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Java example source code file (UnitSphereRandomVectorGenerator.java)

This example Java source code file (UnitSphereRandomVectorGenerator.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

mersennetwister, randomgenerator, randomvectorgenerator, unitsphererandomvectorgenerator

The UnitSphereRandomVectorGenerator.java Java example source code

/*
 * 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;
    }
}

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