I think you could look at the methods / code used in Maxima, already part of Sage, to see how formal power series of multiple variable expressions are computed without computing derivatives. There's also a literature on fast computation of series ( Brent, Kung and Traub -- google is your friend --) and taking derivatives is, I think, not part of this at all. Specifying the number of terms requires you to identify the situation where the leading non-zero term is -- oops -- zero. Maybe the sympy people have already duplicated this capability. Not that they have necessarily done it right. Or you could just call Maxima.
Good luck. RJF -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
