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Re: symbolic and indefinite differentiation


> expr = Sum[a[k]*x^k, {k, 1, p}];
> D[expr, x] /. HoldPattern[Sum[a_, b__]] :> Sum[Evaluate[a], b]
>
> ???

I think that what he's trying to do is rather something like

p = 100;
Array[x, p];
f = Sum[x[i]^2, {i, 1, p}];
j = 43;
D[f, x[j]]

but leaving p and j undefined.




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