Possible bug in the symbolic differentiation of N unknown variables

[Snow Summer]

Hello, Sage Developers,

I want to calculate the symbolic differentiation of a variable in an expression with a sum of N unknown variables, and it seems sage cannot handle it. I posted my question in https://ask.sagemath.org/question/62451/how-to-symbolic-differentiate-a-sum-of-n-unknown-variables/ , and the answer says it is a bug in sage. How can I report a bug? Is this bug already reported somewhere?

Thanks,

[Nils Bruin]

The bug is perhaps concisely illustrated with the following:

sage: var('k,n')
(k, n)
sage: function('f')
f
sage: sum(f(x,k),k,1,n).diff(x)
diff(f(x, k), x)*D[0](sum)(f(x, k), k, 1, n)

it shows that  sage doesn't have a  differentiation rule in place for symbolic sums and just applies the chain rule on the first argument (and undoubtedly on the others, but those are constants in x). I would expect that there is a ticket lying around about this (some care needs to be taken to do something sensible with the other arguments as well), but I wasn't able to locate one.

[Nils Bruin]

Actually, this case is fully covered by

https://trac.sagemath.org/ticket/32161

which is, unfortunately, stalled on what looks like a non-trivial problem with a more general solution. Given that the problem arises again here, perhaps it's worth accepting first a more limited solution and just stick with errors on non-constant summation bounds.

[Snow Summer]

Thanks!

[Emmanuel Charpentier]

As I understand it, differentiating a discrete sum with respect to its bounds is nonsense ; see my comment in the ticket.

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