different. (Goethe)
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Originally posted by: JDalal

Thanks Paul.

I thought about the same way. I was just wandering if there is any better way of doing it in Concert technology, so that I can get rid of mapping those indices with corresponding values in another array. Something that AMPL offers to its user - any number, or may be string can be used as index of a variable. However, it is possibly also using the same mapping technique internally and hiding the details from end user.
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Originally posted by: SystemAdmin

I think it is not directly available in Concert. But it should be pretty easy to do that using either std::map<int,IloNumVar> or std::map<std::pair<int,int>,IloNumVar>.
Using these types would allow you to index variables by any number or pair of numbers.
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