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

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SUMMARY

The series $$Y(x)= \sum_{n=1}^{\infty}(-1)^n\frac{x^n\ln^nx}{n!}$$ uniformly converges for all $x \in (0,1]$ due to the application of the M-test. The maximum value of $|x \ln x|$ is $\frac{1}{e}$, leading to the convergence of the series $$\sum_{n=0}^{\infty}\frac{(\frac{1}{e})^n}{n!}$$. Uniform convergence is established specifically on the interval $(0,1]$ and can be extended to any interval of the form $(0,a]$ for $a > 0$.

PREREQUISITES
  • Understanding of uniform convergence and pointwise convergence
  • Familiarity with the M-test for series convergence
  • Knowledge of logarithmic functions and their properties
  • Basic concepts of series and factorial notation
NEXT STEPS
  • Study the M-test in detail to understand its application in proving uniform convergence
  • Explore the properties of logarithmic functions, particularly in relation to convergence
  • Investigate uniform convergence on intervals beyond $(0,1]$
  • Learn about the implications of uniform convergence in integration of series
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Mathematicians, students studying real analysis, and anyone interested in series convergence and its applications in calculus.

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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