Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / nnet-0.1.13 / logsig.m

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+## Copyright (C) 2007 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{a} = logsig (@var{n})
+## @code{logsig} is a non-linear transfer function used to train
+## neural networks.
+## This function can be used in newff(...) to create a new feed forward
+## multi-layer neural network.
+##
+## @end deftypefn
+
+## @seealso{purelin,tansig}
+
+## Author: Michel D. Schmid
+
+
+function a = logsig(n)
+
+
+  a = 1 ./ (1 + exp(-n));
+  ## attention with critical values ==> infinite values
+  ## must be set to 1! Still the same problem as in "tansig"
+  i = find(!finite(a));
+  a(i) = sign(n(i));
+
+endfunction
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