The stable density function in these routines is calculated using the fast Fourier transform. The Nolan 0-parameterization is used.
is the distribution shape parameter, a positive value less than or equal to 2. For
the result is the normal distribution.
is the tail exponent of the distribution: lower values give fatter tails.
is the skewness parameter in the range (-1, 1).
is the scale parameter.
is the location parameter.
The routine used can result in numeric instabilities for small values of
and so a reduced range is used.
