#19568: arb balls should have the precision of the parent
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Reporter: jdemeyer | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.10
Component: interfaces | Resolution:
Keywords: | Merged in:
Authors: Jeroen Demeyer | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jdemeyer/arb_balls_should_have_the_precision_of_the_parent|
638f7f581a72056c39d013e4b46cce500176a710
Dependencies: #19152 | Stopgaps:
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Comment (by mmezzarobba):
IMO saying that “arb balls can have a precision different from their
parent” isn't the right way to think about the issue. For example,
`RealBallField(100)(1)` and `RealBallField(200)(1)` both have midpoints
whose mantissa fits on 1 bit and zero radius: what is their “precision”?
The way I view it, they have none by themselves, and having
`RealBallField`s of different precisions is just a convenient way of
specifying the precision at which the results of operations on balls
should be rounded.
I don't find the way things currently work particularly confusing, while I
think it can be useful in “advanced” use (to compute the result of a
subtraction involving cancellation, say). I should also say that real
balls won't really “have the precision of their parent” even after your
change: at the very least it will still be possible to create balls whose
midpoint's precision is less than the precision of the parent—and that's a
good thing, but I'm not sure it is less confusing than the behavior you
are trying to change.
So personally I'm certainly not going to give this ticket positive_review.
That being said, I have no strong objection either to rounding integers
etc. by default when creating new balls. It just makes things a bit less
flexible for no good reason.
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Ticket URL: <http://trac.sagemath.org/ticket/19568#comment:3>
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