On 11/21/23 20:10, Waldek Hebisch wrote:
If current limit can handle result from integrate, then the limit
can expand the rootSum just like integrate does. Not an improvement,
but also not a step back, right?
Well, we want to handle more cases. But there is also problem
of incorrect results. Old limit code has a few fundamental
problems, basically parts of it work on principle "this
usually produces correct result". But sometimes we get
wrong results. Handling of symbolic roots is in this category.
In MRVLIM I tried to avoid such things. There is still possiblity
that MRVLIM gets something which breaks assumptions from
other parts of FriCAS (or from the user), but I do not want
to deliberatly include unsound code in MRVLIM. To put it
differently, if we allow the same liberty for new code as
for old code, then we will never get rid of unsound parts.
You may ask why unsound parts were included at all? Well,
one thing is research: in research you concentrate on
one part and take other as given, that is the only sane
way of doing research. But when it comes to implementation
it may happen that part treated "as given" is in fact
unavailable. Then you need to substitute something
which works well enough to test the new part. There
is also competitive pressure: if competitor uses
unsound method there is strong pressure to "do something"
which frequently boils down to using the same unsound
method. But IMO there is no compeling reason _now_
to include unsound methods in MRVLIM.
Can you give a concrete example that limit fails to do
rootSum? Also, is limit on rootSum generally solvable?
- Qian
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