## Copyright (C) 1996,1998 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 } { outputs =} tf2zp ( inputs ) 
## @format
##  Converts transfer functions to poles / zeros.
## 
##  [zer,pol,k] = tf2zp(num,den) returns the zeros and poles of the SISO system
##  defined by num/den.  K is a gain associated with the system zeros.
## 
## 
## @end format
## @end deftypefn

function [zer, pol, k] = tf2zp (num, den)
## Written by A. S. Hodel, etc.

  if(nargin == 2)
    if(length(den) > 1)          pol = roots(den);
    else                         pol=[];                   endif
    if(length(num) > 1)         zer = roots(num);
    else                        zer=[];                    endif
  else                    error("Incorrect number of input arguments");
  endif

  [a,b,c,d] = tf2ss(num,den);
  [dum,k] = tzero(a,b,c,d);
endfunction