Qgh_deriv               g-and-h Q derivative
Qgh_log_deriv           g-and-h Q log derivative
Qgk_deriv               g-and-k Q derivative
Qgk_log_deriv           g-and-k Q log derivative
dgh                     g-and-h distribution functions
dgk                     g-and-k distribution functions
isValid                 Check validity of g-and-k or g-and-h parameters
isValid_scalar          Check validity of g-and-k or g-and-h parameters
pgh_scalar              Distribution function for the g-and-h
                        distribution
pgk_scalar              Distribution function for the g-and-k
                        distribution
z2gh                    Transform standard normal draws to g-and-h
                        draws.
z2gk                    Transform standard normal draws to g-and-k
                        draws.
