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I am dealing with a discrete math optimization problem on a complete graph. My variables are the arcs but I want to delete the arcs that "cost too much". I have $n$ nodes which means I have $n(n-1)$ arcs before deletion. I define the following set in AMPL

ARCS:={i in 1..n, j in 1..n : i!=j && d[i,j]<= R}

where d[i,j] is the cost on the arc (i,j) and R the limit I am putting.

My problem is that I don't know how to index the variables now. I know I can write

sum{ i in 1..n, j in 1..n : (i,j) in ARCS} blablabla[i,j]

But I think this is quite a tedious way to do. I thought I could write something like this sum{e in ARCS} blablabla[e[0],e[1]]

Thanks

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Try

sum{(i,j) in ARCS} blablabla[i,j]
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