I'm trying to translate CSound code from the FLOSS manuals for a van der Pol oscillator to make a Pd external. The CSound code is here
http://en.flossmanuals.net/csound/g-physical-modelling/ (you have to scroll down till you reach the van der Pol section). I think I get what's going on there, but the results I get when writing the output to an array, are not the same as the ones provided in th FLOSS manuals.
Here's my perform routine:
t_int *vanDerPol_perform(t_int *w)
{
// Copy the object pointer
t_vanDerPol *x = (t_vanDerPol *) (w[1]);
// Copy signal vector pointers
t_float *frequency = (t_float *) (w[2]);
t_float *factor = (t_float*) (w[3]);
t_float *excitor_freq = (t_float*) (w[4]);
t_float *excitor_amp = (t_float*) (w[5]);
t_float *output = (t_float *) (w[6]);
// Copy the signal vector size
t_int n = w[7];
// Dereference components from the object structure
float twopi = x->x_twopi;
float sr = x->x_sr;
float si = x->x_si;
float si_factor = x->x_sifactor;
float phase = x->x_phase;
float step = (float) EXCITOR_STEPSIZE;
// Local variables
float phase_local;
float drive_sine; // sinewave to excite the oscillator
// van der Pol samples
float aa;
float av = 0;
float ax = 0;
// damping factor
float c;
// Perform the DSP loop
while(n--){
// excitor code
si = *excitor_freq++ * si_factor;
phase_local = phase / step;
drive_sine = cos(phase_local * twopi) * *excitor_amp++;
// van der Pol code
c = 2 - 2 * cos(*frequency++ * twopi / sr);
aa = (-c) * ax + *factor++ * (1 - ax * ax) * av;
av += aa;
ax = ax + av + drive_sine;
*output++ = av;
// update phase
phase += si;
while(phase > step) phase -= step;
while(phase < 0) phase += step;
}
// Update object's variables
x->x_phase = phase;
x->x_si = si;
// Return the next address in the DSP chain
return w + 8;
}