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[Octave-bug-tracker] [bug #33721] fftshift.m Error "index out of bounds"


From: Ulrich
Subject: [Octave-bug-tracker] [bug #33721] fftshift.m Error "index out of bounds"
Date: Wed, 06 Jul 2011 12:46:13 +0000
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_7; de-de) AppleWebKit/533.21.1 (KHTML, like Gecko) Version/5.0.5 Safari/533.21.1

URL:
  <http://savannah.gnu.org/bugs/?33721>

                 Summary: fftshift.m Error "index out of bounds"
                 Project: GNU Octave
            Submitted by: octopus
            Submitted on: Mi 06 Jul 2011 12:46:12 GMT
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: octopus
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.4.0
        Operating System: Mac OS

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Details:

The fftshift function in octave 3.4.0 for Mac OS X is erraneous:


> fftshift([1 2 3 4])
error: fftshift: A(I): index out of bounds; value 4 out of bound 1
error: called from:
error:   /Users/voelu/Documents/Fortbildung/Octave/Skripte/fftshift.m at line
7
3, column 15


Fix:
change the lines 68..

      x = length (x);  
      xx = ceil (x/2);
      retval = x([xx+1:x, 1:xx]);


into


      # Fix: use xl for the length of x
      xl = length (x);  
      xx = ceil (xl/2);
      retval = x([xx+1:xl, 1:xx]);



Here is a fixed version of the fftshift.m - file


## Copyright (C) 1997-2011 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 of @math{Dt} each, then @code{fftshift (fft
## (@var{x}))} corresponds to frequencies
##
## @example
## f = ((1:N) - ceil(N/2)) / N / Dt
## @end example
##
## 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 <address@hidden>
## Created: July 1997
## Adapted-By: jwe
## Fixed-By: octopus

function retval = fftshift (x, dim)

  retval = 0;

  if (nargin != 1 && nargin != 2)
    print_usage ();
  endif

  if (nargin == 2)
    if (!isscalar (dim))
      error ("fftshift: dimension must be an integer scalar");
    endif
    nd = ndims (x);
    sz = size (x);
    sz2 = ceil (sz(dim) / 2);
    idx = cell ();
    for i = 1:nd
      idx{i} = 1:sz(i);
    endfor
    idx{dim} = [sz2+1:sz(dim), 1:sz2];
    retval = x(idx{:});
  else
    if (isvector (x))
      # Error in Version 3.4.0: x must not be overwritten!
      # x = length (x);  
      # xx = ceil (x/2);
      # retval = x([xx+1:x, 1:xx]);
      # Fix: use xl for the length of 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







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