A function which is continuous on Z only

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SUMMARY

The discussion centers on finding a function defined on R that is continuous only at the integers (Z). A proposed solution is the function f(x) defined as f(x) = x for rational numbers (Q) and f(x) = -x otherwise. Participants suggest modifying a discontinuous function to achieve continuity at the integers while remaining discontinuous elsewhere. The challenge includes ensuring the function is continuous specifically at the origin and then replicating this behavior across the integer set.

PREREQUISITES
  • Understanding of real-valued functions f:R->R
  • Knowledge of continuity and discontinuity in mathematical functions
  • Familiarity with rational (Q) and irrational numbers
  • Basic concepts of modifying functions to achieve desired properties
NEXT STEPS
  • Research the properties of discontinuous functions and their modifications
  • Explore examples of functions continuous at specific points, such as the origin
  • Study the implications of continuity on rational and irrational numbers
  • Investigate piecewise functions and their applications in continuity
USEFUL FOR

Mathematicians, students studying real analysis, and anyone interested in the properties of continuity in 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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