/* Copyright: Holger Vogt, 2008
 Generates 1/f noise values according to:
 "Discrete simulation of colored noise and stochastic 
 processes and 1/fa power law noise generation"
 Kasdin, N.J.;
 Proceedings of the IEEE
 Volume 83,  Issue 5,  May 1995 Page(s):802 - 827
*/

#include <math.h>
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdarg.h>			// var. argumente
#include "1-f-code.h"
#include "ngspice.h"

#include "fftext.h"
#include "wallace.h"


void f_alpha(int n_pts, int n_exp, float X[], float Q_d,
float alpha)
{
   int i;
   float *hfa, *wfa;
   float ha;
     
   ha = alpha/2.0f ;
//   Q_d = sqrt(Q_d); /* find the deviation of the noise */
   hfa = TMALLOC(float,n_pts);
   wfa = TMALLOC(float,n_pts);
   hfa[0] = 1.0f;
   wfa[0] = Q_d * (float)GaussWa;
   /* generate the coefficients hk */
   for (i=1 ; i < n_pts; i++) {
      /* generate the coefficients hk */
      hfa[i] = hfa[i-1] * (ha + (float)(i-1)) / ( (float)(i) );
      /* fill the sequence wk with white noise */
      wfa[i] = Q_d * (float)GaussWa;
   }

//   for (i=0 ; i < n_pts; i++)
//      printf("rnd %e, hk %e\n", wfa[i],	hfa[i]);

   /* perform the discrete Fourier transform */
   fftInit(n_exp);
   rffts(hfa, n_exp, 1);
   rffts(wfa, n_exp, 1) ;

   /* multiply the two complex vectors */
   rspectprod(hfa, wfa, X, n_pts);
   /* inverse transform */
   riffts(X, n_exp, 1);

   free(hfa) ;
   free(wfa);
   /* fft tables will be freed in vsrcaccept.c and isrcaccept.c 
   fftFree(); */
   fprintf(stdout,"%d (2e%d) one over f values created\n", n_pts, n_exp);
}