fftshift1.m

阵列信号处理的工具箱

function Xout = fftshift1(Xin, invShift)

%FFTSHIFT1 Shift DC component to or from center of spectrum for several 1D spektra.
%
%  For vectors, FFTSHIFT1(X) swaps the left and right halves of
%  X.  For matrices, FFTSHIFT1(X) swaps the upper and lower halves.
%  Note, for matrices FFTSHIFT1 differs from FFTSHIFT.
%
%  FFTSHIFT1 is useful for visualizing several 1D Fourier transform with
%  the DC component in the middle of the spectrum.
%
%  FFTSHIFT1 is simliar to the Matlab function FFTSHIFT but not the same.
%  FFTSHIFT works on a 2D spektra and FFTSHIFT1 on several 1D spektra.
%
%  FFTSHIFT1(X,'inv') also swaps the halves of X but should be used
%  before IFFT is used. The DC component is shifted from the center of the
%  spectrum to the ends, suitable as input to IFFT.
%
%See also FFTSHIFT, FFT.

%   *  DBT, A Matlab Toolbox for Radar Signal Processing  *
% (c) FOA 1994-2000. See the file dbtright.m for copyright notice.
%
%  Start        : 980714 Svante Bj鰎klund (svabj).
%  Latest change: $Date: 2000/10/16 15:20:57 $ $Author: svabj $.
%  $Revision: 1.4 $
% *****************************************************************************

if nargin < 2
  invShift = '';
end%if

sx = size(Xin);

if (min(sx) == 1)	% A vector.
  len = max(sx);
  Xin = Xin(:);
  if ((rem(len,2) == 0)) % Even number.
    Xout = [Xin(len/2+1:len); Xin(1:len/2)];
  else 		 % Odd number.
    if (strcmp(invShift,'inv'))
      centerIx = floor(len/2);
    else
      centerIx = ceil(len/2);
    end%if
      Xout = [Xin(centerIx+1:len);Xin(1:centerIx)];
  end%if
  if (sx(2) > 1)
    Xout = Xout.';
  end%if
else			% A matrix.
  len = sx(1);
  if ((rem(len,2) == 0)) % Even number.
    Xout = [Xin(len/2+1:len,:); Xin(1:len/2,:)];
  else 			 % Odd number.
    if (strcmp(invShift,'inv'))
      centerIx = floor(len/2);
    else
      centerIx = ceil(len/2);
    end%if
    Xout = [Xin(centerIx+1:len,:);Xin(1:centerIx,:)];
  end%if
end%if