411 REFERENCE · Wikibooks
Fractals/Mathematics/Period
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
external angle
All rays landing at the same periodic point have the same period: the common period of the rays is a (possibly proper) multiple of the period of their landing point; therefore one distinguishes: the ray period from the orbit period.H. Bruin and D. Schleicher, Symbolic dynamics of quadratic polynomials, Institut Mittag-Leffler, The Royal Swedish Academy of Sciences, 7.
The doubling map
How to find the period of angle under doubling map
visual
numerical
read period from denominator of decimal fraction ( reduced rational fraction m/n )
find period/preperiod in the binary expansion ( binary sequence)
string matching algorithms, for instance, naive or brute-force search, Knuth-Morris-Pratt algorithmmath stackexchange question: period-of-a-finite-binary-sequence
discrete Fourier transform
read it from the itinerary of angle under doubling map
Period of binary expansion of reduced rational fraction m/n is equal to the multiplicative order of 2 modulo n:
C version
double precision: forward and inverse doubling map
/*
doubling map
en.wikipedia.org/wiki/Dyadic_transformation
2*t mod 1
how to invert doubling map
Inverse of doubling map is multivalued function: 2 preimages
t/2 and (t+1)/2
to choose proper preimage one needs extra information from forward iteration = itinerary
itinerary : list of symbols
for coding the orbits of a given dynamical system
by partitioning the space X and forming an itinerary
http://www.maths.qmul.ac.uk/~sb/cf_chapter4.pdf
see also how to convert proper decimal fraction to binary fraction
commons.wikimedia.org/wiki/File:Binary_decomposition_of_dynamic_plane_for_f0(z)_%3D_z%5E2.png
---------- git --------------------
cd existing_folder
git init
git remote add origin git@gitlab.com:adammajewski/doubling_map.git
git add .
git commit -m "Initial commit"
git push -u origin master
*/
#include <stdio.h> // printf
#include <math.h> // fabs
#define iMax 8 //
int main(){
double t0 ;
double t ;
double ti; // final t after iMax iterations
double tr; //
double dt;
int itinerary[iMax]= {0};
int i;
t0 = (double) 1/7;
t = t0;
// check the input : it should be 0.0 <= t < 1.0
if (t>1.0) {printf("t is > 1.0\n"); return 1;}
if (t<0.0) {printf("t is < 0.0\n"); return 1;}
printf("forward iteration of doubling map\n");
for(i=0; i<iMax; i++){
printf("t%d = %f", i, t);
// https://en.wikipedia.org/wiki/Dyadic_transformation
t = t*2.0; // doubling
if (t>1.0) {
itinerary[i]= 1;
t = t - 1.0;
printf(" wrap\n");} // modulo 1
else printf("\n");
}
printf("t%d = %f\n", i, t);
//
ti = t;
printf("\nbackward iteration of doubling map = halving map \n");
//
for(i=iMax; i>0; i--){ // reverse counting
printf("t%d = %f", i, t);
if (itinerary[i-1]==1) { // i-1 !!!
t = t + 1.0;
printf(" unwrap\n");} // modulo 1
else printf("\n");
t = t/2.0; // halving
}
printf("t%d = %f\n", i, t);
tr = t;
//
printf("\n\nresults \n");
printf("t0 = %f\n", t0);
printf("t%d = %f\n", iMax, ti);
dt = fabs(t0- tr);
printf("tr = %f\n", tr);
printf("dt = fabs(t0- tr) = %f\n", dt );
printf("\nitinerary:\n");
for(i=0; i<iMax; i++) printf("itinerary[%d] = %d \n", i, itinerary[i]);
printf("\ndecimal %f has binary expansion = 0.", t0);
for(i=0; i<iMax; i++) printf("%d", itinerary[i]);
printf("\n");
if (dt < 0.0000000001) printf("program works good !\n");
else printf("program fails !\n");
return 0;}
arbitrary precision
// gcc d.c -lgmp -Wall
#include <stdio.h>
#include <gmp.h>
// a multiple precision integer, as defined by the GMP library. The C data type for such integers is mpz_t
int print_z(mpz_t z, int base, char *s){
printf("%s= ", s);
mpz_out_str (stdout, 10, z);
printf (" for base = %d\n", base);
return 0;
}
// rop = (2*op) mod 1
// wikipedia : dyadic_transformation or doubling map
void mpq_doubling(mpq_t rop, const mpq_t op)
{
mpz_t n; // numerator
mpz_t d; // denominator
mpz_inits(n, d, NULL);
//
mpq_get_num (n, op); //
mpq_get_den (d, op);
// n = (n * 2 ) % d
mpz_mul_ui(n, n, 2);
mpz_mod( n, n, d);
// output
mpq_set_num(rop, n);
mpq_set_den(rop, d);
mpz_clears(n, d, NULL);
}
int main ()
{
int i;
//
unsigned long int e = 89; // exponent is also a period of doubling map
unsigned long int b = 2;
// arbitrary precision variables from GMP library
mpz_t n ; // numerator of q
mpz_t d ; // denominator of q
mpq_t q; // rational number q = n/d
// init and set variables
mpz_init_set_ui(n, 1);
// d = (2^e) -1
// http://fraktal.republika.pl/mset_external_ray.html
mpz_init(d);
mpz_ui_pow_ui(d, b, e) ; // d = b^e
mpz_sub_ui(d, d, 1); // d = d-1
// q = n/d
mpq_init (q); //
mpq_set_num(q,n);
mpq_set_den(q,d);
mpq_canonicalize (q); // It is the responsibility of the user to canonicalize the assigned variable before any arithmetic operations are performed on that variable.
// print
//print_z(d, 10, "d ");
//print_z(n, 10, "n ");
gmp_printf ("q = %Qd\n",q); //
//
for (i=0; i<(1+2*e) ; i++){
mpq_doubling(q, q);
gmp_printf ("q = %Qd\n",q); //
}
// clear memory
mpq_clear (q);
mpz_clears(n, d, NULL);
return 0;
}
C++ version
/*
based on :
mndcombi.cpp by Wolf Jung (C) 2010.
http://mndynamics.com/indexp.html
which is the part of Mandel 5.5
multiplatform C++ GUI program using QT
on the same licence as above
"The function is computing the preperiod and period (of n/d under doubling map)
and setting the denominator to 2^preperiod*(2^period - 1) if possible.
So 1/5 becomes 3/15 and 2/10 becomes 3/15 as well.
The period is returned as the value of the function,
n and d are changed ( Arguments passed to function by reference)
and the preperiod is returned in k." (Wolf Jung)
Question : if result is >=0 why do not use unsigneg char or unsigned int for type of result ???
*/
int normalize(unsigned long long int &n, unsigned long long int &d, int &k)
{ if (!d) return 0; // d==0 error
n %= d;
while (!(n & 1) && !(d & 1)) { n >>= 1; d >>= 1; }
int p;
unsigned long long int n0, n1 = n, d1 = d, np;
k = 0;
while (!(d1 & 1)) { k++; d1 >>= 1; if (n1 >= d1) n1 -= d1; }
n0 = n1;
for (p = 1; p <= 65 - k; p++)
{ twice(n1, d1);
if (n1 == n0) break; }
if (k + p > 64) return 0; // more then max unsigned long long int
np = 1LL;
np <<= (p - 1);
np--; np <<= 1;
np++; //2^p - 1 for p <= 64
n0 = np;
d >>= k; n1 = d;
if (n1 > n0) { n1 = n0; n0 = d; }
while (1) { d1 = n0 % n1; if (!d1) break;
n0 = n1; n1 = d1; } //gcd n1
n /= d/n1;
n *= np/n1;
d = np << k;
return p;
}
Lisp version
(defun give-period (ratio-angle)
"gives period of angle in turns (ratio) under doubling map"
(let* ((n (numerator ratio-angle))
(d (denominator ratio-angle))
(temp n)) ; temporary numerator
(loop for p from 1 to 100 do
(setq temp (mod (* temp 2) d)) ; (2 x n) modulo d = doubling)
when ( or (= temp n) (= temp 0)) return p )))
Maxima CAS version
DoublingMap(r):=
block([d,n],
n:ratnumer(r),
d:ratdenom(r),
mod(2*n,d)/d)$
/*
Tests :
GivePeriod (1/7)
3
GivePeriod (1/14)
0
GivePeriod (1/32767)
15
GivePeriod (65533/65535)
16
Gives 0 if :
* not periodic ( preperiodic )
* period >pMax
*/
GivePeriod (r):=
block([rNew, rOld, period, pMax, p],
pMax:100,
period:0,
p:1,
rNew:DoublingMap(r),
while ((p<pMax) and notequal(rNew,r)) do
(rOld:rNew,
rNew:DoublingMap(rOld),
p:p+1
),
if equal(rNew,r) then period:p,
period
);
Haskell version
Haskell versionlavaurs' algorithm in Haskell with SVG output by Claude Heiland-Allen
Conversion from an integer type (Int or Integer) to anything else is done by "fromIntegral". The target type is inferred automatically
-- by Claude Heiland-Allen
-- import Data.List (findIndex, groupBy)
-- type N = Integer
-- type Q = Rational
period :: Q -> N
period p =
let Just i = (p ==) `findIndex` drop 1 (iterate double p)
in fromIntegral i + 1
Real quadratic map
Complex quadratic map
island
distortion of the island
centers of componenets
math.stackexchange question: function-to-calculate-the-period-of-a-mandelbrot-set-point
What c parameters are hard cases when computing period ?
boundary and near boundary points ( parabolic, Siegel, Cremer)
"for example, c=1/4−10^{−10} takes over 800000 iterations to reach a fixed point in double precision floating point, but 20 iterations of Newton's method suffice to reach a fixed point. The two fixed points are slightly different, but both are fixed (each to themselves) in double precision." - Claude Heiland-Allen
" You may need very small epsilon and very large n, otherwise for example c=−3/4+10{−10} will probably give an incorrect period of 2 instead of the correct period of 1, which error will compound to an incorrect interior distance estimate (for example distance 3.8e-8 with your method (epsilon 1e-12, n 79,573,343) instead of 2e-10 with my method). " Claude Heiland-Allen
"one can iterate a "whole lot" of times, then see if the last iteration equals any of the previous iterations. However, such methods are never foolproof. Typically, they fail when used on points that are comparatively close to the boundary of their mu-atom. In such cases the algorithm will usually "find" an integer multiple of the actual period. This happens because as you get close to a child mu-atom, the points approaching the limit cycle converge in a spiral or pinheel-like manner. For example, imagine the period is actually 5, and our point is close to a child mu-atom with period 35. If you look at each 5th iterate, you'll typically find a pattern that spirals in on a limit point, taking 7 steps to go each time around the spiral. Because of the spiral pattern, the 7th step (35th iteration) is a lot closer than the 1st step (5th iteration), and simple period-finding algorithms will catch the closer one." Robert Munafo From the Mandelbrot Set Glossary and Encyclopedia
Solution:
do not use naive method for computing period by iteration
use Robert P. Munafo's Jordan curve method
finding periodic points for a given period
checking the period using position of parameter = periodicity checking
https://www.shadertoy.com/view/4sdXWX
Period_detection on the parameter plane
Jordan curve method
Period from the Mandelbrot Set Glossary and Encyclopedia, by Robert Munafo, (c) 1987-2017.
periodicity_scan using the box period Jordan curve method by Claude Heiland-Allen
There is a greatly enhanced period detection algorithm (using the jordan curve method) that locates islands in the view even if they are far too small to see at the current magnification level. Robert Munafo
C code from mandelbrot-numerics library by Claude Heiland-Allen
// mandelbrot-numerics -- numerical algorithms related to the Mandelbrot set
// Copyright (C) 2015-2018 Claude Heiland-Allen
// License GPL3+ http://www.gnu.org/licenses/gpl.html
/*
gcc b.c -std=c99 -Wall -Wextra -pedantic -lm
*/
#include <stdio.h> // fprintf
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <complex.h>
#include <math.h>
static inline int sgn(double z) {
if (z > 0) { return 1; }
if (z < 0) { return -1; }
return 0;
}
static inline bool odd(int a) {
return a & 1;
}
static inline double cabs2(double _Complex z) {
return creal(z) * creal(z) + cimag(z) * cimag(z);
}
static inline bool cisfinite(double _Complex z) {
return isfinite(creal(z)) && isfinite(cimag(z));
}
//****************************************************************
//**************** Box period *************************************
//*****************************************************************
static double cross(double _Complex a, double _Complex b) {
return cimag(a) * creal(b) - creal(a) * cimag(b);
}
static bool crosses_positive_real_axis(double _Complex a, double _Complex b) {
if (sgn(cimag(a)) != sgn(cimag(b))) {
double _Complex d = b - a;
int s = sgn(cimag(d));
int t = sgn(cross(d, a));
return s == t;
}
return false;
}
static bool surrounds_origin(double _Complex a, double _Complex b, double _Complex c, double _Complex d) {
return odd
( crosses_positive_real_axis(a, b)
+ crosses_positive_real_axis(b, c)
+ crosses_positive_real_axis(c, d)
+ crosses_positive_real_axis(d, a)
);
}
typedef struct {
double _Complex c[4];
double _Complex z[4];
int p;
} m_d_box_period ;
m_d_box_period *m_d_box_period_new(double _Complex center, double radius) {
m_d_box_period *box = (m_d_box_period *) malloc(sizeof(*box));
if (! box) {
return 0;
}
box->z[0] = box->c[0] = center + ((-radius) + I * (-radius));
box->z[1] = box->c[1] = center + (( radius) + I * (-radius));
box->z[2] = box->c[2] = center + (( radius) + I * ( radius));
box->z[3] = box->c[3] = center + ((-radius) + I * ( radius));
box->p = 1;
return box;
}
void m_d_box_period_delete(m_d_box_period *box) {
if (box) {
free(box);
}
}
bool m_d_box_period_step(m_d_box_period *box) {
if (! box) {
return false;
}
bool ok = true;
for (int i = 0; i < 4; ++i) {
box->z[i] = box->z[i] * box->z[i] + box->c[i];
ok = ok && cisfinite(box->z[i]);
}
box->p = box->p + 1;
return ok;
}
bool m_d_box_period_have_period(const m_d_box_period *box) {
if (! box) {
return true;
}
return surrounds_origin(box->z[0], box->z[1], box->z[2], box->z[3]);
}
int m_d_box_period_get_period(const m_d_box_period *box) {
if (! box) {
return 0;
}
return box->p;
}
int m_d_box_period_do(double _Complex center, double radius, int maxperiod) {
m_d_box_period *box = m_d_box_period_new(center, radius);
if (! box) {
return 0;
}
int period = 0;
for (int i = 0; i < maxperiod; ++i) {
if (m_d_box_period_have_period(box)) {
period = m_d_box_period_get_period(box);
break;
}
if (! m_d_box_period_step(box)) {
break;
}
}
m_d_box_period_delete(box);
return period;
}
//****************************************************************
//**************** Main *************************************
//*****************************************************************
int main(void){
complex double c = -0.120972062945854+0.643951893407125*I; //
complex double dc = 1.0;
int maxiters = 1000;
/* find the period of a nucleus within a large box uses Robert P. Munafo's Jordan curve method */
int p = m_d_box_period_do(c, 4.0 * cabs(dc), maxiters);
fprintf(stdout, "c = %.16f %+.16f \t period = %d\n", creal(c), cimag(c),p);
return 0;
}
Finding period of the orbit
/* mndynamo.cpp by Wolf Jung (C) 2007-2015. Defines classes:
mndynamics, mndsiegel, mndcubesiegel, mndquartsiegel, mndexposiegel,
mndtrigosiegel, mndexpo, mndtrigo, mndmatesiegel, mndmating, mndsingpert,
mndherman, mndnewtonsiegel, mndnewton, mndcubicnewton, mndquarticnewton
These classes are part of Mandel 5.13, which is free software; you can
redistribute and / or modify them under the terms of the GNU General
Public License as published by the Free Software Foundation; either
version 3, or (at your option) any later version. In short: there is
no warranty of any kind; you must redistribute the source code as well.
*/
uint mndynamics::period(double &a, double &b, int cycle) // = 0
{ //determine the period, if cycle then set a, b to periodic point.
uint j; double x, y, x0, y0; critical(a, b, x, y);
for (j = 1; j <= 1000; j++)
{ if (x*x + y*y <= bailout) f(a, b, x, y); else return 0; }
x0 = x; y0 = y;
for (j = 1; j <= 1024; j++)
{ if (x*x + y*y <= bailout) f(a, b, x, y); else return 0;
if ( (x - x0)*(x - x0) + (y - y0)*(y - y0) < 1e-16)
{ if (cycle) { a = x; b = y; }
return j;
}
}
return 10000;
}
Methods :
direct period detection from iterations
the spider algorithm
"methods based on interval arithmetic when implemented properly are capable of finding all period-n cycles for considerable large n." (ZBIGNIEW GALIAS )Rigorous Investigations Of Periodic Orbits In An Electronic Circuit By Means Of Interval Methods by Zbigniew Galias
Floyd's cycle-finding algorithm Mandelbrot set drawing by Milan
Finding period is used to :
draw components of Mandelbrot set
Interior DEM/M
Period of critical orbit
Finding period of critical orbit using forward iteration of critical point :
Maxima CAS
/*
b batch file for maxima
*/
kill(all);
remvalue(all);
/* =================== functions ============ */
/*
https://en.wikibooks.org/wiki/Fractals/Iterations_in_the_complex_plane/qpolynomials
complex quadratic polynomial
*/
f(z,c):=z*z+c;
/* iterated map */
fn(p, z, c) :=
if p=0 then z
elseif p=1 then f(z,c)
else f(fn(p-1, z, c),c);
/*
https://en.wikibooks.org/wiki/Fractals/Mathematics/Period#Complex_quadratic_map
period of c under complex quadratic polynomial f
*/
GivePeriod(c):=block(
[z: 0.0,
k2Max:200, /* to big values couse bind stack overflow */
k1Max:100,
ER:2.0,
dMax:0.0003, /* if too low then gives smaller period then */
period:0 /* no period found = (period > k2Max) or ..... ???? */
],
/* to remove non periodic points , iterate and do not use it */
for k1:1 thru k1Max do
(z: f(z,c),
if (cabs(z)>ER) then (period : -1, /* escaping */
go(exit))
),
/* after k1Max iterations z SHOULD BE inside periodic orbit */
zOld:z,
for k2:1 thru k2Max do
( z: f(z,c),
if (cabs(z)>ER) then (period : -1, go(exit)), /* escaping */
if (cabs(zOld-z)<dMax) then (period : k2, go(exit)) /* periodic */
),
exit,
return(period)
)$
/*
Tests :
good
G(0)
G(-1.75)
G(-1.77)
G(-1.778)
G(-0.155+0.75*%i) period = 3
G(-1.7577+0.0138*%i) period = 9
G(-0.615341000000000 +0.423900000000000*%i); period = 7
G(-1.121550281113895 +0.265176187855967*%i); period = 18)
Tuning :
0 period ( when true period > k2Max
G(-1.119816337988403 +0.264371090395906*%i);
gives 0 when k2Max =100
gives 108 when dMax = 0.003
but true period = 162 ( set k2Max = 200 and dMax= 0.0003
-------------------
G(0.37496784+%i*0.21687214);
http://fraktal.republika.pl/period.html
gives 0
*/
G(c):=GivePeriod(c);
compile(all);
/* -------- input value ------ */
c : 0.25 +0.5 * %i$
/* ============== compute =============== */
p:GivePeriod(c)$
p;
c
code by Claude
Comparison of 2 functions for finding a period :
/*
gcc p.c -Wall -lm
time ./a.out
numerical approximation of period of limit cycle
Adam Majewski
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
long double ER2 = 4.0L;
unsigned int jMax = 1000; // iteration max = Max period
// mndynamics::period(double &a, double &b, int cycle)
// mndynamo.cpp by Wolf Jung (C) 2007-2014
// part of Mandel 5.10 which is free software; you can
// redistribute and / or modify them under the terms of the GNU General
// Public License as published by the Free Software Foundation; either
// version 3, or (at your option) any later version. In short: there is
// no warranty of any kind; you must redistribute the source code as well.
/*
void mndlbrot::f(double a, double b, double &x, double &y) const
{ double u = x*x - y*y + a; y = 2*x*y + b; x = u; }
*/
unsigned int GivePeriodJung(long double cx, long double cy, long double ER2, unsigned int jMax, long double precision2, long double Zp[2])
{ //determine the period, then set Zp to periodic point.
// bailout = ER2 = (EscapeRadius)^2
unsigned int j;
// unsigned int jMax = 500000;
long double x=0.0L;
long double y=0.0L; // z
long double x0, y0; // z0 inside periodic orbit
long double t; // temp
//long double precision = 1e-16;
// iterate until z fall into periodic cycle ( = limit cycle)
for (j = 1; j <= jMax; j++)
{
if (x*x + y*y <= ER2)
{t = x*x - y*y + cx;
y = 2*x*y + cy;
x = t;}
else return 0; //escaping = definitely not periodic
}
// after jMax iterations z SHOULD BE inside periodic orbit
x0 = x; y0 = y; // z = z0
// find a period
for (j = 1; j <= jMax; j++)
{
if (x*x + y*y <= ER2)
{t = x*x - y*y + cx;
y = 2*x*y + cy;
x = t;}
else return 0; // escaping = definitely not periodic
if ( (x - x0)*(x - x0) + (y - y0)*(y - y0) < precision2) // periodic
{ Zp[0] = x;
Zp[1] = y;
return j; // period = j
}
}
return (2*jMax+3); // (not escaping after 2*jMax = maybe periodic but period > jMax) or
// (maybe escaping but slow dynamics, so need more iterations then 2*jMax)
}
int SameComplexValue(long double Z1x,long double Z1y,long double Z2x,long double Z2y, long double precision)
{
if (fabsl(Z1x-Z2x)<precision && fabs(Z1y-Z2y)<precision)
return 1; /* true */
else return 0; /* false */
}
/*-------------------------------*/
// this function is based on program:
// Program MANCHAOS.BAS
// http://sprott.physics.wisc.edu/chaos/manchaos.bas
// (c) 1997 by J. C. Sprott
//
unsigned int GivePeriodS(long double Cx,long double Cy, unsigned int iMax, long double precision, long double Zp[2])
{
long double Zx2, Zy2, /* Zx2=Zx*Zx; Zy2=Zy*Zy */
ZPrevieousX,ZPrevieousY,
ZNextX,ZNextY;
unsigned int i;
unsigned int period = iMax+3; // not periodic or period > iMax
/* dynamic 1D arrays for x, y of z points */
long double *OrbitX; // zx
long double *OrbitY; // zy
int iLength = iMax; // length of arrays ; array elements are numbered from 0 to iMax-1
// creates dynamic arrays and checks if it was done properly
OrbitX = malloc( iLength * sizeof(long double) );
OrbitY = malloc( iLength * sizeof(long double) );
if (OrbitX == NULL || OrbitY ==NULL)
{
printf("Could not allocate memory \n");
return 1; // error
}
Zp[0] = 0.0;
Zp[1] = 0.0;
/* starting point is critical point */
ZPrevieousX=0.0;
ZPrevieousY=0.0;
OrbitX[0] =0.0;
OrbitY[0] =0.0;
Zx2=ZPrevieousX*ZPrevieousX;
Zy2=ZPrevieousY*ZPrevieousY;
/* iterate and save points to the array */
for (i=0;i<iMax ;i++)
{
ZNextY=2*ZPrevieousX*ZPrevieousY + Cy;
ZNextX=Zx2-Zy2 +Cx;
Zx2=ZNextX*ZNextX;
Zy2=ZNextY*ZNextY;
if ((Zx2+Zy2)>ER2) return 0; /* basin of atraction to infinity */
//if (SameComplexValue(ZPrevieousX,ZPrevieousY,ZNextX,ZNextY,precision))
// return 1; /* fixed point , period =1 */
ZPrevieousX=ZNextX;
ZPrevieousY=ZNextY;
/* */
OrbitX[i] = ZNextX;
OrbitY[i] = ZNextY;
};
/* find */
for(i=iMax-2;i>0;i--)
if (SameComplexValue(OrbitX[iMax-1],OrbitY[iMax-1],OrbitX[i],OrbitY[i],precision))
{
Zp[0] = OrbitX[i];
Zp[1] = OrbitY[i];
period = iMax-i-1; // compute period
break; // the loop
}
// free memmory
free(OrbitX);
free(OrbitY);
return period ;
}
unsigned int GivePeriodReal(long double Cx,long double Cy)
{
// check
if ( -0.75L<Cx && Cx<0.25L ) return 1;
if ( -1.25L<Cx && Cx<-0.75L ) return 2;
if ( -1.368089448988708L<Cx && Cx<-1.25L ) return 4; // numerical approximation = maybe wrong
if ( -1.394040000725660L<Cx && Cx<-1.368089448988708L ) return 8; // numerical approximation = maybe wrong
return 0; // -1.36809742955000002314
}
int main()
{
// THE REAL SLICE OF THE MANDELBROT SET
long double CxMin = -1.4011551890L; // The Feigenbaum Point = the limit of the period doubling cascade of bifurcations
long double CxMax = -0.74L;
long double Cx;
long double Cy = 0.0L;
long double PixelWidth = (CxMax-CxMin)/10000.0L;
long double precisionS = PixelWidth / 100.0L;
long double precisionJ = 1e-16;
unsigned int periodS, periodJ, periodR;
long double Zp[2]; // periodic z points on dynamic plane
unsigned int iMax = 1000000; // iteration max = Max period
// text file
FILE * fp; // result is saved to text file
fp = fopen("data2p10pz.txt","w"); // create new file,give it a name and open it in binary mode
fprintf(fp," periods of attracting orbits ( c points ) on real axis of parameter plane = real slice of the Mandelbrot set \n");
fprintf(fp," from Cmin = %.20Lf to Cmax = %.20Lf \n", CxMin, CxMax);
fprintf(fp," dC = CxMax-CxMin = %.20Lf \n", CxMax- CxMin);
fprintf(fp," PixelWidth = %.20Lf \n", PixelWidth);
fprintf(fp," precisionS = %.20Lf ; precisionJ = %.20Lf\n", precisionS, sqrtl(precisionJ));
fprintf(fp," iMaxS = %u ; iMaxJ = %u\n", iMax, 2*jMax);
fprintf(fp," \n\n\n");
// go along real axis from CxMin to CxMax using linear scale
Cx = CxMin;
while (Cx<CxMax)
{
// compute
periodR = GivePeriodReal(Cx,Cy);
periodS = GivePeriodS(Cx, Cy, iMax, precisionS, Zp);
periodJ = GivePeriodJung(Cx, Cy, ER2, jMax, precisionJ, Zp);
// check and save
if (periodR>0)
{
if (periodJ==periodS && periodS==periodR ) // all periods are the same and real period is known
fprintf(fp," c = %.20Lf ; period = %u ; \n", Cx, periodS );
else fprintf(fp," c = %.20Lf ; period = %u ; periodS = %u ; periodJ = %u ; difference !!! \n", Cx, periodR, periodS, periodJ );
}
else // PeriodR==00
{
if (periodJ==0 && periodS==0 )
fprintf(fp," c = %.20Lf ; period = %u ; \n", Cx, periodS );// all periods are the same and real period is known
else { if (periodS==periodJ)
fprintf(fp," c = %.20Lf ; periodJ = periodS = %u ; \n", Cx, periodS );
else fprintf(fp," c = %.20Lf ; periodS = %u ; periodJ = %u ; difference !!! \n", Cx, periodS, periodJ );
}
}
// info message
printf("c = %.20Lf \n",Cx);
// next c point
Cx += PixelWidth;
}
fclose(fp);
printf(" result is saved to text file \n");
return 0;
}
Non-linear scale shows bigger periods ( along real slice of Mandelbrot set ) :
/*
gcc p.c -Wall -lm
time ./a.out
numerical approximation of limit cycle's period
along real slice of Mandelbrot set
Adam Majewski
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// part of THE REAL SLICE OF THE MANDELBROT SET where period doubling cascade is
long double CxMin = -1.4011552; // 1890L; // > The Feigenbaum Point = the limit of the period doubling cascade of bifurcations
long double CxMax = 0.26L;
long double Cx;
long double Cy = 0.0L; // constant value
long double PixelWidth ; // = (CxMax-CxMin)/10000.0L;
//long double precisionS ; //precisionS = PixelWidth / 100.0L;//= PixelWidth / 100.0L;
long double f= 4.669201609102990671853203820466L; // The Feigenbaum delta constant
long double precisionJ = 1e-20;
unsigned int periodJ, periodR;
long double Zp[2]; // periodic z points on dynamic plane
long double ER2 = 4.0L;
unsigned int jMax = 5000000; // iteration max = Max period
unsigned int iNoPeriod;
//unsigned int iMax ; //= 2*jMax; // 1000000; // iteration max = Max period
// mndynamics::period(double &a, double &b, int cycle)
// mndynamo.cpp by Wolf Jung (C) 2007-2014
// part of Mandel 5.10 which is free software; you can
// redistribute and / or modify them under the terms of the GNU General
// Public License as published by the Free Software Foundation; either
// version 3, or (at your option) any later version. In short: there is
// no warranty of any kind; you must redistribute the source code as well.
/*
void mndlbrot::f(double a, double b, double &x, double &y) const
{ double u = x*x - y*y + a; y = 2*x*y + b; x = u; }
code with small changes
*/
unsigned int GivePeriodJung(long double cx, long double cy, long double ER2, unsigned int jMax, long double precision2, long double Zp[2])
{ //determine the period, then set Zp to periodic point.
// bailout = ER2 = (EscapeRadius)^2
unsigned int j;
// unsigned int jMax = 500000;
long double x=0.0L;
long double y=0.0L; // z
long double x0, y0; // z0 inside periodic orbit
long double t; // temp
//long double precision = 1e-16;
// iterate until z fall into periodic cycle ( = limit cycle)
for (j = 1; j <= jMax; j++)
{
if (x*x + y*y <= ER2)
{t = x*x - y*y + cx;
y = 2*x*y + cy;
x = t;}
else return 0; //escaping = definitely not periodic
}
// after jMax iterations z SHOULD BE inside periodic orbit
x0 = x; y0 = y; // z = z0
// find a period
for (j = 1; j <= jMax; j++)
{
if (x*x + y*y <= ER2)
{t = x*x - y*y + cx;
y = 2*x*y + cy;
x = t;}
else return 0; // escaping = definitely not periodic
if ( (x - x0)*(x - x0) + (y - y0)*(y - y0) < precision2) // periodic
{ Zp[0] = x;
Zp[1] = y;
return j; // period = j
}
}
return (iNoPeriod); // (not escaping after 2*jMax = maybe periodic but period > jMax) or
// (maybe escaping but slow dynamics, so need more iterations then 2*jMax)
}
// http://classes.yale.edu/Fractals/MandelSet/MandelScalings/CompDiam/CompDiam.html
unsigned int GivePeriodReal(long double Cx,long double Cy)
{
long double Cx0= 0.25L;
long double Cx1= -0.75L;
long double Cx2= -1.25L;
long double Cx3= -1.368089448988708L; // numerical approximation = maybe wrong
long double Cx4= -1.394040000725660L; // numerical approximation = maybe wrong
if ( Cx1<Cx && Cx<Cx0 ) return 1;
if ( Cx2<Cx && Cx<Cx1 ) return 2;
if ( Cx3<Cx && Cx<Cx2 ) return 4; // numerical approximation = maybe wrong
if ( Cx4<Cx && Cx<Cx3 ) return 8; // numerical approximation = maybe wrong
return 0; // -1.36809742955000002314
}
// try to have the same number of the pixels = n
// inside each hyperbolic component of Mandelbrot set along real axis
// width of components
long double GivePixelWidth(unsigned int period, unsigned int n)
{
long double w ;
unsigned int k;
switch ( period )
{ // A SCALING CONSTANT EQUAL TO UNITY IN 1D QUADRATIC MAPS M. ROMERA, G. PASTOR and F. MONTOYA
case 0 : w=(CxMax-CxMin)/n; break;
case 1 : w=1.000000000000L/n; break; // exact value
case 2 : w=0.310700264133L/n; break; // numerical approximation , maybe wrong
case 4 : w=0.070844843095L/n; break; // w(2*p) = w(p)/f ; f = Feigenbaum constant
case 8 : w=0.015397875272L/n; break;
case 16 : w=0.003307721510L/n; break;
case 32 : w=0.000708881730L/n; break;
case 64 : w=0.000151841994935L/n; break;
case 128 : w=0.000032520887170L/n; break;
case 256 : w=0.00000696502297L/n; break;
case 512 : w=0.000001491696694L/n; break;
case 1024 : w=0.000000319475846L/n; break;
case 2048 : w=0.000000068421948L/n; break;
case 4096 : w=0.000000015L/n; break;
case 8192 : w=0.000000004L/n; break;
case 16384 : w=0.000000001L/n; break;
default : if (period == 2*jMax+3) w=(CxMax-CxMin)/10.0L; // period not found or period > jMax
else { k=period/16384; w = 0.000000001L; while (k>2) { w /=f; k /=2;}; w /=n;} // feigenbaum scaling
}
return w;
}
int main()
{
PixelWidth = (CxMax-CxMin)/1000.0L;
precisionJ = PixelWidth/10000000.0L;
iNoPeriod = 2*jMax+3;
// text file
FILE * fp; // result is saved to text file
fp = fopen("data64_50ff.txt","w"); // create new file,give it a name and open it in binary mode
fprintf(fp," periods of attracting orbits ( c points ) on real axis of parameter plane = real slice of the Mandelbrot set \n");
fprintf(fp," from Cmax = %.20Lf to Cmin = %.20Lf \n", CxMax, CxMin);
fprintf(fp," dC = CxMax-CxMin = %.20Lf \n", CxMax- CxMin);
fprintf(fp," non-inear scale with varied step = PixelWidth \n");
fprintf(fp," precisionJ = %.20Lf\n", sqrtl(precisionJ));
fprintf(fp," jMax = %u\n", 2*jMax);
fprintf(fp," \n\n\n");
// go along real axis from CxMin to CxMax using linear scale
Cx = CxMax;
while (Cx>CxMin)
{
// compute
//periodR = GivePeriodReal(Cx,Cy);
periodJ = GivePeriodJung(Cx, Cy, ER2, jMax, PixelWidth/10000000.0L, Zp);
// check and save
if (periodJ == iNoPeriod)
fprintf(fp," c = %.20Lf ; periodJ = %u ; PixelWidth = %.20LF Period not found : error !!! \n", Cx, periodJ, PixelWidth );
else fprintf(fp," c = %.20Lf ; periodJ = %u ; PixelWidth = %.20LF \n", Cx, periodJ, PixelWidth );
printf("c = %.20Lf ; period = %u \n",Cx, periodJ); // info message
// next c point
PixelWidth =GivePixelWidth( periodJ, 50);
Cx -= PixelWidth;
}
fclose(fp);
printf(" result is saved to text file \n");
return 0;
}
c#
User:Simpsons_contributor: periodicity_checking
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Mandelbrot2
{
public struct MandelbrotData
{
private double px;
private double py;
private double zx;
private double zy;
private long iteration;
private bool inSet;
private HowFound found;
public MandelbrotData(double px, double py)
{
this.px = px;
this.py = py;
this.zx = 0.0;
this.zy = 0.0;
this.iteration = 0L;
this.inSet = false;
this.found = HowFound.Not;
}
public MandelbrotData(double px, double py,
double zx, double zy,
long iteration,
bool inSet,
HowFound found)
{
this.px = px;
this.py = py;
this.zx = zx;
this.zy = zy;
this.iteration = iteration;
this.inSet = inSet;
this.found = found;
}
public double PX
{
get { return this.px; }
}
public double PY
{
get { return this.py; }
}
public double ZX
{
get { return this.zx; }
}
public double ZY
{
get { return this.zy; }
}
public long Iteration
{
get { return this.iteration; }
}
public bool InSet
{
get { return this.inSet; }
}
public HowFound Found
{
get { return this.found; }
}
}
public enum HowFound { Max, Period, Cardioid, Bulb, Not }
class MandelbrotProcess
{
private long maxIteration;
private double bailout;
public MandelbrotProcess(long maxIteration, double bailout)
{
this.maxIteration = maxIteration;
this.bailout = bailout;
}
public MandelbrotData Process(MandelbrotData data)
{
double zx;
double zy;
double xx;
double yy;
double px = data.PX;
double py = data.PY;
yy = py * py;
#region Cardioid check
//Cardioid
double temp = px - 0.25;
double q = temp * temp + yy;
double a = q * (q + temp);
double b = 0.25 * yy;
if (a < b)
return new MandelbrotData(px, py, px, py, this.maxIteration, true, HowFound.Cardioid);
#endregion
#region Period-2 bulb check
//Period-2 bulb
temp = px + 1.0;
temp = temp * temp + yy;
if (temp < 0.0625)
return new MandelbrotData(px, py, px, py, this.maxIteration, true, HowFound.Bulb);
#endregion
zx = px;
zy = py;
int check = 3;
int checkCounter = 0;
int update = 10;
int updateCounter = 0;
double hx = 0.0;
double hy = 0.0;
for (long i = 1; i <= this.maxIteration; i++)
{
//Calculate squares
xx = zx * zx;
yy = zy * zy;
#region Bailout check
//Check bailout
if (xx + yy > this.bailout)
return new MandelbrotData(px, py, zx, zy, i, false, HowFound.Not);
#endregion
//Iterate
zy = 2.0 * zx * zy + py;
zx = xx - yy + px;
#region Periodicity check
//Check for period
double xDiff = Math.Abs(zx - hx);
if (xDiff < this.ZERO)
{
double yDiff = Math.Abs(zy - hy);
if (yDiff < this.ZERO)
return new MandelbrotData(px, py, zx, zy, i, true, HowFound.Period);
} //End of on zero tests
//Update history
if (check == checkCounter)
{
checkCounter = 0;
//Double the value of check
if (update == updateCounter)
{
updateCounter = 0;
check *= 2;
}
updateCounter++;
hx = zx;
hy = zy;
} //End of update history
checkCounter++;
#endregion
} //End of iterate for
#region Max iteration
return new MandelbrotData(px, py, zx, zy, this.maxIteration, true, HowFound.Max);
#endregion
}
private double ZERO = 1e-17;
}
}
References
See also
Cycle detection at wikipedia
Period at wikibooks
Periodic point at wikibooks
Finding period of angle under doubling map
periodic points in wikipedia
Period_detection
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