Sum Operator (Solver Foundation)
Evaluates an expression for each possible combination of values of some iterator variables, and returns the sum of the results.
Sum[iters…, expr]
Example
Sum[{p, Products}, x[p]]
Sum[{p, Products}, {s, Sources}, x[p, s]]
Sum[{i, 5}, x[i]]
Sum uses the same iterator forms as Foreach. If no iterators are specified, Sum just evaluates expr.