1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Continuously uniform function proof

  1. Apr 16, 2009 #1
    1. The problem statement, all variables and given/known data

    Let f : (0,1) → (0,1) be a strict growing continuous function. Does f have to be continuously uniform? Please note that its from (0,1) → (0,1) and NOT [0,1] → [0,1]. Please help me with the steps...I have no clue where to start...thanks...
     
  2. jcsd
  3. Apr 16, 2009 #2

    dx

    User Avatar
    Homework Helper
    Gold Member

    Consider the function [tex] f(x) = -1 / (x - 1) [/tex]. Prove that this is a counterexample.
     
    Last edited: Apr 16, 2009
  4. Apr 16, 2009 #3
    Sorry but could you elaborate further? What theorem should I use?
     
  5. Apr 16, 2009 #4

    dx

    User Avatar
    Homework Helper
    Gold Member

    Sorry, the function in my previous post should have been [tex] f(x) = -1 / (x - 1) [/tex]

    You don't need to use any special theorem. Just try drawing a graph of this function, and see if you can prove that it is not uniformly continuous on (0,1).

    If you find that difficult, think about the following easier example. Prove that 1/x is not uniformly continuous on (0,1).
     
  6. Apr 16, 2009 #5
    I find this rather difficult, so I started pursuing the second option you suggested, and found this link as well:
    http://mathcs.org/analysis/reals/cont/answers/contuni1.html

    I can't figure out how you linked my question to the function you were kind to write down for me.
     
  7. Apr 16, 2009 #6

    dx

    User Avatar
    Homework Helper
    Gold Member

    The function I wrote down is the same function except reflected in the y axis, so that it is strictly increasing (a condition in the question), and moved to the right so that the infinity is at 1 instead of at 0.
     
  8. Apr 16, 2009 #7
    I drew the function. It goes to plus minus infinity at x=1. So what does this tell me? That it is not continuously uniform?
     
  9. Apr 16, 2009 #8
    Here is my plot....
     

    Attached Files:

    Last edited: Apr 16, 2009
  10. Apr 16, 2009 #9

    dx

    User Avatar
    Homework Helper
    Gold Member

    You will notice that it is the same as the function 1/x except moved and reflected. You posted a link to a website showing how to prove that 1/x in not uniformly continuous on (0,1), so you can use the same method with slight modifications to prove that this one is not uniformly continuous.
     
  11. Apr 16, 2009 #10
    However, I do not understand why the specify that (0,1) → (0,1) is strict growing continuous function. So this proof is by contradiction?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Continuously uniform function proof
Loading...