new file mode 100644
--- /dev/null
+++ b/scripts/control/system/is_sample.m
@@ -0,0 +1,32 @@
+## 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{retval} =} is_sample (@var{Ts})
+## return true if @var{Ts} is a valid sampling time
+## (real,scalar, > 0)
+## @end deftypefn
+
+## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
+## Created: July 1995
+
+function out = is_sample (Ts)
+
+  out = (is_scalar(Ts) && (Ts == abs(Ts)) && (Ts != 0) );
+
+endfunction