ricker.c

/* Ricker filter */
/*
  Copyright (C) 2004 University of Texas at Austin
  
  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
*/

#include <math.h>

#include <rsf.h>

#include "ricker.h"

static kiss_fft_cpx *shape;

void ricker_init(int nfft   /* time samples */, 
		 float freq /* frequency */,
		 int order  /* derivative order */)
/*< initialize >*/
{
    int iw, nw;
    float dw, w;
    kiss_fft_cpx cw;

    /* determine frequency sampling (for real to complex FFT) */
    nw = nfft/2+1;
    dw = 1./(nfft*freq);
 
    shape = (kiss_fft_cpx*) sf_complexalloc(nw);

    for (iw=0; iw < nw; iw++) {
	w = iw*dw;
	w *= w;

	switch (order) {
	    case 2: /* half-order derivative */
		cw.r = 2*SF_PI/nfft;
		cw.i = iw*2*SF_PI/nfft;
		cw = sf_csqrtf(cw);
		shape[iw].r = cw.r*w*expf(1-w)/nfft;
		shape[iw].i = cw.i*w*expf(1-w)/nfft;
		break;
	    case 0:
	    default:
		shape[iw].r = w*expf(1-w)/nfft;
		shape[iw].i = 0.;
		break;
	}
    }

    sf_freqfilt_init(nfft,nw);
    sf_freqfilt_cset(shape);
}

void ricker_close(void) 
/*< free allocated storage >*/
{
    free(shape);
    sf_freqfilt_close();
}

/* 	$Id$	 */