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

In summary, the conversation is discussing the proof that x^n f(x) converges uniformly on [0,1] as n \rightarrow \infty. The main points are that f(x) is continuous on [0,1] and that x^n \rightarrow 0 for x \in [0,1], which is used to show that x^n f(x) converges uniformly on [0,1]. There is also a discussion about using compact sets and the definition of uniform convergence.
  • #1
sparkster
153
0
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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  • #2
You get uniform continuity on compact sets, my friend.
 
  • #3
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.
 
  • #4
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?
 

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

What is uniform convergence?

Uniform convergence is a type of convergence in which a sequence of functions converges to a limit function in such a way that the convergence is independent of the input value. In other words, the rate of convergence is the same for all points in the domain of the function.

How is uniform convergence different from pointwise convergence?

Pointwise convergence is a type of convergence in which a sequence of functions converges to a limit function at each individual point in the domain. In contrast, uniform convergence requires that the rate of convergence is the same for all points in the domain, rather than just at each individual point.

What are some applications of uniform convergence?

Uniform convergence is a useful concept in the analysis of numerical methods, as it allows for the assessment of the accuracy and efficiency of approximation techniques. It is also important in the study of power series, where it is used to determine the radius of convergence.

How is uniform convergence related to continuity?

Uniform convergence is closely related to continuity. In fact, a sequence of continuous functions converging uniformly to a limit function will result in the limit function being continuous as well. This is because uniform convergence preserves the continuity of a function.

Can a uniformly convergent sequence of functions fail to converge pointwise?

Yes, it is possible for a sequence of functions to converge uniformly but not pointwise. This can occur when the limit function is discontinuous or when the rate of convergence varies at different points in the domain, making it impossible for the sequence to converge pointwise.

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