function retval = ifftshift (V)

%% Copyright (C) 1997 by Vincent Cautaerts
%% 
%% This program is free software; you can redistribute it and/or modify
%% it under the terms of the GNU General Public License as published by
%% the Free Software Foundation; either version 2, or (at your option)
%% any later version.
%% 
%% This program is distributed in the hope that it will be useful, but
%% WITHOUT ANY WARRANTY; without even the implied warranty of
%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
%% General Public License for more details. 
%% 
%% You should have received a copy of the GNU General Public License
%% along with this file.  If not, write to the Free Software Foundation,
%% 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

%% usage: y = ifftshift(W)
%%
%% Performs a shift of the vector V, for use with the "fft" and "ifft"
%% functions, in order the move the frequency 0 to the centre of
%% the vector or matrix.
%%
%% If V is a vector of E datas corresponding to E time samples spaced
%% of Dt each, then fftshift (fft (V)) correspond to frequencies
%%
%%   f = linspace (-E/(4*DT), (E/2-1)/(2*DT), E)
%%
%% If V is a matrix, does the same holds for rows and columns.

%% Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp>
%% Created: July 1997
%% Adapted-By: jwe
%% Converted from fftshift to ifftshift by marius schamschula <marius@caos.aamu.edu>
%% Converted: July 2000

retval = 0;

if (nargin != 1)
	usage ("usage: ifftshift (X)");
end

if (is_vector (V))
    x = length (V);
    xx = floor (x/2);
    retval = V([xx+1:x, 1:xx]);
elseif (is_matrix (V))
    [x, y] = size (V);
    xx = floor (x/2);
    yy = floor (y/2);
    retval = V([xx+1:x, 1:xx], [yy+1:y, 1:yy]);
end

end