/* dtft.c - DTFT of length-L signal at a single frequency w */#include <cmplx.h>                                   /* complex arithmetic */complex dtft(L, x, w)                                /* usage: X=dtft(L, x, w); */double *x, w;                                        /* \(x\) is \(L\)-dimensional */int L;{       complex z, X;       int n;       z = cexp(cmplx(0, -w));                       /* set \(z=e\sp{-j\om}\) */       X = cmplx(0,0);                               /* initialize \(X=0\) */       for (n=L-1; n>=0; n--)              X = cadd(cmplx(x[n], 0), cmul(z, X));       return X;}