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Student Support Forum: 'Taking Derivative inside Sum' topicStudent Support Forum > General > Archives > "Taking Derivative inside Sum"

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J H Ettle
07/02/03 05:08am

I've been trying to take a derivative of a (general) summation (like the kind found in the attached notebook) with a symbolic upper limit. The derivative is with respect to a parameter that is passed to a function F inside the sum. I then multiply the summand by a function L of the index to get:

Sum[L[i] F[s], {i, 1, M}].

I then take the derivative of the above with respect to s. Mathematica passes the derivative into the sum, a-la

Sum[D[L[i] F[s], s], {i, 1, M}],

but doesn't carry the derivation on through. I have to manually extract the summand and evaluate it to get

L[i] F'[s],

as expected. Why is this? And how come Mathematica DOES carry the differentiation through when I try the same with an analogous integral?

Attachment: DerivativeAnomaly.nb, URL: ,

Subject (listing for 'Taking Derivative inside Sum')
Author Date Posted
Taking Derivative inside Sum J H Ettle 07/02/03 05:08am
Re: Taking Derivative inside Sum Forum Modera... 08/03/03 4:57pm
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