Uniform Convergence of fn(x) in [0,1]?

In summary, the conversation discusses the convergence of the function fn(x) and whether it is uniform or not. It is determined that fn(x) converges pointwise to f(x)=x, but it is not clear if the convergence is uniform. The maximum of |fn(x)-f(x)| is found to be 1/1+n on the interval [0,1], and it is concluded that there is an N that does not depend on x such that for all n>N, 1/1+n gets arbitrarily small. The conversation ends with the clarification that the chosen N should be greater than 1-e/e.
  • #1
math8
160
0
Let fn(x)=nx^2/1+nx ; x lies in [0,1]

Is the convergence uniform?

Since lim as n-->infinity of fn is x, I can see that fn(x) converges pointwise to f(x)= x
But I get stuck when I try to show the convergence is uniform or not.
 
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  • #2
Since you know the limit is f(x)=x, look at |fn(x)-f(x)|. What's the maximum of that function on the interval [0,1]?
 
  • #3
I think the maximum of |fn(x)-f(x)| on [0,1] is 1/1+n. So can I conclude that the convergence is uniform because there is an "N" that doesn't depend on x such that for all n> or eq. to N, 1/1+n gets arbitrarily small?
 
  • #4
math8 said:
I think the maximum of |fn(x)-f(x)| on [0,1] is 1/1+n. So can I conclude that the convergence is uniform because there is an "N" that doesn't depend on x such that for all n> or eq. to N, 1/1+n gets arbitrarily small?

Can you make that conclusion? If I give you an e>0 can you find an N such that 1/(1+n)<e for all n>N? Sure you can. If you're not sure you'd better figure out how pick a corresponding N.
 
  • #5
that N should be > than 1-e/e right?
 
  • #6
math8 said:
that N should be > than 1-e/e right?

Sure. Use parentheses when you write something like (1-e)/e, ok? 1-e/e at first glance looks like 1-(e/e), which looks like 0.
 
  • #7
Right, thanks.
 

1. What is uniform convergence in [0,1]?

Uniform convergence in [0,1] refers to the convergence of a sequence of functions to a limit function on the interval [0,1]. This means that the functions in the sequence approach the limit function at the same rate on the entire interval, rather than just at certain points.

2. How does uniform convergence differ from pointwise convergence?

Pointwise convergence only requires that the functions in a sequence approach the limit function at each individual point, whereas uniform convergence requires that the functions approach the limit function at the same rate on the entire interval.

3. Why is uniform convergence important in mathematical analysis?

Uniform convergence is important because it allows us to guarantee that the limit function of a sequence of functions is continuous, even if the individual functions in the sequence may not be. This makes it a useful tool in proving the convergence of integrals and series.

4. Can a sequence of functions converge uniformly without converging pointwise?

Yes, it is possible for a sequence of functions to converge uniformly without converging pointwise. This means that the functions in the sequence approach the limit function at the same rate on the entire interval, but may not approach the limit function at each individual point.

5. How can uniform convergence be tested on a given interval [a,b]?

One way to test for uniform convergence on an interval [a,b] is to use the Weierstrass M-test. This test involves finding an upper bound for the absolute value of each function in the sequence and then checking if the series formed by these upper bounds converges. If the series converges, then the sequence of functions converges uniformly on the interval [a,b].

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