## Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2002, 2003, 2005,
##               2007 Friedrich Leisch
##
## 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.
##
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## 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} {} autocov (@var{x}, @var{h})
## Return the autocovariances from lag 0 to @var{h} of vector @var{x}.
## If @var{h} is omitted, all autocovariances are computed.
## If @var{x} is a matrix, the autocovariances of each column are
## computed.
## @end deftypefn

## Author: FL <Friedrich.Leisch@ci.tuwien.ac.at>
## Description: Compute autocovariances

function retval = autocov (X, h)

  [n, c] = size (X);

  if (isvector (X))
    n = length (X);
    c = 1;
    X = reshape (X, n, 1);
  endif

  X = center (X);

  if (nargin == 1)
    h = n - 1;
  endif

  retval = zeros (h + 1, c);

  for i = 0 : h
    retval(i+1, :) = diag (X(i+1:n, :).' * conj (X(1:n-i, :))).' / n;
  endfor

endfunction