## Copyright (C) 2006 Peter V. Lanspeary <pvl@mecheng.adelaide.edu.au>
##
## 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 3 of the License, 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 program; if not, see <http://www.gnu.org/licenses/>.

## Usage:
##   [Pxx,freq] = csd(x,y,Nfft,Fs,window,overlap,range,plot_type,detrend)
##
##     Estimate cross power spectrum of data "x" and "y" by the Welch (1967)
##     periodogram/FFT method.  Compatible with Matlab R11 csd and earlier.
##     See "help pwelch" for description of arguments, hints and references
##     --- especially hint (7) for Matlab R11 defaults.

function varargout = csd(varargin)

  ## Check fixed argument
  if ( nargin<2 )
    error( 'csd: Need at least 2 args. Use help csd.' );
  endif
  nvarargin = length(varargin);
  ## remove any pwelch RESULT args and add 'cross'
  for iarg=1:nvarargin
    arg = varargin{iarg};
    if ( ~isempty(arg) && ischar(arg) && ( strcmp(arg,'power') || ...
           strcmp(arg,'cross') || strcmp(arg,'trans') || ...
           strcmp(arg,'coher') || strcmp(arg,'ypower') ))
      varargin{iarg} = [];
    endif
  endfor
  varargin{nvarargin+1} = 'cross';
  ##
  saved_compatib = pwelch('R11-');
  if ( nargout==0 )
    pwelch(varargin{:});
  elseif ( nargout==1 )
    Pxx = pwelch(varargin{:});
    varargout{1} = Pxx;
  elseif ( nargout>=2 )
    [Pxx,f] = pwelch(varargin{:});
    varargout{1} = Pxx;
    varargout{2} = f;
  endif
  pwelch(saved_compatib);

endfunction
