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Java example source code file (ExponentialDecayFunction.java)

This example Java source code file (ExponentialDecayFunction.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

exponentialdecayfunction, notstrictlypositiveexception, numberistoolargeexception

The ExponentialDecayFunction.java Java example source code

/*
 * 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-x / b,
 * 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>{@code b = -numCall / ln(valueAtNumCall / initValue)}
     * </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-numCall / b.
     *
     * @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);
    }
}

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