Fractional iteration of a function

In summary, the conversation discusses using a function to recursively create new functions with a similar shape but steeper slope. The concept of fractional iteration is mentioned and the speaker is seeking help with expanding higher-derivative terms in the Taylor expansion. The conversation concludes by mentioning that this is for fun and not for homework.
  • #1
Lord Crc
343
47
I have the following function [tex]\begin{align*}
f(x) &= 6x^5 - 15x^4 + 10x^3 & x &\in [0, 1]
\end{align*}[/tex] and I found that by recursively applying it, that is [itex]f(f(x))[/itex] etc, I can get new functions with the same s-like shape but steeper slope.

I was curious if there was a way to smoothly go from [itex]x[/itex] (ie a line) to [itex]f(x)[/itex] to [itex]f(f(x))[/itex] and beyond, and some Googling told me this is called fractional iteration.

However the Wikipedia page didn't leave me with enough clues for finding the appropriate series. In particular I'm struggling to see how to expand the higher-derivative terms in the Taylor expansion in step 4. Any help with this would be appreciated.

FWIW I did go to university and had a fair share of calculus and linear algebra, but it's some 7+ years ago and I'm rusty these days. Oh and this is purely for fun, not homework.
 
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  • #2

Related to Fractional iteration of a function

What is fractional iteration of a function?

Fractional iteration of a function is a mathematical concept in which a function is repeatedly composed with itself a non-integer number of times. It is an extension of the concept of integer iteration, in which a function is composed with itself a whole number of times.

Why is fractional iteration of a function useful?

Fractional iteration of a function allows for a more precise understanding of the behavior of a function. It can help to reveal patterns and relationships that may not be evident when only considering integer iterations. It also has applications in fields such as dynamical systems, chaos theory, and fractal geometry.

How is fractional iteration of a function calculated?

The most common method for calculating fractional iteration of a function is through the use of the Riemann-Liouville fractional derivative. This involves using a fractional power of the function's derivative, which can be approximated using numerical methods such as Taylor series or continued fractions.

What are some examples of fractional iteration of a function?

One well-known example of fractional iteration is the exponential function, where the fractional iteration is given by the fractional power of the base. Another example is the logistic map, which is commonly used in studying chaotic systems and has a well-defined fractional iteration known as the Feigenbaum function.

What are the limitations of fractional iteration of a function?

One limitation of fractional iteration is that it may not always be well-defined or unique for all functions. Some functions may not have a fractional power, and others may have multiple possible fractional iterations. Additionally, the calculation of fractional iteration can be complex and computationally intensive, making it difficult to use in certain applications.

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