[Octave-bug-tracker] [bug #33683] fftshift documentation and function behavior do not match

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?33683>

                 Summary: fftshift documentation and function behavior do not
match
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Thu 30 Jun 2011 08:56:26 PM UTC
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Installation
                  Status: None
             Assigned to: None
         Originator Name: A. David Trubatch
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.4.0
        Operating System: GNU/Linux

    _______________________________________________________

Details:

fftshift requires a second argument that specifies the dimension along which
the shift is to be made, even if the first argumwent is a one-dimensional
array (i.e., vector). This behavior does not match the documentation (and is
inconsistent with MATLAB) which indicates that fftshift may be called with a
single argument.


Transcript:

octave:1> fftshift([1 2 3 4])
error: fftshift: A(I): index out of bounds; value 4 out of bound 1
error: called from:
error:   /usr/share/octave/3.4.0/m/signal/fftshift.m at line 70, column 14
octave:1> fftshift([1 2 3 4],1)
ans =

   1   2   3   4

octave:2> fftshift([1 2 3 4],2)
ans =

   3   4   1   2

octave:3> fftshift([1 2 3 4]')
error: fftshift: A(I): index out of bounds; value 4 out of bound 1
error: called from:
error:   /usr/share/octave/3.4.0/m/signal/fftshift.m at line 70, column 14
octave:3> fftshift([1 2 3 4]',1)
ans =

   3
   4
   1
   2

octave:4> fftshift([1 2 3 4]',2)
ans =

   1
   2
   3
   4

octave:5> help fftshift
`fftshift' is a function from the file
/usr/share/octave/3.4.0/m/signal/fftshift.m

 -- Function File:  fftshift (X)
 -- Function File:  fftshift (X, DIM)
     Perform a shift of the vector X, for use with the `fft' and `ifft'
     functions, in order the move the frequency 0 to the center of the
     vector or matrix.

     If X is a vector of N elements corresponding to N time samples
     spaced of Dt each, then `fftshift (fft (X))' corresponds to
     frequencies

          f = ((1:N) - ceil(N/2)) / N / Dt

     If X is a matrix, the same holds for rows and columns.  If X is an
     array, then the same holds along each dimension.

     The optional DIM argument can be used to limit the dimension along
     which the permutation occurs.


Additional help for built-in functions and operators is
available in the on-line version of the manual.  Use the command
`doc <topic>' to search the manual index.

Help and information about Octave is also available on the WWW
at http://www.octave.org and via the address@hidden
mailing list.





    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?33683>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/