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commons-math-2.1 added
author dwinter
date Tue, 04 Jan 2011 10:02:07 +0100
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<FONT color="green">001</FONT>    /*<a name="line.1"></a>
<FONT color="green">002</FONT>     * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a>
<FONT color="green">003</FONT>     * contributor license agreements.  See the NOTICE file distributed with<a name="line.3"></a>
<FONT color="green">004</FONT>     * this work for additional information regarding copyright ownership.<a name="line.4"></a>
<FONT color="green">005</FONT>     * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a>
<FONT color="green">006</FONT>     * (the "License"); you may not use this file except in compliance with<a name="line.6"></a>
<FONT color="green">007</FONT>     * the License.  You may obtain a copy of the License at<a name="line.7"></a>
<FONT color="green">008</FONT>     *<a name="line.8"></a>
<FONT color="green">009</FONT>     *      http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a>
<FONT color="green">010</FONT>     *<a name="line.10"></a>
<FONT color="green">011</FONT>     * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a>
<FONT color="green">012</FONT>     * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a>
<FONT color="green">013</FONT>     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a>
<FONT color="green">014</FONT>     * See the License for the specific language governing permissions and<a name="line.14"></a>
<FONT color="green">015</FONT>     * limitations under the License.<a name="line.15"></a>
<FONT color="green">016</FONT>     */<a name="line.16"></a>
<FONT color="green">017</FONT>    <a name="line.17"></a>
<FONT color="green">018</FONT>    package org.apache.commons.math.random;<a name="line.18"></a>
<FONT color="green">019</FONT>    <a name="line.19"></a>
<FONT color="green">020</FONT>    <a name="line.20"></a>
<FONT color="green">021</FONT>    /**<a name="line.21"></a>
<FONT color="green">022</FONT>     * Generate random vectors isotropically located on the surface of a sphere.<a name="line.22"></a>
<FONT color="green">023</FONT>     *<a name="line.23"></a>
<FONT color="green">024</FONT>     * @since 2.1<a name="line.24"></a>
<FONT color="green">025</FONT>     * @version $Revision: 925812 $ $Date: 2010-03-21 11:49:31 -0400 (Sun, 21 Mar 2010) $<a name="line.25"></a>
<FONT color="green">026</FONT>     */<a name="line.26"></a>
<FONT color="green">027</FONT>    <a name="line.27"></a>
<FONT color="green">028</FONT>    public class UnitSphereRandomVectorGenerator<a name="line.28"></a>
<FONT color="green">029</FONT>        implements RandomVectorGenerator {<a name="line.29"></a>
<FONT color="green">030</FONT>        /**<a name="line.30"></a>
<FONT color="green">031</FONT>         * RNG used for generating the individual components of the vectors.<a name="line.31"></a>
<FONT color="green">032</FONT>         */<a name="line.32"></a>
<FONT color="green">033</FONT>        private final RandomGenerator rand;<a name="line.33"></a>
<FONT color="green">034</FONT>        /**<a name="line.34"></a>
<FONT color="green">035</FONT>         * Space dimension.<a name="line.35"></a>
<FONT color="green">036</FONT>         */<a name="line.36"></a>
<FONT color="green">037</FONT>        private final int dimension;<a name="line.37"></a>
<FONT color="green">038</FONT>    <a name="line.38"></a>
<FONT color="green">039</FONT>        /**<a name="line.39"></a>
<FONT color="green">040</FONT>         * @param dimension Space dimension.<a name="line.40"></a>
<FONT color="green">041</FONT>         * @param rand RNG for the individual components of the vectors.<a name="line.41"></a>
<FONT color="green">042</FONT>         */<a name="line.42"></a>
<FONT color="green">043</FONT>        public UnitSphereRandomVectorGenerator(final int dimension,<a name="line.43"></a>
<FONT color="green">044</FONT>                                               final RandomGenerator rand) {<a name="line.44"></a>
<FONT color="green">045</FONT>            this.dimension = dimension;<a name="line.45"></a>
<FONT color="green">046</FONT>            this.rand = rand;<a name="line.46"></a>
<FONT color="green">047</FONT>        }<a name="line.47"></a>
<FONT color="green">048</FONT>        /**<a name="line.48"></a>
<FONT color="green">049</FONT>         * Create an object that will use a default RNG ({@link MersenneTwister}),<a name="line.49"></a>
<FONT color="green">050</FONT>         * in order to generate the individual components.<a name="line.50"></a>
<FONT color="green">051</FONT>         *<a name="line.51"></a>
<FONT color="green">052</FONT>         * @param dimension Space dimension.<a name="line.52"></a>
<FONT color="green">053</FONT>         */<a name="line.53"></a>
<FONT color="green">054</FONT>        public UnitSphereRandomVectorGenerator(final int dimension) {<a name="line.54"></a>
<FONT color="green">055</FONT>            this(dimension, new MersenneTwister());<a name="line.55"></a>
<FONT color="green">056</FONT>        }<a name="line.56"></a>
<FONT color="green">057</FONT>    <a name="line.57"></a>
<FONT color="green">058</FONT>        /** {@inheritDoc} */<a name="line.58"></a>
<FONT color="green">059</FONT>        public double[] nextVector() {<a name="line.59"></a>
<FONT color="green">060</FONT>    <a name="line.60"></a>
<FONT color="green">061</FONT>            final double[] v = new double[dimension];<a name="line.61"></a>
<FONT color="green">062</FONT>    <a name="line.62"></a>
<FONT color="green">063</FONT>            double normSq;<a name="line.63"></a>
<FONT color="green">064</FONT>            do {<a name="line.64"></a>
<FONT color="green">065</FONT>                normSq = 0;<a name="line.65"></a>
<FONT color="green">066</FONT>                for (int i = 0; i &lt; dimension; i++) {<a name="line.66"></a>
<FONT color="green">067</FONT>                    final double comp = 2 * rand.nextDouble() - 1;<a name="line.67"></a>
<FONT color="green">068</FONT>                    v[i] = comp;<a name="line.68"></a>
<FONT color="green">069</FONT>                    normSq += comp * comp;<a name="line.69"></a>
<FONT color="green">070</FONT>                }<a name="line.70"></a>
<FONT color="green">071</FONT>            } while (normSq &gt; 1);<a name="line.71"></a>
<FONT color="green">072</FONT>    <a name="line.72"></a>
<FONT color="green">073</FONT>            final double f = 1 / Math.sqrt(normSq);<a name="line.73"></a>
<FONT color="green">074</FONT>            for (int i = 0; i &lt; dimension; i++) {<a name="line.74"></a>
<FONT color="green">075</FONT>                v[i] *= f;<a name="line.75"></a>
<FONT color="green">076</FONT>            }<a name="line.76"></a>
<FONT color="green">077</FONT>    <a name="line.77"></a>
<FONT color="green">078</FONT>            return v;<a name="line.78"></a>
<FONT color="green">079</FONT>    <a name="line.79"></a>
<FONT color="green">080</FONT>        }<a name="line.80"></a>
<FONT color="green">081</FONT>    <a name="line.81"></a>
<FONT color="green">082</FONT>    }<a name="line.82"></a>




























































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