/// <summary>
/// Computes the logarithm of the Beta function.
/// </summary>
/// <param name="a">The first parameter, which must be positive.</param>
/// <param name="b">The second parameter, which must be positive.</param>
/// <returns>The value of ln(B(a,b)).</returns>
/// <remarks>
/// <para>This function accurately computes ln(B(a,b)) even for values of a and b for which B(a,b) is
/// too small or large to be represented by a double.</para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="a"/> or <paramref name="b"/> is negative or zero.</exception>
/// <seealso cref="Beta(System.Double,System.Double)"/>
public static double LogBeta(double a, double b)
{
if ((a > 16.0) && (b > 16.0))
{
return(Stirling.LogBeta(a, b));
}
else if (a < 0.0)
{
throw new ArgumentOutOfRangeException(nameof(a));
}
else if (b < 0.0)
{
throw new ArgumentOutOfRangeException(nameof(b));
}
else if (Double.IsNaN(a) || Double.IsNaN(b))
{
return(Double.NaN);
}
else if (a == 0.0 || b == 0.0)
{
return(Double.PositiveInfinity);
}
else
{
return(Lanczos.LogBeta(a, b));
}
}
/// <summary>
/// Computes the lograrithm of the Beta function.
/// </summary>
/// <param name="a">The first parameter, which must be positive.</param>
/// <param name="b">The second parameter, which must be positive.</param>
/// <returns>The value of ln(B(a,b)).</returns>
/// <remarks>
/// <para>This function accurately computes ln(B(a,b)) even for values of a and b for which B(a,b) is
/// too small or large to be represented by a double.</para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="a"/> or <paramref name="b"/> is non-positive.</exception>
/// <seealso cref="Beta(System.Double,System.Double)"/>
public static double LogBeta(double a, double b)
{
if (a <= 0.0)
{
throw new ArgumentOutOfRangeException("a");
}
if (b <= 0.0)
{
throw new ArgumentOutOfRangeException("b");
}
if ((a > 16.0) && (b > 16.0))
{
return(Stirling.LogBeta(a, b));
}
else
{
return(Lanczos.LogBeta(a, b));
}
}
