Re: Landau distribution

[Brian Gough <bjg at network-theory dot co dot uk>]

 > OK, now the more general issue.  Schorr's technique is fairly fast, but
 > not astoundingly precise.  In his paper he claims it's good to a few
 > significant digits in the middle of the approximation interval, but only
 > good to about 5% or so at the end of that range.  That's not exactly the
 > sort of stuff numerical analysts write home about.  However, it's fine
 > for describing many physical situations, and that's how it's typically
 > used.  The question then is GSL interested in having some distributions
 > that are "good enough" for some, but not all, purposes.  This case would
 > satisfy many physicists but few mathematicians (I think). 

If the approximation is the only game in town then it's better to use
that rather than not have a useful function.  The limitations should
just be noted in the documentation.

For special functions an error estimate is part of the computed answer
so the function can accommodate a region where the approximation is
less good.