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+## 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
+