public class Landau
extends AbstractIFunction
The function represents the Landau distribution.
This class represents a Landau distribution, as
approximated by the Moyal formula
\[ Moyal(\lambda) = \frac{\exp{-0.5(\lambda+\exp{-\lambda})}}{\sqrt{2\pi}} \]
See J.E. Moyal, Theory of ionization fluctuations, Phil. Mag. 46 (1955) 263.
Note that this analytical approximation is too low in the tail.
In order to allow for a fit, we define
\[ \lambda = \frac{x - m}{s} \]
with x the dataset variable.
From Goddard GLAST ACD team (Fortran version)