A function which is continuous on Z only

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Discussion Overview

The discussion revolves around finding an example of a function defined on the real numbers that is continuous only at the integers. Participants explore various approaches and ideas related to this problem, including functions that are continuous at specific points and modifications of discontinuous functions.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant expresses difficulty in finding a function that is continuous only at the integers.
  • Another suggests starting with a function that is continuous only at the origin and then repeating it, though this raises questions about continuity at other integers.
  • A proposed function is presented, defined piecewise, but uncertainty remains about its correctness and behavior at integers other than zero.
  • Further suggestions include modifying a function that is discontinuous everywhere to achieve continuity at the integers.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a specific function that meets the criteria, and multiple competing ideas and approaches are presented without resolution.

Contextual Notes

There are unresolved questions regarding the continuity of proposed functions at points other than the origin and the integers, as well as the implications of modifying existing functions.

HappyN
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I have spent ages on this final part of a question but don't seem to be going anywhere - any help would be greatly appreciated!

Given a function f:R->R let X be the set of all points at which f is continuous.
Find an example of a function defined on R which is continuous on Z only.
 
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Hi HappyN! :smile:
HappyN said:
Find an example of a function defined on R which is continuous on Z only.

Find a function continuous at the origin only, and then repeat it. :wink:
 
tiny-tim said:
Find a function continuous at the origin only, and then repeat it. :wink:

Thanks, I'm not quite sure what you mean by 'repeat it' though? If a function is only continuous at the origin surely it is not continuous on all Z?
 
So have you found a function continuous at the origin only?
 
HappyN said:
I have spent ages on this final part of a question but don't seem to be going anywhere - any help would be greatly appreciated!

Given a function f:R->R let X be the set of all points at which f is continuous.
Find an example of a function defined on R which is continuous on Z only.

Start with a function that is discontinuous everywhere and see if you can modify it so that it becomes continuous at the integers but nowhere else.
 
Landau said:
So have you found a function continuous at the origin only?

I got f(x)={ x x € Q
{-x otherwise
not sure if that is right though?
 
HappyN said:
I got f(x)={ x x € Q
{-x otherwise
not sure if that is right though?

what happens at integers other than zero?
 
HappyN said:
I got f(x)={ x x € Q
{-x otherwise
not sure if that is right though?

ok, now chop out a bit round the origin, and keep copy-and-pasting it :wink:
 

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