Uniform convergence and continuity

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SUMMARY

The discussion centers on the theorem regarding uniform convergence and continuity in metric spaces. It establishes that if a sequence of functions \( f_k : X \to Y \) converges uniformly to a function \( f \) and each \( f_k \) is continuous at a point \( x_0 \), then \( f \) is also continuous at \( x_0 \). An example provided illustrates that pointwise convergence of continuous functions does not guarantee the continuity of the limit function, specifically using \( f_k(x) = x^k \) on the interval [0,1], which converges to a discontinuous limit function.

PREREQUISITES
  • Understanding of metric spaces and their properties
  • Knowledge of uniform and pointwise convergence
  • Familiarity with continuity of functions in mathematical analysis
  • Basic proficiency in limits and function behavior
NEXT STEPS
  • Study the implications of the Arzelà-Ascoli theorem in functional analysis
  • Explore examples of uniform convergence using sequences of continuous functions
  • Learn about the differences between uniform and pointwise convergence in detail
  • Investigate the role of compactness in continuity and convergence theorems
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Mathematics students, particularly those studying real analysis or functional analysis, as well as educators looking to deepen their understanding of convergence concepts and continuity in metric spaces.

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Homework Statement



Theorem:

Let (X,d_X),(Y,d_Y) be metric spaces and let f_k : X \to Y, f :<br /> X \to Y be functions such that
1. f_k is continuous at fixed x_0 \in X for all k \in \mathbb{N}
2. f_k \to f uniformly
then f is continuous at x_0.

Homework Equations



If all f_k are continuous on X and f_k \to f pointwise, then f need not be continuous. Why?

The Attempt at a Solution



I really can't think of an example. Can someone please explain to me why this is so or give me an example?
 
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f_k(x)=x^k on [0,1]. What's the limit f(x)?
 
Dick said:
f_k(x)=x^k on [0,1]. What's the limit f(x)?

The limit f(x) is
<br /> \begin{align*}<br /> f(x) =&amp; 0 \text{ if } 0 \leq x &lt; 1 \\<br /> f(x) =&amp; 1 \text{ if } x = 1<br /> \end{align*}<br />
which is not continuous.

But every f_k(x) = x^k is continuous and converges pointwise to f.

Thank you so much. I never thought about functions like this.
 

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