52 lines
1.6 KiB
C#
52 lines
1.6 KiB
C#
using System;
|
|
|
|
namespace NLangDetect.Core.Extensions
|
|
{
|
|
public static class RandomExtensions
|
|
{
|
|
private const double _Epsilon = 2.22044604925031E-15;
|
|
|
|
private static readonly object _mutex = new object();
|
|
|
|
private static double _nextNextGaussian;
|
|
private static bool _hasNextNextGaussian;
|
|
|
|
/// <summary>
|
|
/// 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.
|
|
/// 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.
|
|
/// </summary>
|
|
/// <remarks>
|
|
/// Taken from: http://download.oracle.com/javase/6/docs/api/java/util/Random.html (nextGaussian())
|
|
/// </remarks>
|
|
public static double NextGaussian(this Random random)
|
|
{
|
|
lock (_mutex)
|
|
{
|
|
if (_hasNextNextGaussian)
|
|
{
|
|
_hasNextNextGaussian = false;
|
|
|
|
return _nextNextGaussian;
|
|
}
|
|
|
|
double v1, v2, s;
|
|
|
|
do
|
|
{
|
|
v1 = 2.0 * random.NextDouble() - 1.0; // between -1.0 and 1.0
|
|
v2 = 2.0 * random.NextDouble() - 1.0; // between -1.0 and 1.0
|
|
s = v1 * v1 + v2 * v2;
|
|
}
|
|
while (s >= 1.0 || Math.Abs(s - 0.0) < _Epsilon);
|
|
|
|
double multiplier = Math.Sqrt(-2.0 * Math.Log(s) / s);
|
|
|
|
_nextNextGaussian = v2 * multiplier;
|
|
_hasNextNextGaussian = true;
|
|
|
|
return v1 * multiplier;
|
|
}
|
|
}
|
|
}
|
|
}
|