Does x^n f(x) Converge Uniformly on [0,1] as n Approaches Infinity?

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Discussion Overview

The discussion revolves around the uniform convergence of the function \( x^n f(x) \) on the interval \([0,1]\) as \( n \) approaches infinity, under the condition that \( f(x) \) is continuous on \([0,1]\) and \( f(1) = 0 \). The scope includes theoretical exploration and mathematical reasoning related to uniform convergence and continuity.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant proposes that by continuity, if \( |x-1|< \delta \), then \( |f(x)|< \epsilon \) for \( x \in [x_0 ,1] \) for some \( x_0 \in [0,1] \).
  • Another participant mentions that there exists some \( N \) such that if \( n>N \), then \( |x^n|<\epsilon \) since \( x^n \rightarrow 0 \) for \( x \in [0,1] \).
  • Concerns are raised about the applicability of uniform continuity on compact sets and its relevance to the question of uniform convergence.
  • One participant questions the necessity of certain statements regarding the continuity of \( f(x) \) and the implications for uniform convergence.
  • There is a request for clarification on the definition of uniform convergence, indicating a potential misunderstanding or need for further exploration of the concept.

Areas of Agreement / Disagreement

Participants express differing views on the implications of continuity and uniform convergence, with some questioning the reasoning presented and others affirming the continuity's role in establishing uniform convergence. The discussion remains unresolved with multiple competing views.

Contextual Notes

Participants highlight the importance of definitions related to uniform convergence and continuity, indicating potential limitations in the arguments presented. There is also an acknowledgment of the behavior of \( x^n \) at the endpoints of the interval.

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Suppose f(x) is continuous on [0,1], and that f(1)=0. Prove that [itex]x^n f(x)[/itex] converges uniformly on [0,1] as [itex]n \rightarrow \infty[/itex]

By continuity, if [itex]|x-1|< \delta[/itex] then [itex]|f(x)|< \epsilon[/itex] for [itex]x \in [x_0 ,1][/itex] for some [itex]x_0 \in [0,1][/itex].

And there is some N such that if n>N, then [itex]|x^n|<\epsilon[/itex] since [itex]x^n \rightarrow 0[/itex] for [itex]x \in [0,1][/itex].

The endpoints work since x^nf(x) is 0 there. So I have an N that works for [itex]\{ 0 \} \cup [x_0, 1][/itex].

I'm having trouble getting the rest of the interval. I thought about covering the set and using compactness, but was wondering if there was a better way.
 
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You get uniform continuity on compact sets, my friend.
 
ZioX said:
You get uniform continuity on compact sets, my friend.

I'm asking about uniform convergence.

ETA: But the function would be uniformly continuous, giving me delta that works for all x in the interval.

Thanks.
 
ex-xian said:
Suppose f(x) is continuous on [0,1], and that f(1)=0. Prove that [itex]x^n f(x)[/itex] converges uniformly on [0,1] as [itex]n \rightarrow \infty[/itex]

By continuity, if [itex]|x-1|< \delta[/itex] then [itex]|f(x)|< \epsilon[/itex] for [itex]x \in [x_0 ,1][/itex] for some [itex]x_0 \in [0,1][/itex].
What's the point of this?

"If [itex]|x-1|< \delta[/itex] then [itex]|f(x)|< \epsilon[/itex]"

means that for [itex]x \in (1-\delta ,1][/itex], [itex]|f(x)|<\epsilon[/itex]. Why add the part about "for [itex]x \in [x_0, 1][/itex] for some [itex]x_0 \in [0,1][/itex]."?
And there is some N such that if n>N, then [itex]|x^n|<\epsilon[/itex] since [itex]x^n \rightarrow 0[/itex] for [itex]x \in [0,1][/itex].
This isn't true for x=1.
The endpoints work since x^nf(x) is 0 there. So I have an N that works for [itex]\{ 0 \} \cup [x_0, 1][/itex].
What is the definition of uniform convergence?
 

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