[GiNaC-list] Fwd: Performance problem with series

[Chris Dams]

Dear Frieder,

On Wed, 19 Jan 2005, Frieder Kalisch wrote:

> here is a very odd performance behaviour of ginac/series.

Okay, I had a quick look at this. There are two questions that I am
asking myself now:
(1) How should .series() perform its calculation?
(2) What should the result be like?

Ad (1): I think series expansion should most of the time not be done by
repeated differentiation. What if some large addition appears as a
subexpression? The chain rule together with expansion of the derivatives
(in the sense of .expand()) will cause expression explosion and happyness
is not going to occur.

Ad (2): I think that the expansion coefficients should be in expandend
form (again in the sense of .expand()). If the main developpers agree on
this, then you have just located a bug. The coefficients of the result of
your example look more than a bit unexpanded....

Best wishes,
Chris