/* *    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. *//* *    SigmoidUnit.java *    Copyright (C) 2001 University of Waikato, Hamilton, New Zealand */package weka.classifiers.functions.neural;/** * This can be used by the  * neuralnode to perform all it's computations (as a sigmoid unit). * * @author Malcolm Ware (mfw4@cs.waikato.ac.nz) * @version $Revision: 1.6 $ */public class SigmoidUnit  implements NeuralMethod {  /** for serialization */  private static final long serialVersionUID = -5162958458177475652L;    /**   * This function calculates what the output value should be.   * @param node The node to calculate the value for.   * @return The value.   */  public double outputValue(NeuralNode node) {    double[] weights = node.getWeights();    NeuralConnection[] inputs = node.getInputs();    double value = weights[0];    for (int noa = 0; noa < node.getNumInputs(); noa++) {            value += inputs[noa].outputValue(true) 	* weights[noa+1];    }         //this I got from the Neural Network faq to combat overflow    //pretty simple solution really :)    if (value < -45) {      value = 0;    }    else if (value > 45) {      value = 1;    }    else {      value = 1 / (1 + Math.exp(-value));    }      return value;  }    /**   * This function calculates what the error value should be.   * @param node The node to calculate the error for.   * @return The error.   */  public double errorValue(NeuralNode node) {    //then calculate the error.        NeuralConnection[] outputs = node.getOutputs();    int[] oNums = node.getOutputNums();    double error = 0;        for (int noa = 0; noa < node.getNumOutputs(); noa++) {      error += outputs[noa].errorValue(true) 	* outputs[noa].weightValue(oNums[noa]);    }    double value = node.outputValue(false);    error *= value * (1 - value);        return error;  }  /**   * This function will calculate what the change in weights should be   * and also update them.   * @param node The node to update the weights for.   * @param learn The learning rate to use.   * @param momentum The momentum to use.   */  public void updateWeights(NeuralNode node, double learn, double momentum) {    NeuralConnection[] inputs = node.getInputs();    double[] cWeights = node.getChangeInWeights();    double[] weights = node.getWeights();    double learnTimesError = 0;    learnTimesError = learn * node.errorValue(false);    double c = learnTimesError + momentum * cWeights[0];    weights[0] += c;    cWeights[0] = c;     int stopValue = node.getNumInputs() + 1;    for (int noa = 1; noa < stopValue; noa++) {            c = learnTimesError * inputs[noa-1].outputValue(false);      c += momentum * cWeights[noa];            weights[noa] += c;      cWeights[noa] = c;     }  }}