Finding a Sequence with Limit Set [0,1]

Click For Summary

Homework Help Overview

The problem involves finding a sequence whose set of subsequential limits is the interval [0,1]. Participants are exploring different sequences and their properties related to cluster points.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster suggests using the sequence |\sin n| and questions how to rigorously prove that every point in [0,1] is a cluster point. Other participants propose considering the rationals in [0,1] and suggest alternative sequences like n*sqrt(2) mod 1.

Discussion Status

Participants are actively discussing various sequences and their potential to meet the problem's requirements. Some guidance has been offered regarding the use of rational numbers and their properties, indicating a productive direction in the exploration of the problem.

Contextual Notes

There is a mention of the closure of the rationals in [0,1] and its relation to subsequential limits, as well as a reference to cluster points in the context of |\sin n|. The discussion reflects an ongoing exploration of definitions and properties relevant to the problem.

PingPong
Messages
61
Reaction score
0

Homework Statement


Find a sequence whose set of subsequential limits is the interval [0,1].


Homework Equations


If the sequence does not repeat itself, then any subsequential limit is a cluster point.

The Attempt at a Solution



I've an idea that [itex]|\sin n|[/itex] is a solution to this, but I'm not sure how to prove this.

What I need to show is that, since the sequence I've chosen is non-repeating, then every point in the interval [0,1] is a cluster point. That is, if I take any number in [0,1] and am given an epsilon>0, can I always find an infinite amount of members in the sequence in an epsilon neighborhood around the number? This seems to intuitively work since [itex]|\sin n|[/itex] is all over the interval [0,1] (though not necessarily touching every point in the interval), but can this argument be made more rigorous? Any suggestions?
 
Physics news on Phys.org
What can the rationals in [0,1] do for you?
 
|sin(n)| does almost certainly work. But I don't know an obvious proof of this. Maybe think about an easier example though. How about n*sqrt(2) mod 1? That should be 'all over', too, and maybe easier to deal with. Sorry, but I was just going zzzzz and found your post, so I can't give hints right now.
 
morphism said:
What can the rationals in [0,1] do for you?

Works also, and even easier. Nice.
 
Thanks Dick and Morphism. I feel really silly now - I was trying to make it much too complicated. Obviously, since the closure of [itex]Q\cap [0,1][/itex] is again [0,1], then the subsequential limits of a sequence of rational numbers in that interval (say, in the order given by the Cantor diagonalization process, throwing away those outside the interval) is the interval itself.

As a side note, in my search for information on cluster points, I stumbled upon an article (on JStor, which my university subscribes to, so I won't post the url since most people won't be able to access) that gives a proof that the cluster points of sin n is the interval [-1,1].
 

Similar threads

  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
8
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
Replies
7
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 16 ·
Replies
16
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K