--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/control/system/ss2tf.m	Fri Jan 14 03:50:02 2000 +0000
@@ -0,0 +1,80 @@
+## 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{outputs} =} ss2tf (@var{inputs})
+## @format
+## [num,den] = ss2tf(a,b,c,d)
+## Conversion from tranfer function to state-space.
+## The state space system
+##       .
+##       x = Ax + Bu
+##       y = Cx + Du
+##
+## is converted to a transfer function
+##
+##                 num(s)
+##           G(s)=-------
+##                 den(s)
+##
+## used internally in system data structure format manipulations
+## @end format
+## @end deftypefn
+
+## Author: R. Bruce Tenison <btenison@eng.auburn.edu>
+## Created: June 24, 1994
+## a s hodel: modified to allow for pure gain blocks Aug 1996
+
+function [num, den] = ss2tf (a, b, c, d)
+
+  ## Check args
+  [n,m,p] = abcddim(a,b,c,d);
+  if (n == -1)
+    num = [];
+    den = [];
+    error("ss2tf: Non compatible matrix arguments");
+  elseif ( (m != 1) | (p != 1))
+    num = [];
+    den = [];
+    error(["ss2tf: not SISO system: m=",num2str(m)," p=",num2str(p)]);
+  endif
+
+  if(n == 0)
+    ## gain block only
+    num = d;
+    den = 1;
+  else
+    ## First, get the denominator coefficients
+    den = poly(a);
+
+    ## Get the zeros of the system
+    [zz,g] = tzero(a,b,c,d);
+
+    ## Form the Numerator (and include the gain)
+    if (!isempty(zz))
+      num = g * poly(zz);
+    else
+      num = g;
+    endif
+
+    ## the coefficients must be real
+    den = real(den);
+    num = real(num);
+  endif
+endfunction
+