| /* |
| * 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.math4.neuralnet.sofm; |
| |
| import org.apache.commons.math4.neuralnet.sofm.util.ExponentialDecayFunction; |
| import org.apache.commons.math4.neuralnet.sofm.util.QuasiSigmoidDecayFunction; |
| |
| /** |
| * Factory for creating instances of {@link NeighbourhoodSizeFunction}. |
| * |
| * @since 3.3 |
| */ |
| public final class NeighbourhoodSizeFunctionFactory { |
| /** Class contains only static methods. */ |
| private NeighbourhoodSizeFunctionFactory() {} |
| |
| /** |
| * Creates an exponential decay {@link NeighbourhoodSizeFunction function}. |
| * It will compute <code>a e<sup>-x / b</sup></code>, |
| * where {@code x} is the (integer) independent variable and |
| * <ul> |
| * <li><code>a = initValue</code> |
| * <li><code>b = -numCall / ln(valueAtNumCall / initValue)</code> |
| * </ul> |
| * |
| * @param initValue Initial value, i.e. |
| * {@link NeighbourhoodSizeFunction#value(long) value(0)}. |
| * @param valueAtNumCall Value of the function at {@code numCall}. |
| * @param numCall Argument for which the function returns |
| * {@code valueAtNumCall}. |
| * @return the neighbourhood size function. |
| * @throws IllegalArgumentException if {@code initValue <= 0}, |
| * {@code valueAtNumCall <= 0}, {@code valueAtNumCall >= initValue} |
| * or {@code numCall <= 0}. |
| */ |
| public static NeighbourhoodSizeFunction exponentialDecay(final double initValue, |
| final double valueAtNumCall, |
| final long numCall) { |
| return new NeighbourhoodSizeFunction() { |
| /** DecayFunction. */ |
| private final ExponentialDecayFunction decay |
| = new ExponentialDecayFunction(initValue, valueAtNumCall, numCall); |
| |
| /** {@inheritDoc} */ |
| @Override |
| public int value(long n) { |
| return (int) Math.rint(decay.applyAsDouble(n)); |
| } |
| }; |
| } |
| |
| /** |
| * Creates an sigmoid-like {@code NeighbourhoodSizeFunction function}. |
| * The function {@code f} will have the following properties: |
| * <ul> |
| * <li>{@code f(0) = initValue}</li> |
| * <li>{@code numCall} is the inflexion point</li> |
| * <li>{@code slope = f'(numCall)}</li> |
| * </ul> |
| * |
| * @param initValue Initial value, i.e. |
| * {@link NeighbourhoodSizeFunction#value(long) value(0)}. |
| * @param slope Value of the function derivative at {@code numCall}. |
| * @param numCall Inflexion point. |
| * @return the neighbourhood size function. |
| * @throws IllegalArgumentException if {@code initValue <= 0}, |
| * {@code slope >= 0} or {@code numCall <= 0}. |
| */ |
| public static NeighbourhoodSizeFunction quasiSigmoidDecay(final double initValue, |
| final double slope, |
| final long numCall) { |
| return new NeighbourhoodSizeFunction() { |
| /** DecayFunction. */ |
| private final QuasiSigmoidDecayFunction decay |
| = new QuasiSigmoidDecayFunction(initValue, slope, numCall); |
| |
| /** {@inheritDoc} */ |
| @Override |
| public int value(long n) { |
| return (int) Math.rint(decay.applyAsDouble(n)); |
| } |
| }; |
| } |
| } |