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#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#define _PI 3.14159
#define _N 100
struct ret
{
double *val;
unsigned int valc;
};
static double absolute(double a, double b);
struct ret dft(unsigned long N, double *val);
int main(void)
{
double val[_N];
for(int i = 0; i < _N ; i++)
{
val[i] = 0;
}
for(int i = 0; i < _N; i+=4)
{
val[i] = 1;
}
struct ret a = dft(_N, (double*)&val);
for(int i = 0; i < a.valc; i++)
{
printf("%f,",a.val[i]);
}
printf("\n");
return 0;
}
//discrete fourier transform
// N: Number of values
// *val: Array of values
struct ret dft(unsigned long N, double *val)
{
//Dynamic memory allocation
struct ret _ret;
double kmax = N / 2;
double *ival = malloc(sizeof(double) * kmax); //Array of imaginary values
double *rval = malloc(sizeof(double) * kmax); //Array of real values
_ret.val = malloc(sizeof(double) * kmax);
_ret.valc = kmax;
//Calculate Fourier-Transform for every k
for (unsigned int k = 0; k < kmax; k++)
{
rval[k] = 0;
ival[k] = 0;
//Actual discrete Fourier-Transform
for (unsigned int n = 0; n < N; n++)
{
double angle = (2 * _PI * k * n) / N;
double rx = val[n] * cos(angle);//real part
double ix = - val[n] * sin(angle);//imaginary part
rval[k] += rx;
ival[k] += ix;
}
_ret.val[k] = absolute(rval[k], ival[k]);
}
return _ret;
}
static double absolute(double a, double b)
{
return sqrt(pow(a, 2) + pow(b, 2));
}
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