

Java example source code file (UnitSphereRandomVectorGeneratorTest.java)
The UnitSphereRandomVectorGeneratorTest.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/LICENSE2.0 * * 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; import org.junit.Assert; import org.junit.Test; public class UnitSphereRandomVectorGeneratorTest { /** * Test the distribution of points from {@link UnitSphereRandomVectorGenerator#nextVector()} * in two dimensions. */ @Test public void test2DDistribution() { RandomGenerator rg = new JDKRandomGenerator(); rg.setSeed(17399225432l); UnitSphereRandomVectorGenerator generator = new UnitSphereRandomVectorGenerator(2, rg); // In 2D, angles with a given vector should be uniformly distributed int[] angleBuckets = new int[100]; int steps = 1000000; for (int i = 0; i < steps; ++i) { final double[] v = generator.nextVector(); Assert.assertEquals(2, v.length); Assert.assertEquals(1, length(v), 1e10); // Compute angle formed with vector (1,0) // Cosine of angle is their dot product, because both are unit length // Dot product here is just the first element of the vector by construction final double angle = FastMath.acos(v[0]); final int bucket = (int) (angleBuckets.length * (angle / FastMath.PI)); ++angleBuckets[bucket]; } // Simplistic test for roughly even distribution final int expectedBucketSize = steps / angleBuckets.length; for (int bucket : angleBuckets) { Assert.assertTrue("Bucket count " + bucket + " vs expected " + expectedBucketSize, FastMath.abs(expectedBucketSize  bucket) < 350); } } /** * @return length (L2 norm) of given vector */ private static double length(double[] vector) { double total = 0; for (double d : vector) { total += d * d; } return FastMath.sqrt(total); } } Other Java examples (source code examples)Here is a short list of links related to this Java UnitSphereRandomVectorGeneratorTest.java source code file: 
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