On Wed, May 6, 2009 at 2:20 AM, Yann <yannlaiglecha...@gmail.com> wrote:
>
> Just for the record,
> isn't the following a bug?
>
> sage: p=RealIntervalField(4)(3.1)
> sage: p.str(style='brackets')
> '[3.00 .. 3.25]'
> sage: p
> 4.?
It's a deliberate design decision. To quote from real_mpfi.pyx:
When there are two
possible results of equal precision and with the same error width,
then we pick the one which is farther from zero. (For instance,
RIF(0, 123) with two error digits could print as 61.?62 or 62.?62.
We prefer the latter because it makes it clear that the interval is
known not to be negative.)
In other words,
sage: RealIntervalField(4)(0, 1)
1.?
prints as the interval [0 .. 2], rather than [-1 .. 1], because IMHO
it is useful to be able to know that an interval is nonnegative; and
we do this by always picking the result farther from zero whenever
there are two possible "correct" printings. (Note that 3.? and 4.?
would both include the interval [3.00 .. 3.25], so they are both
correct in that sense.)
It would be possible to use a different rule for choosing between two
correct answers, but I like the current one.
Carl
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