Feigenbaum constants
In mathematics, specifically bifurcation theory, the Feigenbaum constants and 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. Feigenbaum made this discovery in 1975, and he officially published it in 1978.The first constant
The first Feigenbaum constant or simply Feigenbaum constant is the limiting ratio of each bifurcation interval to the next between every period doubling, of a one-parameter mapwhere is a function parameterized by the bifurcation parameter.
It is given by the limit:
where are discrete values of at the th period doubling.
This gives its numerical value :
- A simple rational approximation is, which is correct to 5 significant values. For more precision use, which is correct to 7 significant values.
- It is approximately equal to, with an error of 0.0047 %.
Illustration
Non-linear maps
To see how this number arises, consider the real one-parameter mapHere 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 quadratic polynomial">Quadratic function">quadratic polynomialthe Feigenbaum constant is the limiting 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 (number)|] in geometry and in calculus.
The second constant
The second Feigenbaum constant or Feigenbaum reduction parameter is given by :It 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, which is correct to 2 significant values. For more precision use × × =, which is correct to 8 significant values.
Properties
Both numbers are believed to be transcendental, although they have not been proven to be so. In fact, there is no known proof that either constant is even irrational.The first proof of the universality of the Feigenbaum constants was carried out by Oscar Lanford—with computer-assistance—in 1982. 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.