#12353: wrong comparison between RealIntervalField and RealField
--------------------------------+-------------------------------------------
Reporter: zimmerma | Owner: AlexGhitza
Type: defect | Status: new
Priority: blocker | Milestone: sage-5.0
Component: basic arithmetic | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Changes (by zimmerma):
* cc: was (added)
Old description:
> consider the following:
> {{{
> sage: RealIntervalField(53)(-1) > RR(1)
> False
> sage: RealIntervalField(54)(-1) > RR(1)
> True
> }}}
> The second answer is clearly wrong.
>
> The problem seems to be the following: the {{{_richcmp}}} function
> from {{{structure/element.pyx}}} is called. With precision 54, the
> call to {{{coercion_model.canonical_coercion}}} fails, then we have
> {{{r=1}}}, the two tests around line 853 fail, and the returned value is
> {{{_rich_to_bool(op, r)}}} which does not depend on {{{left}}} and
> {{{right}}}!
>
> Paul
New description:
on some machines we get the following:
{{{
sage: RealIntervalField(53)(-1) > RR(1)
False
sage: RealIntervalField(54)(-1) > RR(1)
True
}}}
The second answer {{{True}}} is clearly wrong.
If your machine gets the correct answer {{{False}}} in both cases, then it
most probably gives:
{{{
sage: RealIntervalField(54)(1) > RR(-1)
True
sage: RealIntervalField(54)(1) > RR(-1)
False
}}}
where the second answer {{{False}}} is wrong.
--
Comment:
after some investigation, the function {{{_richcmp}}} in
{{{structure/element.pyx}}}
computes {{{r = cmp(type(left), type(right))}}}, which gives {{{r=-1}}} on
sage.math,
and {{{r=1}}} on my workstation (both with Sage 4.8).
Note that the *types* only are compared, thus by swapping the values I can
produce a
bug on sage.math too:
{{{
sage: RealIntervalField(54)(1) > RR(-1)
False
}}}
Something is badly wrong by comparing the types, not the values. Here we
need help from someone more fluent in the Sage internals.
Paul
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12353#comment:4>
Sage <http://www.sagemath.org>
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