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What does it mean to say a point is fixed by f to the m?

Saying a point pp is fixed by fmf^m means that applying the function ff exactly mm times to pp returns pp itself. This rephrases the definition of a periodic point of period mm as a fixed point of the mm-fold iterate of ff.

Conditions

  • ff is a function.
  • mm is a positive integer.
  • pp is a point in the domain of ff.

Reasoning, step by step

  1. Take the definition of a periodic point of period mm: fm(p)=pf^m(p)=p.
  2. Regard the mm-fold iterate fmf^m itself as a new function gg.
  3. Then the equation becomes g(p)=pg(p)=p, which matches the fixed-point form.
  4. Conclude that a point of period mm for ff can be viewed as a fixed point of the iterate fmf^m.

Example

The same idea is restated in a useful form: saying pp has period mm is the same as saying pp is fixed by the iterate fmf^m. This links the new definition back to the original fixed-point equation by replacing ff with fmf^m.

Common misconceptions

  • Thinking that fmf^m means multiplying the function ff by mm.
  • Assuming that a point fixed by fmf^m must also be fixed by ff.

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