[Rd] "Math" group generics for S4, and a bug

  >> Duncan Murdoch

      DM> You might have better luck with

      DM> log1p(tasa)

    MM> {very good point, thank you, Duncan!}

       DM> if the authors of the Matrix package have written a
       DM> method for log1p(); if not, you'll probably have to do
       DM> it yourself.

    MM> They have not yet.

    MM> Note however that this - and expm1() - would
    MM> automagically work for sparse matrices if these two
    MM> functions were part of the "Math" S4 group generic.

    MM> I'd say that there's only historical reason for them

I'm now going to propose ...

As I found, expm1() and log1p() already *HAVE BEEN* in the S3 "Math" group generic

   ``automagically by implementation''.
Just the documentation for this fact has been missing.

Hence, I've added that doc (uncommitted) and I'm about to add them to the S4 Math group as well. When doing so, I'd like to add few more functions to make S3 and S4 "Math" a bit more compatible : Consequently, I'm proposing to add the following functions to the S4 Math group generic :

• log1p, expm1
• cummax, cummin {S3 has them; cumprod(), cumsum() are already}
• digamma, trigamma {S3 has them; gamma(), lgamma() are already}

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