How can I calculate an intermediate sum of a subset of array elements to use in a downstream constraint in MiniZinc?

Question

I have an array a of type int [0,0,0,0,0] of length l

I want to calculate a sum of all elements with odd indexes to use in a downstream constraint, here some "pseudo" MiniZinc code:

s = sum(i in 1..l | i mod 2 == 0) (a[i]);

solve maximize(s);

How can this be done?

Answer 1

I don't know what a "downstream constraint" is, but you can use "where" to add a condition in the loop:

 constraint
     s = sum(i in 1..l where i mod 2 == 0) (a[i])
 ;