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- /* fft/dft_source.c
- *
- * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Brian Gough
- *
- * 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 3 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
- */
- int
- FUNCTION(gsl_dft_complex,forward) (const BASE data[],
- const size_t stride, const size_t n,
- BASE result[])
- {
- gsl_fft_direction sign = gsl_fft_forward;
- int status = FUNCTION(gsl_dft_complex,transform) (data, stride, n, result, sign);
- return status;
- }
- int
- FUNCTION(gsl_dft_complex,backward) (const BASE data[],
- const size_t stride, const size_t n,
- BASE result[])
- {
- gsl_fft_direction sign = gsl_fft_backward;
- int status = FUNCTION(gsl_dft_complex,transform) (data, stride, n, result, sign);
- return status;
- }
- int
- FUNCTION(gsl_dft_complex,inverse) (const BASE data[],
- const size_t stride, const size_t n,
- BASE result[])
- {
- gsl_fft_direction sign = gsl_fft_backward;
- int status = FUNCTION(gsl_dft_complex,transform) (data, stride, n, result, sign);
- /* normalize inverse fft with 1/n */
- {
- const ATOMIC norm = ONE / (ATOMIC)n;
- size_t i;
- for (i = 0; i < n; i++)
- {
- REAL(result,stride,i) *= norm;
- IMAG(result,stride,i) *= norm;
- }
- }
- return status;
- }
- int
- FUNCTION(gsl_dft_complex,transform) (const BASE data[],
- const size_t stride, const size_t n,
- BASE result[],
- const gsl_fft_direction sign)
- {
- size_t i, j, exponent;
- const double d_theta = 2.0 * ((int) sign) * M_PI / (double) n;
- /* FIXME: check that input length == output length and give error */
- for (i = 0; i < n; i++)
- {
- ATOMIC sum_real = 0;
- ATOMIC sum_imag = 0;
- exponent = 0;
- for (j = 0; j < n; j++)
- {
- double theta = d_theta * (double) exponent;
- /* sum = exp(i theta) * data[j] */
- ATOMIC w_real = (ATOMIC) cos (theta);
- ATOMIC w_imag = (ATOMIC) sin (theta);
- ATOMIC data_real = REAL(data,stride,j);
- ATOMIC data_imag = IMAG(data,stride,j);
- sum_real += w_real * data_real - w_imag * data_imag;
- sum_imag += w_real * data_imag + w_imag * data_real;
- exponent = (exponent + i) % n;
- }
- REAL(result,stride,i) = sum_real;
- IMAG(result,stride,i) = sum_imag;
- }
- return 0;
- }
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