001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018 package org.apache.commons.math.random; 019 020 021 /** 022 * Generate random vectors isotropically located on the surface of a sphere. 023 * 024 * @since 2.1 025 * @version $Revision: 925812 $ $Date: 2010-03-21 11:49:31 -0400 (Sun, 21 Mar 2010) $ 026 */ 027 028 public class UnitSphereRandomVectorGenerator 029 implements RandomVectorGenerator { 030 /** 031 * RNG used for generating the individual components of the vectors. 032 */ 033 private final RandomGenerator rand; 034 /** 035 * Space dimension. 036 */ 037 private final int dimension; 038 039 /** 040 * @param dimension Space dimension. 041 * @param rand RNG for the individual components of the vectors. 042 */ 043 public UnitSphereRandomVectorGenerator(final int dimension, 044 final RandomGenerator rand) { 045 this.dimension = dimension; 046 this.rand = rand; 047 } 048 /** 049 * Create an object that will use a default RNG ({@link MersenneTwister}), 050 * in order to generate the individual components. 051 * 052 * @param dimension Space dimension. 053 */ 054 public UnitSphereRandomVectorGenerator(final int dimension) { 055 this(dimension, new MersenneTwister()); 056 } 057 058 /** {@inheritDoc} */ 059 public double[] nextVector() { 060 061 final double[] v = new double[dimension]; 062 063 double normSq; 064 do { 065 normSq = 0; 066 for (int i = 0; i < dimension; i++) { 067 final double comp = 2 * rand.nextDouble() - 1; 068 v[i] = comp; 069 normSq += comp * comp; 070 } 071 } while (normSq > 1); 072 073 final double f = 1 / Math.sqrt(normSq); 074 for (int i = 0; i < dimension; i++) { 075 v[i] *= f; 076 } 077 078 return v; 079 080 } 081 082 }