Lorenz.h

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/*
        dsp/Lorenz.h
        
        Copyright 2001-4 Tim Goetze <tim@quitte.de>
        
        http://quitte.de/dsp/
 
        Lorenz fractal.
 
*/
/*
        This program is free software; you can redistribute it and/or
        modify it under the terms of the GNU General Public License
        as published by the Free Software Foundation; either version 2
        of the License, or (at your option) any later version.
 
        This program is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        GNU General Public License for more details.
 
        You should have received a copy of the GNU General Public License
        along with this program; if not, write to the Free Software
        Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
        02111-1307, USA or point your web browser to http://www.gnu.org.
*/
 
#ifndef _DSP_LORENZ_H_
#define _DSP_LORENZ_H_
 
namespace DSP {
 
class Lorenz
{
        public:
                double x[2], y[2], z[2];        
                double h, a, b, c;
                int I;
 
        public:
                Lorenz()
                        {
                                h = 0.001;
                                a = 10.0;
                                b = 28.0;
                                c = 8.0 / 3.0;
                        }
 
                /* rate is normalized (0 .. 1) */
                void set_rate (double r)
                        {
                                h = max (.0000001, r * .015);
                        }
 
                void init (double _h = .001, double seed = .0)
                        {
                                I = 0;
 
                                x[0] = .1 + seed - frandom() * .1;
                                y[0] = 0;
                                z[0] = 0;
 
                                /* progress quickly to get a 'stable' system */
                                h = .001; 
                                
                                int n = 10000 + min ((int) (10000 * seed), 10000);
                                for (int i = 0; i < n; ++i)
                                        step();
 
                                h = _h;
                        }
 
                sample_t get()
                        {
                                step();
                                return .5 * get_y() + get_z();
                        }
 
                void step()
                        {
                                int J = I ^ 1;
 
                                x[J] = x[I] + h * a * (y[I] - x[I]);
                                y[J] = y[I] + h * (x[I] * (b - z[I]) - y[I]);
                                z[J] = z[I] + h * (x[I] * y[I] - c * z[I]);
 
                                I = J;
                        }
 
                double get_x()
                        {
                                return .024 * (x[I] - .172);
                        }
 
                double get_y()
                        {
                                return .018 * (y[I] - .172);
                        }
 
                double get_z()
                        {
                                return .019 * (z[I] - 25.43);
                        }
};
 
} /* namespace DSP */
 
#endif /* _DSP_LORENZ_H_ */