#20288: Arithmetic in QQbar mutates elements
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Reporter: jdemeyer | Owner:
Type: defect | Status: new
Priority: minor | Milestone: sage-7.2
Component: number theory | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by jdemeyer:
Old description:
> When doing arithmetic with a `QQbar` element, operations subtly mutate
> the elements which should be constant.
>
> In the example below, we see that `M^2` is displayed differently after we
> compute the rank of `M`:
> {{{
> sage: M = matrix(QQbar, 2, 2, [1, sqrt(-3), -sqrt(-3), 3])
> sage: M^2
> [ 4.000000000000000? 6.928203230275509?*I]
> [-6.928203230275509?*I 12.00000000000000?]
> sage: rank(M)
> 1
> sage: M^2
> [ 4 6.928203230275509?*I]
> [-6.928203230275509?*I 12]
> }}}
New description:
When doing arithmetic with a `QQbar` element, operations subtly mutate the
elements which should be constant.
In the example below, we see that `M^2` is displayed differently after we
compute the rank of `M`:
{{{
sage: M = matrix(QQbar, 2, 2, [1, sqrt(-3), -sqrt(-3), 3])
sage: M^2
[ 4.000000000000000? 6.928203230275509?*I]
[-6.928203230275509?*I 12.00000000000000?]
sage: rank(M)
1
sage: M^2
[ 4 6.928203230275509?*I]
[-6.928203230275509?*I 12]
}}}
One can easily see the difference in the `__dict__` of the upper right
element:
{{{
sage: M = matrix(QQbar, 2, 2, [1, sqrt(-3), -sqrt(-3), 3])
sage: M[0,1].__dict__
{'_descr': Root 1.7320508075688772935?*I of x^2 + 3,
'_value': 1.7320508075688772935?*I}
sage: rank(M)
1
sage: M[0,1].__dict__
{'_descr': -2*a + 1 where a^2 - a + 1 = 0 and a in 0.50000000000000000? -
0.866025403784439?*I,
'_value': 1.73205080756887729352744634150587236694?*I}
}}}
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Ticket URL: <http://trac.sagemath.org/ticket/20288#comment:1>
Sage <http://www.sagemath.org>
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