update packages

[CreaPhase.git] / octave_packages / m / signal / fftshift.m

diff --git a/octave_packages/m/signal/fftshift.m b/octave_packages/m/signal/fftshift.m
new file mode 100644 (file)
index 0000000..ccd8194
--- /dev/null
+++ b/octave_packages/m/signal/fftshift.m
@@ -0,0 +1,131 @@
+## Copyright (C) 1997-2012 Vincent Cautaerts
+##
+## This file is part of Octave.
+##
+## Octave 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 3 of the License, or (at
+## your option) any later version.
+##
+## Octave 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 Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn  {Function File} {} fftshift (@var{x})
+## @deftypefnx {Function File} {} fftshift (@var{x}, @var{dim})
+## Perform a shift of the vector @var{x}, for use with the @code{fft}
+## and @code{ifft} functions, in order the move the frequency 0 to the
+## center of the vector or matrix.
+##
+## If @var{x} is a vector of @math{N} elements corresponding to @math{N}
+## time samples spaced by @math{dt}, then
+## @code{fftshift (fft (@var{x}))} corresponds to frequencies
+##
+## @example
+## f = [ -(ceil((N-1)/2):-1:1)*df 0 (1:floor((N-1)/2))*df ]
+## @end example
+##
+## @noindent
+## where @nospell{@math{df}} = 1 / @math{dt}.
+##
+## If @var{x} is a matrix, the same holds for rows and columns.  If
+## @var{x} is an array, then the same holds along each dimension.
+##
+## The optional @var{dim} argument can be used to limit the dimension
+## along which the permutation occurs.
+## @end deftypefn
+
+## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp>
+## Created: July 1997
+## Adapted-By: jwe
+
+function retval = fftshift (x, dim)
+
+  if (nargin != 1 && nargin != 2)
+    print_usage ();
+  endif
+
+  if (nargin == 2)
+    if (! (isscalar (dim) && dim > 0 && dim == fix (dim)))
+      error ("fftshift: dimension DIM must be a positive integer");
+    endif
+    nd = ndims (x);
+    sz = size (x);
+    sz2 = ceil (sz(dim) / 2);
+    idx = cell ();
+    idx = repmat ({':'}, nd, 1);
+    idx{dim} = [sz2+1:sz(dim), 1:sz2];
+    retval = x(idx{:});
+  else
+    if (isvector (x))
+      xl = length (x);
+      xx = ceil (xl/2);
+      retval = x([xx+1:xl, 1:xx]);
+    elseif (ismatrix (x))
+      nd = ndims (x);
+      sz = size (x);
+      sz2 = ceil (sz ./ 2);
+      idx = cell ();
+      for i = 1:nd
+        idx{i} = [sz2(i)+1:sz(i), 1:sz2(i)];
+      endfor
+      retval = x(idx{:});
+    else
+      error ("fftshift: expecting vector or matrix argument");
+    endif
+  endif
+
+endfunction
+
+
+%!test
+%!  x = [0:7];
+%!  y = fftshift (x);
+%!  assert(y, [4 5 6 7 0 1 2 3]);
+%!  assert(fftshift (y), x);
+
+%!test
+%!  x = [0:6];
+%!  y = fftshift (x);
+%!  assert(y, [4 5 6 0 1 2 3]);
+%!  assert(fftshift (y), [1 2 3 4 5 6 0]);
+
+%!test
+%!  x = [0:7]';
+%!  y = fftshift (x);
+%!  assert(y, [4;5;6;7;0;1;2;3]);
+%!  assert(fftshift (y), x);
+
+%!test
+%!  x = [0:6]';
+%!  y = fftshift (x);
+%!  assert(y, [4;5;6;0;1;2;3]);
+%!  assert(fftshift (y), [1;2;3;4;5;6;0]);
+
+%!test
+%!  x = [0:3];
+%!  x = [x;2*x;3*x+1;4*x+1];
+%!  y = fftshift (x);
+%!  assert(y, [[7 10 1 4];[9 13 1 5];[2 3 0 1];[4 6 0 2]]);
+%!  assert(fftshift (y), x);
+
+%!test
+%!  x = [0:3];
+%!  x = [x;2*x;3*x+1;4*x+1];
+%!  y = fftshift (x,1);
+%!  assert(y, [[1 4 7 10];[1 5 9 13];[0 1 2 3];[0 2 4 6]]);
+%!  assert(fftshift (y,1), x);
+
+%!test
+%!  x = [0:3];
+%!  x = [x;2*x;3*x+1;4*x+1];
+%!  y = fftshift (x,2);
+%!  assert(y, [[2 3 0 1];[4 6 0 2];[7 10 1 4];[9 13 1 5]]);
+%!  assert(fftshift (y,2), x);
+