--- /dev/null
+## Copyright (C) 2006 Michel D. Schmid <michaelschmid@users.sourceforge.net>
+##
+##
+## 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 2, 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; see the file COPYING. If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {}[@var{n} = __dtansig (@var{n})
+## first derivative of @code{tansig}
+##
+## @example
+##
+## tansig is a symmetric non linear transfer function
+## used by neural networks.
+## Input n must be calculated with "n = tansig(n)".
+## @end example
+##
+## @end deftypefn
+
+## Author: Michel D. Schmid
+
+
+function a = __dtansig(n)
+
+ a = 1-(n.*n);
+
+endfunction
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