/**
* Copyright (C) 2001-2017 by RapidMiner and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapidminer.com
*
* This program is free software: you can redistribute it and/or modify it under the terms of the
* GNU Affero General Public License as published by the Free Software Foundation, either version 3
* 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
* Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License along with this program.
* If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.operator.learner.functions.neuralnet;
import com.rapidminer.example.Example;
/**
* This function represents a linear activation function by calculating the identity function on the
* weighted sum. The linear activation function is usually used for the output layer of regression
* problems.
*
* @author Ingo Mierswa
*/
public class LinearFunction extends ActivationFunction {
private static final long serialVersionUID = 1L;
@Override
public String getTypeName() {
return "Linear";
}
@Override
public double calculateValue(InnerNode node, Example example) {
Node[] inputs = node.getInputNodes();
double[] weights = node.getWeights();
double weightedSum = weights[0]; // bias
for (int i = 0; i < inputs.length; i++) {
weightedSum += inputs[i].calculateValue(true, example) * weights[i + 1];
}
return weightedSum;
}
@Override
public double calculateError(InnerNode node, Example example) {
Node[] outputs = node.getOutputNodes();
int[] numberOfOutputs = node.getOutputNodeInputIndices();
double errorSum = 0;
for (int i = 0; i < outputs.length; i++) {
errorSum += outputs[i].calculateError(true, example) * outputs[i].getWeight(numberOfOutputs[i]);
}
return errorSum;
}
}