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#include <stdio.h>
#include <math.h>
#include <chplot.h>
#include <numeric.h>
#define N 256 /* total sample points */
#define M 4 /* sample time, 4 seconds */
int main() {
int i;
array double t[N], f[N], E[N/2], W[N/2+1],y[2][N/2+1];
array double complex F[N], Fp[N/2+1], Fa[N/2+1];
double Ts, Ws;
linspace(t, 0, M);
f = 9*exp(-9*t);
Ts = t[1] - t[0];
Ws = 2*M_PI/Ts;
fft(F,f);
linspace(W,0,N/2);
W = W*Ws/N;
for (i=0; i<N/2+1; i++) {
Fp[i] = F[i]*Ts;
Fa[i] = 9.0/(9+W[i]*complex(0,1));
y[0][i] = abs(Fp[i]);
y[1][i] = abs(Fa[i]);
}
plotxy(W,y,"FFT example","Frequency, Rad/s","|F(w)|, dB");
}
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