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

In summary, the given series $Y(x)$ uniformly converges for all $x\in(0,1]$ and this is proven by the M-test using the maximum of $|x\ln{x}|$. The series is only normally convergent on $(0,1]$, but for the given problem, uniform convergence is needed, so the proof must be extended to show uniform convergence on this interval.
  • #1
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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  • #2
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 $\max$?
 
  • #3
girdav said:
Where do you take the $\max$?

On positive $\mathbb{R}$ .
 
Last edited:
  • #4
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 $(0,1]$.
 
  • #5
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 ?
 
  • #6
You have the normal (hence uniform) convergence on each interval of the form $(0,a]$, $a>0$.
 

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

What is uniform convergence?

Uniform convergence is a type of convergence in which the convergence of a sequence of functions is independent of the value of x. In other words, the rate of convergence is the same for all points in the interval, thus the name "uniform". This is in contrast to pointwise convergence, where the rate of convergence can vary for different points in the interval.

What is the significance of uniform convergence?

Uniform convergence is important because it guarantees that the limit function is continuous. This is useful in many applications, such as in numerical analysis and in the study of differential equations.

How is uniform convergence different from pointwise convergence?

Pointwise convergence only requires that for each x in the interval, the sequence of functions converges to the limit function at that point. In contrast, uniform convergence requires that the rate of convergence is the same for all points in the interval.

What is the Cauchy criterion for uniform convergence?

The Cauchy criterion for uniform convergence states that a sequence of functions converges uniformly if and only if for any given epsilon greater than zero, there exists a natural number N such that for all n and m greater than N, the difference between the nth and mth functions is less than epsilon for all values of x in the interval.

How is uniform convergence related to continuity?

Uniform convergence implies continuity, meaning that if a sequence of functions converges uniformly, then the limit function is continuous. This is because the rate of convergence is the same for all points in the interval, so there are no sudden jumps or discontinuities in the limit function.

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