Uniform Convergence: Showing It's Not Pointwise Convergent

Click For Summary
A sequence of functions can be pointwise convergent without being uniformly convergent, as demonstrated by counterexamples like the "growing steeples." Pointwise convergence does not guarantee convergence to a continuous function, and the interchange of limits with derivatives or integrals is not valid in such cases. The discussion emphasizes the importance of understanding the distinction between pointwise and uniform convergence. Feedback on these concepts is sought for better preparation for finals. Understanding these nuances is crucial for mastering convergence in functional analysis.
happyg1
Messages
304
Reaction score
0
Hi,
I'm studying for finals and I just need some feedback.
One of questions MIGHT be:
If I know a sequence of functions is pointwise convergent, how do I show that it's not uniformly convergent?
I think that a pointwise convergent sequence of functions might not converge to a continuous function, although it might.
Also, you can't interchange the limit and the derivitive, or the limit and the integral.
Am I right? Am I missing something?
Any feedback will be appreciated.
Thanks,
CC
 
Physics news on Phys.org
Find a counterexample. A standard example involves growing steeples, i.e. the nth function is 0 everywhere except on [2n,2n+2], say, and on this interval, it is basically an isoceles triangle with its value at 2n and 2n+2 being 0, and its value at 2n+1 being n, say.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

Similar threads

Replies
26
Views
2K
  • · Replies 18 ·
Replies
18
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 16 ·
Replies
16
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K