calc_complex_fourier.c

/*----------------------------------------------------------------------------

複素指数関数を使った離散フーリエ変換と逆離散フーリエ変換

discrete Fourier transform and inverse discrete Fourier transform

using complex exponential function

calc_complex_fourier.c 

----------------------------------------------------------------------------*/

#include "complex_DFT.h"

// 複素指数関数を使った離散フーリエ変換

// データxを入力し、フーリエ係数Fを出力

// discrete Fourier transform using complex exponential function

// input the data x, output the Fourier coefficient F

void complex_fourier( int num, complex *x, complex *F )

{

int k, n;

double angle;

double complex sum;

for( k = 0; k < num; k++ ) {

sum = 0.0;

for( n = 0; n < num; n++ ) {

angle = ( -2.0 * M_PI * n * k )/(double)num;

sum += x[n] * cexp( angle * I );

}

F[k] = sum;

}

}

/*----------------------------------------------------------------------*/

// 複素指数関数を使った離散逆フーリエ変換

// フーリエ係数Fを入力し、データxを出力

// discrete inverse Fourier transform using complex exponential function

// input the Fourier coefficient F, output the data x

void complex_inv_fourier( int num, complex *x, complex *F )

{

int k, n;

double angle;

double complex sum;

for( n = 0; n < num; n++ ) {

sum = 0.0;

for( k = 0; k < num; k++ ) {

angle = ( 2.0 * M_PI * n * k )/(double)num;

sum += F[k] * cexp( angle * I );

}

x[n] = sum/(double)num;

}

}