## Copyright (C) 1996 Auburn University.  All rights reserved.
##
## 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 2, 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, write to the Free
## Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111 USA.

## -*- texinfo -*-
## @deftypefn {Function File} {[@var{c}, @var{tsam}, @var{input}, @var{output}] =} sys2fir (@var{sys})
##
## Extract FIR data from system data structure; see @ref{fir2sys} for
## parameter descriptions.
## @end deftypefn
## @seealso{fir2sys}

## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
## Created: July 1996

function [c, tsam, inname, outname] = sys2fir (sys)

  ## let sys2tf do most of the work

  [num,den,tsam,inname,outname] = sys2tf(sys);

  alph = den(1);                        # scale to get monic denominator
  den = den/alph;
  num = num/alph;
  l = length(den);
  m = length(num);
  if( norm(den(2:l)) )
    sysout(sys,"tf");
    error("denominator has poles away from origin");
  elseif( !is_digital(sys) )
    error("system must be discrete-time to be FIR");
  elseif(m != l)
    warning(["sys2fir: deg(num) - deg(den) = ",num2str(m-l), ...
        "; coefficients must be shifted"]);
  endif
  c = num;
endfunction