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Diffstat (limited to 'src/main/java/org/apache/commons/math3/random/UnitSphereRandomVectorGenerator.java')
-rw-r--r-- | src/main/java/org/apache/commons/math3/random/UnitSphereRandomVectorGenerator.java | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/random/UnitSphereRandomVectorGenerator.java b/src/main/java/org/apache/commons/math3/random/UnitSphereRandomVectorGenerator.java new file mode 100644 index 0000000..ddcaa97 --- /dev/null +++ b/src/main/java/org/apache/commons/math3/random/UnitSphereRandomVectorGenerator.java @@ -0,0 +1,74 @@ +/* + * 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; + } +} |