Calculate a Double Sum

Calculator for double sums, the connections of two sums, an inner and an outer sum. The inner sum with the running variable j runs from o to p, the outer sum with the running variable i from m to n. Only the variables i and j may occur in the sum term. The basic arithmetic operations + - * / are allowed, as well as the power function, like pow(j#i) for jⁱ. Further allowed functions are sin(), cos(), tan(), asin(), acos(), atan(), log() for the natural logarithm and fac() for the factorial. Also, the constants e and pi can be used. If i≠j is chosen, summands with equal running variables are omitted.