#16127: Fix comparison of PARI objects
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Reporter: pbruin | Owner:
Type: defect | Status: needs_info
Priority: critical | Milestone: sage-6.4
Component: interfaces | Resolution:
Keywords: pari comparison | Merged in:
Authors: Peter Bruin | Reviewers: Jeroen Demeyer
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jdemeyer/ticket/16127 | 12fbcad65c6438fe0495c3b2424468f24b49a9ee
Dependencies: | Stopgaps:
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Comment (by pbruin):
Replying to [comment:22 jdemeyer]:
> Replying to [comment:18 pbruin]:
> > in my opinion asking whether `a <= b` only makes sense if `a` and `b`
are in some partially ordered set (like the real numbers with plus and
minus infinity).
> In that case, we should give an exception when asking for `a <= b`. I
think returning False is more wrong than returning True when the objects
are equal.
OK, I think raising an error is conceptually and technically the right
solution. Earlier I wrongly convinced myself that comparison operators
should never fail, but since they can, it makes sense to keep the
behaviour of `gen` objects under comparison as close as possible to what
PARI does, if only for efficiency reasons.
It turns out that there are only a few places where Sage tries to sort
unordered PARI objects (polynomials, in fact). We can basically use
`list.sort(cmp=cmp)` to force the use of `__cmp__()` instead of the rich
comparison operators. In two cases (`enumerate_totallyreal_fields_*`) it
is a bit more tricky, but after the necessary modifications the code
actually becomes cleaner in my opinion (and not measurably slower).
Now testing if this approach works, and if it keeps working after
experimentally replacing string comparison by PARI's `cmp_universal()`.
--
Ticket URL: <http://trac.sagemath.org/ticket/16127#comment:23>
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