Raymond | dee0849 | 2015-04-02 10:43:13 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Licensed to the Apache Software Foundation (ASF) under one or more |
| 3 | * contributor license agreements. See the NOTICE file distributed with |
| 4 | * this work for additional information regarding copyright ownership. |
| 5 | * The ASF licenses this file to You under the Apache License, Version 2.0 |
| 6 | * (the "License"); you may not use this file except in compliance with |
| 7 | * the License. You may obtain a copy of the License at |
| 8 | * |
| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | * |
| 11 | * Unless required by applicable law or agreed to in writing, software |
| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | * See the License for the specific language governing permissions and |
| 15 | * limitations under the License. |
| 16 | */ |
| 17 | |
| 18 | package org.apache.commons.math.random; |
| 19 | |
| 20 | import org.apache.commons.math.util.FastMath; |
| 21 | |
| 22 | |
| 23 | /** |
| 24 | * Generate random vectors isotropically located on the surface of a sphere. |
| 25 | * |
| 26 | * @since 2.1 |
| 27 | * @version $Revision: 990655 $ $Date: 2010-08-29 23:49:40 +0200 (dim. 29 août 2010) $ |
| 28 | */ |
| 29 | |
| 30 | public class UnitSphereRandomVectorGenerator |
| 31 | implements RandomVectorGenerator { |
| 32 | /** |
| 33 | * RNG used for generating the individual components of the vectors. |
| 34 | */ |
| 35 | private final RandomGenerator rand; |
| 36 | /** |
| 37 | * Space dimension. |
| 38 | */ |
| 39 | private final int dimension; |
| 40 | |
| 41 | /** |
| 42 | * @param dimension Space dimension. |
| 43 | * @param rand RNG for the individual components of the vectors. |
| 44 | */ |
| 45 | public UnitSphereRandomVectorGenerator(final int dimension, |
| 46 | final RandomGenerator rand) { |
| 47 | this.dimension = dimension; |
| 48 | this.rand = rand; |
| 49 | } |
| 50 | /** |
| 51 | * Create an object that will use a default RNG ({@link MersenneTwister}), |
| 52 | * in order to generate the individual components. |
| 53 | * |
| 54 | * @param dimension Space dimension. |
| 55 | */ |
| 56 | public UnitSphereRandomVectorGenerator(final int dimension) { |
| 57 | this(dimension, new MersenneTwister()); |
| 58 | } |
| 59 | |
| 60 | /** {@inheritDoc} */ |
| 61 | public double[] nextVector() { |
| 62 | |
| 63 | final double[] v = new double[dimension]; |
| 64 | |
| 65 | double normSq; |
| 66 | do { |
| 67 | normSq = 0; |
| 68 | for (int i = 0; i < dimension; i++) { |
| 69 | final double comp = 2 * rand.nextDouble() - 1; |
| 70 | v[i] = comp; |
| 71 | normSq += comp * comp; |
| 72 | } |
| 73 | } while (normSq > 1); |
| 74 | |
| 75 | final double f = 1 / FastMath.sqrt(normSq); |
| 76 | for (int i = 0; i < dimension; i++) { |
| 77 | v[i] *= f; |
| 78 | } |
| 79 | |
| 80 | return v; |
| 81 | |
| 82 | } |
| 83 | |
| 84 | } |