## Copyright (C) 1996, 1998, 2000, 2003, 2004, 2005, 2006, 2007
##               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 3 of the License, or (at
## your option) any later version.
##
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## 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
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## -*- texinfo -*-
## @deftypefn {Function File} {[@var{zer}, @var{pol}, @var{k}] =} tf2zp (@var{num}, @var{den})
## Converts transfer functions to poles-and-zero representations.
##
## Returns the zeros and poles of the @acronym{SISO} system defined 
## by @var{num}/@var{den}.
## @var{k} is a gain associated with the system zeros.
## @end deftypefn

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

function [zer, pol, k] = tf2zp (num, den)

  if (nargin == 2)
    if (length (den) > 1)
      pol = roots (den);
    else
      pol = [];
    endif

    if (length (num) > 1)
      zer = roots (num);
    else
      zer = [];
    endif
  else
    print_usage ();
  endif

  k = num(1) / den(1);

endfunction