[GiNaC-list] Evaluating multiple polylogarithms using GiNaC

[Peter Banks]

Hi there,

I am having a bit of trouble evaluating some multiple polylogarithms
using the latest version of GiNaC. GiNaC is giving me a different
response depending on whether I input the values as fractions or
decimals.

Specifically, I'm trying to find a floating point representation for
Li({1,1,2}, {1+1/2*I, 1, 3/5 - 4/5*I}). I've tried this by running (in
ginsh):

evalf(Li({1,1,2}, {1+1/2*I, 1, 3/5 - 4/5*I}));

but this seems to hang (I've run it for over 12 hours with no result).

On the other hand, running

evalf(Li({1,1,2}, {1+0.5*I, 1, 3/5 - 4/5*I}));

gives an answer almost immediately.

I've tried this using a C++ program (see attached) which behaves in
the same way: no result using the fraction but an answer with no
issues using a decimal number.

These calculations have been run using GiNaC 1.7.0 (stable & from git)
on ArchLinux.

Please let me know if there is anything I should try.

Peter

PS: I tried sending this email from a different address but it said it
was greylist - I apologise if I've sent this twice.
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