Dear Jordi,
Have you found an answer for your question about 'Differentiate into a
sum' posted last month on this list?
I was looking for a solution for a similar problem.
I've found this article:
http://people.clarkson.edu/~chengweb/faculty/taylor/cache98/cache98.htm
which describes a Maple extension for the differentiation of arbitrary sums.
The code for this extension can be found at:
http://www.mirrorservice.org/sites/ftp.inf.ethz.ch/pub/software/maple/5.3/share/TDTools
Once Maxima and Maple are very similar, maybe that code could be converted to Maxima.
Unfortunately I'm not a Maxima nor Maple expert, anyone can help in this task?
Thank you in advance.
--
Rafael