I've been thinking about this same topic a lot recently (partially due to a question about a G-function form of tanh), and it seems like the more generalized G-function you mentioned, Ondrej, is probably necessary at some point. There doesn't seem to be a whole lot of literature on these bivariate G-functions, but, if you extend the scope to H-functions and bivariate hypergeometric functions (e.g. Horn, Appell), there are at least enough useful identities to consider implementing. Here's one interesting identity involving that generalized G-function and the Appell: http://functions.wolfram.com/07.34.16.0003.01.
Also, there are some explicit series expansions for H-functions might help: http://arxiv.org/abs/math/9803163. On Monday, February 1, 2016 at 2:28:18 PM UTC-6, Ondřej Čertík wrote: > > On Mon, Feb 1, 2016 at 1:26 PM, Ondřej Čertík <ondrej...@gmail.com > <javascript:>> wrote: > [...] > > right, that cos^2(x) is not a (single) hypergeometric series. Which is > > fine, there is problem. > > -> there is no problem. > > Ondrej > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/3e750003-cf00-4e6e-8e1c-c032fc7dc037%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
