#15348: "R.<a> =" syntactic sugar incorrect for EquationOrder and ZZ.extension
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Reporter: emassop | Owner:
Type: defect | Status: new
Priority: minor | Milestone:
Component: number fields | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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After typing
{{{
sage: f = x^2+1
sage: R.<i> = ZZ.extension(f)
}}}
I expect variable {{{i}}} to be the element of {{{R}}} named {{{'i'}}}.
However, it is not. It is the element 1.
This is due to the generators of an order in Sage being its //module//
generators (as noted by {{{EquationOrder?}}}):
{{{
sage: R.gens()
[1, i]
sage: preparse("R.<i> = ZZ.extension(f)")
"R = ZZ.extension(f, names=('i',)); (i,) = R._first_ngens(1)"
}}}
I see three ways of fixing this:
1) redefine {{{AbsoluteOrder.gens()}}},
2) make {{{preparse(...)}}} output {{{i = R._element_constructor('i')}}}
instead of {{{(i,) = R._first_ngens(1)}}},
3) disallow {{{R.<i> = }}} for {{{EquationOrder}}}.
Way (1) might make previously good code produce wrong results, so it is
not a good idea.
For way (2), {{{_element_constructor}}} should have uniquitious support,
about which I am unsure. I think way (3) might be achieved by renaming the
argument {{{names}}} of {{{EquationOrder}}} to {{{field_names}}} or
somesuch. (For the short term I think {{{names}}} should still be
accepted, but with a warning.)
--
Ticket URL: <http://trac.sagemath.org/ticket/15348>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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