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Thursday, 18 April 2013

Functions

Can we Find any two Distinct Functions
f:
such that

f(x)=f(x2)

4 comments:

  1. If it is true for all x, then I think it would be f(x)=0.

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  2. In general f(x)=Const

    is one such function.

    ReplyDelete
  3. We can engineer a solution pretty easily here. Consider some m(x) (we'll talk about what this is later).

    Consider
    L(x)=m(4x)+m(2x)+m(x)+m(x2)+m(x8)+...



    It's easy to see that formally speaking L(x/2)=L(x)
    . Now that series I gave seems hopeless at first since it consider values m at 0 and infinity. That is fine, let us consider m(x)=x3ex2. This rapidly goes to 0 as the |x| gets very large, as well as very small. Then substituting that back into the definition of L gives you a function that is periodic with respect to doubling the period (at least over the reals).

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  4. The L(x) in my earlier comment should be L(x)=...m(4x)... that is, it is infinite in both directions

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