--- /dev/null
+## Copyright (C) 2011 Lukas F. Reichlin
+##
+## This file is part of LTI Syncope.
+##
+## LTI Syncope 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.
+##
+## LTI Syncope 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 LTI Syncope. If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## check alpha for combination methods of grammians
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: December 2011
+## Version: 0.1
+
+function alpha = __modred_check_alpha_gram__ (alpha, key)
+
+ if (! is_real_scalar (alpha))
+ error ("modred: argument '%s' must be a real scalar", key);
+ endif
+
+ if (abs (alpha) > 1)
+ error ("modred: require -1 <= %s <= 1", key);
+ endif
+
+endfunction