Center of n-period hyperbolic component of Mandelbrot set is a point of parameter plane :
which is mapped by multiplier map on the center of unit circle m=0+0*i (in multiplier plane) c: m(c,F,period) = 0
for which periodic orbit is superattractive = multiplier is equal to zero c: ln(c) = 0
We will use second definition to compute centers.
because :
ln(c) = F'M(n,c,Z0)
F'M(Z0,c,n):= 2n*Z0*Z1*.. *Zn-1;
so multiplier of periodic orbit is equal to product of first derivative of Mandelbrot function at periodic points ln(c) = 2n*Z0*Z1*.. *Zn-1
So ln(c) = 0
only if z=0 belongs to periodic orbit
it means that z=0 is periodic point of Mandelbrot function:
F[n, c, z=0] = 0
/* basic funtion = monic and centered complex quadratic polynomial
http://en.wikipedia.org/wiki/Complex_quadratic_polynomial
*/
f(z,c):=z*z+c $
/* iterated function */
fn(n, z, c) :=
if n=1 then f(z,c)
else f(fn(n-1, z, c),c) $
/* roots of Fn are periodic point of fn function */
Fn(n,z,c):=fn(n, z, c)-z $
/* G = irreducible divisors of Fn */
polynomial G :
- roots of G are periodic points of period p ( exactly, not for p and its divisors)
- it's order ( degree ) is slightly lower then degree of Fn
/* Maxima function based on algorithm by Robert Munafo */
(%i2) GiveG(p):=
block(
/* if cc could not be computed then gives empty list */
[f:ifactors(p)],
/* ------------ prime numbers ------------------------------------- */
if (p=1) then g:G(p,0,c)
elseif primep(p) then g:G(p,0,c)/G(1,0,c) /* prime > 1 */
/* ------------ composite numbers ------------------------------------- */
/* PowerOfPrime, for example 9=3*3 */
elseif length(f)=1 then g:G(p,0,c)/G(p/2,0,c)
/* Product Of 2 different Primes */
elseif length(f)=2 and f[1][2]+f[2][2]=2 then g:G(p,0,c)*G(1,0,c)/(G(f[1][1],0,c)*G(f[2][1],0,c))
/* p=q*r*r, a prime times the square of another prime */
elseif length(f)=2 and f[1][2]+f[2][2]=3
/* (Zn(p)*Zn(r))/(Zn(q*r)*Zn(r*r)) */
then g:G(p,0,c)*G(r(p),0,c)/(G(p/r(p),0,c)*G(r(p)*r(p),0,c)),
return(g)
)$
/* New function giving G
t is temporary variable = product of G for (divisors of p) other then p
*/
GiveG[p]:=
block(
[f:divisors(p),t:1],
f:delete(p,f), /* delete p from list of divisors */
if p=1
then return(Fn(p,0,c)),
for i in f do t:t*GiveG[i],
g: Fn(p,0,c)/t,
return(ratsimp(g))
)$
/* degree of Fn is 2^(n-1)*/
d(n):=hipow(expand(Fn(n,0,c)),c);
makelist(d(n),n,1,10);
/* n = [1,2,3,4,5 ,6 ,7 ,8 ,9 ,10]
/* degree of Fn = [1,2,4,8,16,32,64,128,256,512] */
/* degree of G = [1,1,3,6,15,27,63,120] */
/* difference = [0,1,1,2,1 ,5 ,1 ,8] */
/*numberOfCenters=[1,1,3,6,15,27,63,120,252,495] */
G. Álvarez, M. Romera, G. Pastor, F. Montoya, "Determination of Mandelbrot set hyperbolic component centres", Chaos Solitons and Fractals, 9 (1998), 1997-2005. (PDF) - list centers up to 7 period with its sumbolic sequences and Myrberg's method for computing them
Young Hee Geum, Young Ik Kim : An improved computation of component centers in the degree-n bifurcation set.
The Korean Journal of Computational & Applied Mathematics Volume 10 , Issue 1-2 (September 2002) Pages: 63 - 73
2002
Young Hee Geum, Young Ik Kim : A STUDY ON COMPUTATION OF COMPONENT CENTERS IN THE DEGREE- n BIFURCATION SET
International Journal of Computer Mathematics, Volume 80, Issue 2 February 2003 , pages 223 - 232