--- /dev/null
+## Copyright (C) 1996, 1998, 2000, 2002, 2004, 2005, 2007 Auburn University
+## Copyright (C) 2012 Lukas F. Reichlin <lukas.reichlin@gmail.com>
+##
+## This program 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.
+##
+## This program 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
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{num}, @var{den}] =} zp2tf (@var{zer}, @var{pol}, @var{k})
+## Converts zeros / poles to a transfer function.
+##
+## @strong{Inputs}
+## @table @var
+## @item zer
+## @itemx pol
+## Vectors of (possibly complex) poles and zeros of a transfer
+## function. Complex values must appear in conjugate pairs.
+## @item k
+## Real scalar (leading coefficient).
+## @end table
+## @end deftypefn
+
+## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
+## (With help from students Ingram, McGowan.)
+
+function [num, den] = zp2tf (varargin)
+
+ if (nargin == 0)
+ print_usage ();
+ endif
+
+ [num, den] = tfdata (zpk (varargin{:}), "vector");
+
+endfunction