[Rd] Extending deriv3()

[Thomas Yee]

Hello,

I was wondering if the functions deriv3(), deriv() etc. could be extended
to handle psigamma() and its special cases (digamma(), trigamma()
etc.). From the error message it seems that 'psigamma' needs to be
added to the derivatives table.
This might be easy since psigamma() has a deriv argument.

Additionally, this error message is also obtained when requesting for
the Hessian of the gamma and lgamma functions:

d3 = deriv(~  gamma(y), namev="y", hessian= TRUE)
d3 = deriv(~ lgamma(y), namev="y", hessian= TRUE)

Another class of special functions worth adding are the Bessel functions.

Thanks

Thomas