Originally posted by: malithwd

Hi folks,

I am trying to model the following constrain in OPL. Here π G is string set.

        Np-1
r >= ∑ y(k,k+1)     ∀p∈ π G
        k=1       

Here is how I tried it,

tuple Path {{string} nodes;}
{Path} paths = ...;

subject to{

 forall(p in paths)
        sum (node in p.nodes) Y[node][next(p.nodes,node)]  <= r;

}

since i want to iterate till N-1 th element of set and apply function Y for k+1 th element i used "next" function. But here it iterates till N th element. How could it be done using OPL notation to iterate till N-1 th element and get the k+1 th element in function?

Thank you,

Malith

Originally posted by: OndrejKral

Hi, how about

 forall(p in paths)
        sum (node in p.nodes diff last(p.nodes)) Y[node][next(p.nodes,node)]  <= r;

}

Ondrej

Originally posted by: malithwd

Hi Ondrej,

Nice trick, Thanks. Just needed a little correction as follows (added curly braces to make it a set),

 forall(p in paths)
        sum (node in p.nodes diff {last(p.nodes)}) Y[node][next(p.nodes,node)]  <= r;

}

Cheers,

Malith