Uniform Convergence of $Y(x)$ in $(0,1]$

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Discussion Overview

The discussion revolves around the uniform convergence of the series $$Y(x)= \sum_{n=1}^{\infty}(-1)^n\frac{x^n\ln^nx}{n!}$$ for values of $x$ in the interval $(0,1]$. Participants explore the conditions under which this uniform convergence holds and seek clarification on the implications of their findings.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant asserts that $Y(x)$ is uniformly convergent on $(0,1]$ based on the M-test, citing the maximum value of $|x \ln x|$ as $\frac{1}{e}$.
  • Another participant questions the application of the maximum and emphasizes the need for clarity regarding uniform convergence as it pertains to a set rather than a single point.
  • A participant points out that if the maximum is taken over positive $\mathbb{R}$, it becomes infinite, suggesting that the series is normally convergent on $(0,1]$.
  • One participant expresses that normal convergence is insufficient for their needs, as they require uniform convergence to integrate the series.
  • A later reply indicates that uniform convergence is established on intervals of the form $(0,a]$ for any $a>0$.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the intervals of uniform convergence for $Y(x)$. While some agree on uniform convergence in $(0,1]$, others suggest it may hold on smaller intervals $(0,a]$ for $a>0$. The discussion remains unresolved regarding the broader implications of uniform convergence beyond these intervals.

Contextual Notes

There are limitations regarding the assumptions made about the maximum value and the implications of normal convergence versus uniform convergence. The discussion does not resolve these aspects fully.

Also sprach Zarathustra
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Hello!A little problem:With the given series,$$Y(x)= \sum_{n=1}^{\infty}(-1)^n\frac{x^n\ln^nx}{n!} $$ ,why $Y(x)$ is Uniformly converges for all $x\in(0,1]$ ?Ok, I know that $Y(x)$ is u.c by M-test:

$$\max{|x\ln{x}|}=\frac{1}{e}$$

And,

$$ \sum_{n=0}^{\infty}\frac{(\frac{1}{e})^n}{n!} $$

Is converges! But why only in $(0,1]$ ?
Thank you!
 
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We need some clarifications. First, we talk about uniform convergence on a set, not only at one point (in this case, it's pointwise convergence). Where do you take the $\max$?
 
girdav said:
Where do you take the $\max$?

On positive $\mathbb{R}$ .
 
Last edited:
In this case, the $\max$ is infinite. But if you take it on $(0,1]$, you will notice that the series is normally convergent on $(0,1]$.
 
girdav said:
In this case, the $\max$ is infinite. But if you take it on $(0,1]$, you will notice that the series is normally convergent on $(0,1]$.

Normally convergence is not enough for this problem that I have, I need integrate that sum,- I must first prove the U.C. on (0,1].

I'll rephrase my question: is that the only interval,(0,1], that Y(x) U.N in ?
 
You have the normal (hence uniform) convergence on each interval of the form $(0,a]$, $a>0$.
 

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