Question: Problem with the differentiating a single value in a sum

Dear Mapleprimes,


I have a problem with the sum command. I'm differentiating wrt. a value q[i] in a sum. I have the following:


diff(sum((1/2)q[i], i=1..n),q[i]);


This returns:




but I'm differentiating wrt. q[i] not the whole sum. Any ideas?


Thanks very much.



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