DTFT of a signal x at a frequency vector w
X = dtft(x, w);
length-L vector of time samples, x = [x(0),x(1),...,x(L-1)]
length-N vector of frequencies in rads/sample, w = [w1,w2,...,wN]
length-N row vector of DTFT values, X = [X(w1),X(w2),...,X(wN)]
dtft(x, w) computes DTFT of signal x at a frequency vector w. evaluates z-transform of x on the unit-circle: X(z) = \sum_{n=0}^{L-1} x(n)z^{-n}, where z=e^{%i\omega} x,w can be entered row-wise or column-wise, they are internally converted to row vectors, w is in units of radians/sample, w = 2*pi*f/fs
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