#17659: make symbolic series subclass of Expression
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Reporter: rws | Owner:
Type: | Status: needs_review
enhancement | Milestone: sage-6.5
Priority: major | Resolution:
Component: | Merged in:
symbolics | Reviewers:
Keywords: | Work issues:
Authors: Ralf | Commit:
Stephan | ed003f04b1eefba775e841c0dbfaffdb66d0953a
Report Upstream: N/A | Stopgaps:
Branch: |
u/rws/17659 |
Dependencies: |
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Comment (by nbruin):
OK, I thought that `f.is_series()` would do some non-trivial logic to see
if `f` can be used as a series, but it's just exposing a flag that is held
internally somewhere. You could indeed expose that information in the type
instead, but with ducktyping, subtyping and sage's parent infrastructure
doing so might not be as convenient as it might be in systems that are
really governed by explicit types. You'd need to think if this refactoring
actually will help for further development.
Indeed, being a "series" seems a rather fickle property. It doesn't seem
to be preserved under anything:
{{{
sage: var('x,y');
sage: f=cos(y).series(y,10)
sage: g=sin(x).series(x,10)
sage: var('x,y');
sage: f=cos(y).series(y,10)
sage: g=sin(x).series(x,10)
sage: f.is_series()
True
sage: (f+f).is_series()
False
sage: (-f).is_series()
False
sage: (f+g).series(x,10)
Order(1)
}}}
The last result probably follows from interpreting the `Order(x^10)` term
in `g` as an order term in `y`, and hence equivalent to `Order(y^0)`.
--
Ticket URL: <http://trac.sagemath.org/ticket/17659#comment:8>
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