wigner1.m

该工具箱为时频分析中的一类重要变换,离散时频分布的工具箱,其中提供基本算法的程序.可直接应用

function [wig, t, f] = wigner1(x, fs, nfreq)
% wigner1 -- Compute samples of the (type I) Wigner distribution.
%
%  Usage
%    [tfd, t, f] = wigner1(x, fs, nfreq)
%
%  Inputs
%    x      signal vector.  wigner1 assumes that x is sampled at the Nyquist
%           rate and uses sinc interpolation to oversample by a factor of 2.
%           If there are two columns then a cross Wigner distribution is
%           computed.
%    fs     sampling frequency of x (optional, default is 1 sample/second)
%    nfreq  number of samples to compute in the frequency direction, must
%           be at least 2*length(x) (optional, defaults to 2*length(x))
%
%  Outputs
%    tfd  matrix containing the Wigner distribution of signal x.  If x has
%         length N, then tfd will be 2N by 2N. (optional)
%    t    vector of sampling times (optional)
%    f    vector of frequency values (optional)
%
% If no output arguments are specified, then the Wigner distribution is 
% displayed using ptfd(tfd, t, f).

% Copyright (C) -- see DiscreteTFDs/Copyright

N = length(x);

error(nargchk(1, 3, nargin));
if (nargin < 3)
  nfreq = 2*N;
end
if (nargin < 2)
  fs = 1;
end

if (nfreq < 2*N)
  error('nfreq must be at least 2*length(x)')
end

% create the temporal acf for positive tau
acf = lacf1(x);
N = 2*N; % width of acf

% negative tau
acf = [acf ; zeros(nfreq+1-N, N) ; conj(flipud(acf(2:N/2,:)))];
wig = real(fft(acf))/N;
wig = tfdshift(wig);

t = 1/(2*fs) * (0:N-1);
f = -fs/2:fs/nfreq:fs/2;
f = f(1:nfreq);

if (nargout == 0)
  ptfd(wig, t, f);
  clear wig
end