Functions that vanish at integers

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Discussion Overview

The discussion revolves around identifying functions that vanish at integer values, with a focus on both one-dimensional and potential higher-dimensional generalizations. Participants explore the characteristics and possibilities of such functions, including their continuity and construction methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the function f(x) = sin(2*pi*x) vanishes at all integers and inquire about other similar functions and their generalizations.
  • One participant suggests that without a specific definition, the range of functions that vanish at integers is limited, proposing a function that equals a constant for non-integer values and zero for integers.
  • Another participant humorously claims there are "as many as you can draw," implying a vast number of such functions exist.
  • A later reply questions the notion of a limited number of functions, suggesting that the idea of "function" should not be restricted to simple formulas.
  • Participants discuss the possibility of constructing functions f(x,y) that vanish at integer pairs, exploring combinations of existing functions.
  • One participant emphasizes that continuity is not a requirement, allowing for more flexibility in defining functions that meet the criteria.

Areas of Agreement / Disagreement

There is no consensus on the number or nature of functions that vanish at integers. Some participants believe there are many possibilities, while others suggest a more limited range exists based on specific definitions.

Contextual Notes

Participants express varying assumptions about the continuity of functions and the definitions of what constitutes a function, leading to differing perspectives on the topic.

imAwinner
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We know that the function f(x) = sin(2*pi*x) vanishes at all integers, are there other functions like that and what is the appropriate generalization to higher dimensions?

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This is probably not what you are looking for, but unless you define a function like; f is a function that is equal to some constant y for non-integer values, and 0 for integer values; then you will find there is a very limited range of functions you can have.

You could also just put an integer K into the argument on the sine. And put any constant outside the sine.
 
There are as many as you can draw. And more.
 
ZioX said:
There are as many as you can draw. And more.

i don't no... i can draw like a hundred of those... and id ont think there are more than that...









:-p
 
Maybe I wasn't specific, I'm looking for the formula of a function f(x,y) that would vanish at integers, could anyone help?
 
imAwinner said:
We know that the function f(x) = sin(2*pi*x) vanishes at all integers, are there other functions like that and what is the appropriate generalization to higher dimensions?

For one-dimensional functions [itex]f(x): \mathbb{R}\to\mathbb{R}[/itex], there are
[tex]\beth_1^{\beth_1}=\beth_2=2^{2^{\aleph_0}}[/tex] ("lots")
of functions that vanish on the integers.
 
imAwinner said:
Maybe I wasn't specific, I'm looking for the formula of a function f(x,y) that would vanish at integers, could anyone help?

Suppose we had two such real valued functions on the reals. What new function could you create such that its restriction on Z^2 is identically zero and nonzero on R^2/Z^2?
 
Last edited:
First of all note that you haven't required that the functions be continuous so you can pretty much pick any values you want for non-integer x and require f(n) be 0 for integer n. How about f(x)= 1 if x is not an integer, 0 if x is an integer?

Even requiring continuous, it is always possible to be whatever (constant) value you want between n and -n and and add a section for x between [itex]n- \epsilon[/itex] and n (for very small [itex]\epsilon[/itex] to drop continuously to 0 at n. And there is certainly no reason to require that f not be very complicated between integers.

If you don't think there are more than "hundreds" of such functions (or if you think of functions as limited to "formulas") then you have a very restricted idea of "function".
 
HallsofIvy said:
If you don't think there are more than "hundreds" of such functions (or if you think of functions as limited to "formulas") then you have a very restricted idea of "function".

Before there's any confusion, the "hundred" comment is mine (in jest).
 

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