Show Uniform Convergence of fn to f in Compact Metric Space

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Homework Help Overview

The discussion revolves around demonstrating the uniform convergence of a sequence of continuous functions \( f_n \) to a function \( f \) within a compact metric space \( X \). The original poster presents the problem and expresses uncertainty about the continuity of the limit function \( f \) and its relevance to proving uniform convergence.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of assuming \( f \) is not uniformly continuous and consider constructing sequences based on this assumption. There is also a suggestion of using proof by contradiction to analyze the convergence properties of the functions.

Discussion Status

The discussion is ongoing, with participants sharing their thoughts on potential approaches and questioning the necessity of certain assumptions. Some guidance has been offered regarding the structure of the proof, but no consensus has been reached on the best path forward.

Contextual Notes

There is a focus on the continuity of the limit function \( f \) and its implications for uniform convergence, with participants expressing uncertainty about how these concepts interrelate. The compactness of the space \( X \) is also a critical factor in the discussion.

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Homework Statement


Alright, here is the problem. Given a compact metric space X, and a sequence of functions fn which are continuous and f_{n}:X->R (reals), also f_n->f (where f is an arbitrary function f:X->R). Also, given any convergent sequence in X x_{n}->x, f_{n}(x_{n})->f(x). The problem is to show that fn converges uniformly to f.

The Attempt at a Solution


Alright, I can prove this relatively easily if I can prove that f (the limit function) is continuous. However, I don't know if this is possible, does anyone see a way to do this? Only little hints if you see a way.
 
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Nevermind continuity, I don't think the continuity of f directly matters in this situation. However, maybe a start on the problem would be to assume that f is not uniformly continuous, and then, picking an epsilon e>0, for each n, pick one x in X such that |fn(x)-f(x)|>=e, and so create a sequence of points in X, which then must have a convergent subsequence due to the compactness of X. From there on, I am stumped, even if this is the correct way to solve the problem.
 
I would think proof by contradiction is a good way to go. If the fn do not converge to f uniformly, then for all \epsilon, there exists an infinite subsequence of functions f_{n_k} such that for each such function, there is a point x_{n_k} with |f(x_{n_k})-f_{n_k}(x_{n_k})|>\epsilon

Relabel these sequences as f_k and x_k for convenience. x_k has a convergent subsequence which we will label y_k. Now let f_k just be the functions corresponding to the points y_k

What can you say about |f(y_k)-f_k(y_k)|
 
Haha, took a walk and that's exactly what came to me. I think I had a proof of a similar theorem stuck in my head and wanted to follow that technique.
 

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