52 lines
1.6 KiB
C#
52 lines
1.6 KiB
C#
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using System;
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namespace NLangDetect.Core.Extensions
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{
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public static class RandomExtensions
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{
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private const double _Epsilon = 2.22044604925031E-15;
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private static readonly object _mutex = new object();
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private static double _nextNextGaussian;
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private static bool _hasNextNextGaussian;
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/// <summary>
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/// Returns the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence.
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/// The general contract of nextGaussian is that one double value, chosen from (approximately) the usual normal distribution with mean 0.0 and standard deviation 1.0, is pseudorandomly generated and returned.
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/// </summary>
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/// <remarks>
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/// Taken from: http://download.oracle.com/javase/6/docs/api/java/util/Random.html (nextGaussian())
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/// </remarks>
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public static double NextGaussian(this Random random)
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{
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lock (_mutex)
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{
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if (_hasNextNextGaussian)
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{
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_hasNextNextGaussian = false;
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return _nextNextGaussian;
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}
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double v1, v2, s;
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do
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{
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v1 = 2.0 * random.NextDouble() - 1.0; // between -1.0 and 1.0
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v2 = 2.0 * random.NextDouble() - 1.0; // between -1.0 and 1.0
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s = v1 * v1 + v2 * v2;
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}
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while (s >= 1.0 || Math.Abs(s - 0.0) < _Epsilon);
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double multiplier = Math.Sqrt(-2.0 * Math.Log(s) / s);
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_nextNextGaussian = v2 * multiplier;
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_hasNextNextGaussian = true;
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return v1 * multiplier;
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}
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}
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}
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}
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