sigmoidc.java

JaNet: Java Neural Network Toolkit resume: A well documented toolkit for designing and training, a

////////////////////////////////////////////////////////////////////////////////////  
//  
//  Copyright (C) 1996 L.  Patocchi & W.Gander
//
//  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 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, write to the Free Software  Foundation, Inc., 675 Mass
//  Ave, Cambridge, MA 02139, USA.
//
//  Contacts:
//  
//    Project Supervisor
//      W.Hett       [e-mail]
//  
//    Authors
//      W.Gander     [e-mail]
//      L.Patocchi   [e-mail]
//
//  Documentation can be found at:
//
//      http://www.isbiel.ch/Projects/janet/index.html
//
////////////////////////////////////////////////////////////////////////////////////
//
// File : Sigmoidc.java
//
//////////////////////////////////////////////////////////////////
//
//						Sigmoidc  class
//
//////////////////////////////////////////////////////////////////
//
//	Author:  Patocchi L.
//	Date:    18.09.1996
//	Project: jaNet
//
//	this class perform a transfer function with output domain -1...1
//	with a slope parameter 'c'
//	
//////////////////////////////////////////////////////////////////
//
//	date		who					what
//  18.09.1996	Patocchi L.			creation
/*

              Sigmoid(x)
                 ^
                 |+1  ,-------
                 |   /
                 |  /
                 | /
                 |/
     ------------/-0----------> x
                /|
               / |
              /  |
             /   |
     -------'    |-1



*/

package jaNet.backprop;

class Sigmoidc implements activationFn{

	public double c = 0.001;
	
	public double activation(double x){
		double em = Math.exp(-1.0*x*c);
		double ep = Math.exp(x);
		return (ep-em)/(ep+em);
		//return 2.0/(1.0 + Math.exp((-1.0)*x)) - 1.0;
	}
	
	public double activation1stD(double x){
		double e = Math.exp(x*(1+c));
		return 2.0* e *(1+c) /((1+e)*(1+e));
//		double expX = Math.exp(x);
//		return 2.0 * expX/( (1+expX) * (1+expX) );
	}
	
}