Searching for a particular kind of convergent sequence

  • Context: Graduate 
  • Thread starter Thread starter A-ManESL
  • Start date Start date
  • Tags Tags
    Convergent Sequence
Click For Summary

Discussion Overview

The discussion revolves around finding an example of a complex sequence that converges to 0 but does not belong to the space ℓ^p for any p ≥ 1, specifically focusing on the divergence of the series \(\sum |x_n|^p\).

Discussion Character

  • Exploratory, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant requests an example of a complex sequence (x_n) that converges to 0 but is not in ℓ^p for p ≥ 1.
  • Another participant suggests that the sequence \(x_n = \frac{1}{\log(n+1)}\) might work, although they have not verified the divergence for p > 1.
  • The same participant expresses confidence in their suggestion but encourages others to explore the necessary estimates for proving divergence without relying on obscure series tests.
  • A third participant indicates difficulty in establishing the divergence and asks for more explicit guidance.
  • A fourth participant proposes that for divergence, the inequality \((\frac{1}{\log(n)})^p > \frac{1}{n}\) holds for sufficiently large n.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the example of the sequence or the method for proving divergence, indicating ongoing exploration and differing viewpoints.

Contextual Notes

Some assumptions about the behavior of logarithmic functions and their implications for convergence and divergence are present but not fully explored or resolved.

Who May Find This Useful

Mathematicians and students interested in sequence convergence, functional analysis, and properties of ℓ^p spaces may find this discussion relevant.

A-ManESL
Messages
8
Reaction score
0
I want an example of a complex sequence (x_n) which converges to 0 but is not in ^p, for p\ge 1 i.e. the series \sum |x_n|^p is never convergent for any p\ge 1. Can someone provide an example please?
 
Physics news on Phys.org
I suspect 1/log(n+1) will work, but I haven't checked divergence for p > 1.

*EDIT* I'm fairly certain it works. I'll let you figure out the estimates needed to demonstrate divergence (hint: you don't need obscure series tests).
 
Last edited:
I am having trouble establishing the divergence. Can you be more explicit? Thanks.
 
For divergence I would guess (1/log(n))p > 1/n for sufficiently large n.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 17 ·
Replies
17
Views
6K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K