/// <summary>
/// Sample from the distribution tail (defined as having x >= __R).
/// </summary>
/// <returns>A new random sample from the Gaussian distribution tail.</returns>
private static double SampleTail(IRandomSource rng)
{
double x, y;
do
{
// Note. we use NextDoubleNonZero() because Log(0) returns -Infinity and will also tend to be a very slow execution path (when it occurs, which is rarely).
x = -Math.Log(rng.NextDoubleNonZero()) / __R;
y = -Math.Log(rng.NextDoubleNonZero());
}while(y + y < x * x);
return(__R + x);
}
