#18092: evaluating symbolic expressions (without conversion to SR, i.e.,
staying in
ring of values)
-------------------------+-------------------------------------------------
Reporter: | Owner:
dkrenn | Status: needs_info
Type: | Milestone: sage-6.6
enhancement | Resolution:
Priority: major | Merged in:
Component: | Reviewers:
symbolics | Work issues:
Keywords: sd66 | Commit:
Authors: | 7e0be7f3a76c98d5ec3e5250947aec814467048b
Daniel Krenn | Stopgaps:
Report Upstream: N/A |
Branch: |
u/dkrenn/SR/eval |
Dependencies: |
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Comment (by nbruin):
The general idea is that the result of arithmetic only depends on the
parents of the input data, not on the values of the input data (because
the idea is that these things implement maps, which have domains and
codomains). When you evaluate a SR element at a non-symbolic value, you
don't know if the result can live in the parent of the original result
(e.g., `(sin(x)+y).subs(y=1)`).
The appropriate solution is probably to first *convert* your symbolic
expression to a parent where the parent is the desired thing, e.g.
{{{
sage: f = SR(1+x)
sage: R.<t>= ZZ[[]]
sage: P=R['x']
sage: P(f)(x=t^2+O(t^3))
}}}
This also has other advantages: in principle, when you do this with RIF,
you might end up with an evaluation routine that takes into account that
the coefficients are not exact and hence it could choose some more stable
way of doing the evaluation (I think that's hypothetical--likely no such
effort is made right now, but it could).
--
Ticket URL: <http://trac.sagemath.org/ticket/18092#comment:14>
Sage <http://www.sagemath.org>
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