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Lorenz.h

/*
      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 (.000001, r * .015);
                  }

            void init (double _h = .001, double seed = .0)
                  {
                        I = 0;

                        x[0] = .1 + seed;
                        y[0] = 0;
                        z[0] = 0;

                        /* progress quickly to get a 'stable' system */
                        h = .001; 
                        
                        for (int i = 0; i < 10000; ++i)
                              step();

                        h = _h;
                  }

            d_sample 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_ */

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