#12737: Add an `unsafe` argument to Expression.simplify_full()
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Reporter: mjo | Owner: mjo
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: symbolics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: #12650 | Stopgaps:
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Comment (by mjo):
Replying to [comment:2 nbruin]:
> It's not entirely clear to me which simplifications are "safe" and which
are not. Simplifying `x^2/x` to `x` is also not "safe" in the sense that
equality does not hold for `x=0`. In many computer algebra systems,
acceptable simplifications are not "safe" in this respect. By including a
default `unsafe=False` I'm afraid you'll be raising expectations to a
level that Sage does not attain (yet?).
It's completely heuristic: the four I chose nobody seems to have a problem
with. `simplify_radical`, on the other hand, wreaks havoc on trivial
functions and has been the cause of numerous bug reports and mailing list
discussions.
In `simplify`, after #12650, I say that a safe simplification is one "for
which we are reasonably sure that the input will be considered equivalent
to the output." That's probably the best we can do for now, and I'm
''reasonably sure'' that most people would consider `x^2/x` equivalent to
`x`.
As it stands, I think `full_simplify` ''sounds'' safe so people will
assume that anyway. This fix, while not perfect, at least improves things.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12737#comment:3>
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