[ESS] Extensions to the derivatives table

[Jerry Lewis]

The derivative table resides in the function D.  In S+ that table is extensible because it is written in the S language.  R is faster but less flexible, since that table is programmed in C.  It would be useful if R provided a mechanism for extending the derivative table, or barring that, provided a broader table, beginning with expm1, log1p, log2 and log10.

While the proposed additions are straight-forward, their absence complicates what otherwise could be much simpler, such as using deriv() or deriv3() to generate functions, such as an nls model.

Thanks,

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