Feigenbaum constants


In mathematics, specifically bifurcation theory, the Feigenbaum constants are two mathematical constants which both express ratios in a bifurcation diagram for a non-linear map. They are named after the physicist Mitchell J. Feigenbaum.

History

Feigenbaum originally related the first constant to the period-doubling bifurcations in the logistic map, but also showed it to hold for all one-dimensional maps with a single quadratic maximum. As a consequence of this generality, every chaotic system that corresponds to this description will bifurcate at the same rate. It was discovered in 1975.

The first constant

The first Feigenbaum constant is the limiting ratio of each bifurcation interval to the next between every period doubling, of a one-parameter map
where is a function parameterized by the bifurcation parameter.
It is given by the limit
where are discrete values of at the -th period doubling.

Names

Non-linear maps

To see how this number arises, consider the real one-parameter map
Here is the bifurcation parameter, is the variable. The values of for which the period doubles, are, etc. These are tabulated below:
The ratio in the last column converges to the first Feigenbaum constant. The same number arises for the logistic map
with real parameter and variable. Tabulating the bifurcation values again:

Fractals

In the case of the Mandelbrot set for complex quadratic polynomial
the Feigenbaum constant is the ratio between the diameters of successive circles on the real axis in the complex plane.
Bifurcation parameter is a root point of period- component. This series converges to the Feigenbaum point = −1.401155...... The ratio in the last column converges to the first Feigenbaum constant.
Other maps also reproduce this ratio, in this sense the Feigenbaum constant in bifurcation theory is analogous to Pi | in geometry and e | in calculus.

The second constant

The second Feigenbaum constant,
is the ratio between the width of a tine and the width of one of its two subtines. A negative sign is applied to when the ratio between the lower subtine and the width of the tine is measured.
These numbers apply to a large class of dynamical systems.
A simple rational approximation is * *.

Properties

Both numbers are believed to be transcendental, although they have not been proven to be so. There also exists no known proof that either constant is irrational.
The first proof of the universality of the Feigenbaum constants carried out by Oscar Lanford in 1982 was computer-assisted. Over the years, non-numerical methods were discovered for different parts of the proof, aiding Mikhail Lyubich in producing the first complete non-numerical proof.