Zulip Chat Archive

Stream: maths

Topic: Fubini for infinite series


Filippo A. E. Nuccio (Feb 02 2022 at 12:49):

Do we have Fubini's theorem for infinite series stating that we can exchange the order of doubly-indexed sequences under some absolute convergency assumption? We have docs#tsum_mul_tsum_of_summable_norm but this seems to apply only to "separable" series like

m=0n=0ambn\sum_{m=0}^{\infty}\sum_{n=0}^{\infty}a_m\cdot b_n

whereas I need it for abitrary double-indexed series like

m=0n=0cm,n=m,nN×Ncm,n\sum_{m=0}^{\infty}\sum_{n=0}^{\infty}c_{m,n}=\sum_{m,n \in \mathbb{N}\times\mathbb{N}}c_{m,n}

Heather Macbeth (Feb 02 2022 at 12:51):

Maybe docs#has_sum.prod_fiberwise applied twice?

Heather Macbeth (Feb 02 2022 at 12:53):

Or docs#tsum_comm'

Filippo A. E. Nuccio (Feb 02 2022 at 13:26):

Oh nice! Thank you.

Filippo A. E. Nuccio (Feb 02 2022 at 13:29):

I guess that what confuses me is that some of the results concerning series are in topology.algebra.infinite_sum and some are in normed_space.


Last updated: Dec 20 2023 at 11:08 UTC