#5917: Failing conversions for multipolynomial rings over fraction fields
---------------------------------+------------------------------------------
Reporter: SimonKing | Owner: malb
Type: defect | Status: new
Priority: critical | Milestone: sage-4.0
Component: commutative algebra | Keywords: polynomial ring fraction field
conversion
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The following is with sage-3.4.1 on sage.math:
Setting:
{{{
sage: F1 = FractionField(PolynomialRing(QQ,'a'))
sage: R11 = F1['x']
sage: R12 = F1['x','y']
sage: F2 = FractionField(PolynomialRing(QQ,['a','b']))
sage: R21 = F2['x']
sage: R22 = F2['x','y']
}}}
Here I try various conversions, some of them go boom:
{{{
sage: F1('a')
a
sage: F2('a')
a
sage: R11('a')
a
sage: R12('a')
Traceback (most recent call last):
...
TypeError: unable to convert string
sage: R21('a')
a
sage: R22('a')
Traceback (most recent call last):
...
TypeError: unable to convert string
sage: R11(F1('a'))
a
sage: R12(F1('a'))
a
sage: R21(F2('a'))
a
sage: R22(F2('a'))
a
sage: F1(R11(F1('a')))
a
sage: F1(R12(F1('a')))
Traceback (most recent call last)
...
TypeError: unable to convert a to a rational
sage: F2(R21(F2('a')))
a
sage: F2(R22(F2('a')))
Traceback (most recent call last)
...
TypeError:
}}}
Note that in the last example there is no error message. So, it seems to
be different from the previous error ("unable to convert a to a rational")
'''__Conclusion:__'''
* Conversion from string to fraction field is OK both with one and two
variables.
* Conversion from a string to a univariate polynomial ring over a
fraction field works, but fails for multivariate polynomial rings over a
fraction field.
* Conversion from a fraction field to a polynomial ring over this
fraction field works both uni- and multivariately.
* Conversion of a ''scalar'' element of a ''multivariate'' polynomial
ring over a fraction field into that fraction field fails. The univariate
case seems ok. The error seems to depend on the number of variables of the
fraction field.
Since conversion is something very elementary, I consider it a critical
bug if it does not work (but not a blocker since it doesn't affect
coercion).
Probably it is too late for sage-3.4.2, so, I give it the Milestone 4.0.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5917>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
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