# Derivative of a sum with respect to the maximum step?

I am looking to take the derivative of $\partial _n(\sum_ {j=n/2}^{n} f(n,j))$ and I am not sure how to go about doing it. Can Anyone point Me in the direction of information about how to proceed? Thanks. [Note: While I did see the answer at What is the derivative of a summation with respect to it's upper limit?, I get the impression from the comments the answers given are wrong.]

-
As written, your function is defined only for integers $n$ (perhaps even only for even integers); in that context, derivatives make no sense. If you have in mind a function that is defined for all real numbers $n$, you should be specific about what you mean. – Greg Martin Mar 20 '13 at 2:55
@GregMartin: I'm not sure that's necessarily true. Consider the function $f(n,j) = nj$. The derivative of that function with respect to n is $f' = j$. – xuinkrbin. Mar 20 '13 at 3:38
True but irrelevant. What, for example, do you mean by $\sum_{j=\pi/2}^\pi f(\pi,j)$? – Greg Martin Mar 20 '13 at 6:25
You can find your answer Here: math.stackexchange.com/questions/248203/… – user99605 Oct 8 '13 at 14:40