| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.commons.math3.ml.neuralnet.sofm.util; |
| |
| import org.apache.commons.math3.exception.NotStrictlyPositiveException; |
| import org.apache.commons.math3.exception.NumberIsTooLargeException; |
| import org.apache.commons.math3.util.FastMath; |
| |
| /** |
| * Exponential decay function: <code>a e<sup>-x / b</sup></code>, |
| * where {@code x} is the (integer) independent variable. |
| * <br/> |
| * Class is immutable. |
| * |
| * @since 3.3 |
| */ |
| public class ExponentialDecayFunction { |
| /** Factor {@code a}. */ |
| private final double a; |
| /** Factor {@code 1 / b}. */ |
| private final double oneOverB; |
| |
| /** |
| * Creates an instance. It will be such that |
| * <ul> |
| * <li>{@code a = initValue}</li> |
| * <li>{@code b = -numCall / ln(valueAtNumCall / initValue)}</li> |
| * </ul> |
| * |
| * @param initValue Initial value, i.e. {@link #value(long) value(0)}. |
| * @param valueAtNumCall Value of the function at {@code numCall}. |
| * @param numCall Argument for which the function returns |
| * {@code valueAtNumCall}. |
| * @throws NotStrictlyPositiveException if {@code initValue <= 0}. |
| * @throws NotStrictlyPositiveException if {@code valueAtNumCall <= 0}. |
| * @throws NumberIsTooLargeException if {@code valueAtNumCall >= initValue}. |
| * @throws NotStrictlyPositiveException if {@code numCall <= 0}. |
| */ |
| public ExponentialDecayFunction(double initValue, |
| double valueAtNumCall, |
| long numCall) { |
| if (initValue <= 0) { |
| throw new NotStrictlyPositiveException(initValue); |
| } |
| if (valueAtNumCall <= 0) { |
| throw new NotStrictlyPositiveException(valueAtNumCall); |
| } |
| if (valueAtNumCall >= initValue) { |
| throw new NumberIsTooLargeException(valueAtNumCall, initValue, false); |
| } |
| if (numCall <= 0) { |
| throw new NotStrictlyPositiveException(numCall); |
| } |
| |
| a = initValue; |
| oneOverB = -FastMath.log(valueAtNumCall / initValue) / numCall; |
| } |
| |
| /** |
| * Computes <code>a e<sup>-numCall / b</sup></code>. |
| * |
| * @param numCall Current step of the training task. |
| * @return the value of the function at {@code numCall}. |
| */ |
| public double value(long numCall) { |
| return a * FastMath.exp(-numCall * oneOverB); |
| } |
| } |