function [tfd, t, f] = stft4(x, fs, w)% stft4 -- Compute samples of the type IV short-time Fourier transform.%%  Usage%    [tfd, t, f] = stft4(x, fs, w,)%%  Inputs%    x     signal vector%    fs    sampling frequency of x (optional, default is 1 sample/second)%    w     window vector, must be the same length as x (optional, default %          is a gaussian window)%%  Outputs%    tfd   matrix containing the STFT of signal x%    t     vector of sampling times (optional)%    f     vector of frequency values (optional)% Copyright (C) -- see DiscreteTFDs/Copyrightx = x(:);N=length(x);error(nargchk(1, 3, nargin));if (nargin < 2)   fs = 1;endif (nargin < 3)  w = chirplets(N);endw = w(:);w = fftshift(w);M = length(w);if (N ~= M)  error('Signal and window must have the same length!')end% Create a matrix filled with signal values.tfd = zeros(N,N);tfd(:,1) = x;for n = 2:N,  tfd(:,n) = [x(n:N) ; x(1:n-1)];end% Window the data.w = w*ones(1,N);tfd = tfd.*w;% Perform the column ffts to get the stft.tfd = fft(tfd);tfd = tfdshift(tfd)/sqrt(N);t = 1/fs * (0:N-1);f = -fs/2:fs/N:fs/2;f = f(1:N);