63 lines
1.5 KiB
C
63 lines
1.5 KiB
C
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/* Copyright: Holger Vogt, 2008
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Generates 1/f noise values according to:
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"Discrete simulation of colored noise and stochastic
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processes and 1/fa power law noise generation"
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Kasdin, N.J.;
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Proceedings of the IEEE
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Volume 83, Issue 5, May 1995 Page(s):802 - 827
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*/
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#include <math.h>
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#include <stdio.h>
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#include <stddef.h>
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#include <stdlib.h>
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#include <stdarg.h> // var. argumente
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#include "1-f-code.h"
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#include "ngspice.h"
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#include "fftext.h"
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#include "wallace.h"
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void f_alpha(int n_pts, int n_exp, float X[], float Q_d,
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float alpha)
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{
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int i;
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float *hfa, *wfa;
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float ha;
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ha = alpha/2.0f ;
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// Q_d = sqrt(Q_d); /* find the deviation of the noise */
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hfa = TMALLOC(float,n_pts);
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wfa = TMALLOC(float,n_pts);
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hfa[0] = 1.0f;
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wfa[0] = Q_d * (float)GaussWa;
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/* generate the coefficients hk */
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for (i=1 ; i < n_pts; i++) {
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/* generate the coefficients hk */
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hfa[i] = hfa[i-1] * (ha + (float)(i-1)) / ( (float)(i) );
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/* fill the sequence wk with white noise */
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wfa[i] = Q_d * (float)GaussWa;
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}
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// for (i=0 ; i < n_pts; i++)
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// printf("rnd %e, hk %e\n", wfa[i], hfa[i]);
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/* perform the discrete Fourier transform */
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fftInit(n_exp);
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rffts(hfa, n_exp, 1);
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rffts(wfa, n_exp, 1) ;
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/* multiply the two complex vectors */
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rspectprod(hfa, wfa, X, n_pts);
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/* inverse transform */
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riffts(X, n_exp, 1);
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free(hfa) ;
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free(wfa);
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/* fft tables will be freed in vsrcaccept.c and isrcaccept.c
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fftFree(); */
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fprintf(stdout,"%d (2e%d) one over f values created\n", n_pts, n_exp);
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}
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