| /* |
| * 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.random; |
| |
| import org.apache.commons.math3.util.FastMath; |
| |
| |
| /** |
| * Generate random vectors isotropically located on the surface of a sphere. |
| * |
| * @since 2.1 |
| */ |
| |
| public class UnitSphereRandomVectorGenerator |
| implements RandomVectorGenerator { |
| /** |
| * RNG used for generating the individual components of the vectors. |
| */ |
| private final RandomGenerator rand; |
| /** |
| * Space dimension. |
| */ |
| private final int dimension; |
| |
| /** |
| * @param dimension Space dimension. |
| * @param rand RNG for the individual components of the vectors. |
| */ |
| public UnitSphereRandomVectorGenerator(final int dimension, |
| final RandomGenerator rand) { |
| this.dimension = dimension; |
| this.rand = rand; |
| } |
| /** |
| * Create an object that will use a default RNG ({@link MersenneTwister}), |
| * in order to generate the individual components. |
| * |
| * @param dimension Space dimension. |
| */ |
| public UnitSphereRandomVectorGenerator(final int dimension) { |
| this(dimension, new MersenneTwister()); |
| } |
| |
| /** {@inheritDoc} */ |
| public double[] nextVector() { |
| final double[] v = new double[dimension]; |
| |
| // See http://mathworld.wolfram.com/SpherePointPicking.html for example. |
| // Pick a point by choosing a standard Gaussian for each element, and then |
| // normalizing to unit length. |
| double normSq = 0; |
| for (int i = 0; i < dimension; i++) { |
| final double comp = rand.nextGaussian(); |
| v[i] = comp; |
| normSq += comp * comp; |
| } |
| |
| final double f = 1 / FastMath.sqrt(normSq); |
| for (int i = 0; i < dimension; i++) { |
| v[i] *= f; |
| } |
| |
| return v; |
| } |
| } |