But even if we implement expression.laurent_polynomial(), it wouldn't
automatically allow conversion from SR to LaurentPolynomialRing, would it?
We would need to populate the conversion list somehow.
El jueves, 12 de mayo de 2016, 5:33:50 (UTC+2), Ralf Stephan escribió:
>
> Then making it Expression.laurent_polynomial() but allowing
> polynomial with ring=LaurentPolyRing as argument seems to be
> the best interface.
>
> On Wed, May 11, 2016, 22:26 Nils Bruin <nbr...@sfu.ca <javascript:>>
> wrote:
>
>> On Tuesday, May 10, 2016 at 10:55:20 PM UTC-7, Ralf Stephan wrote:
>>>
>>> On Tuesday, May 10, 2016 at 10:48:10 PM UTC+2, mmarco wrote:
>>>>
>>>> Thanks for the answer. So you propose that Expression.polynomial()
>>>> should return either a polynomial or a laurent polynomial depending on the
>>>> expression?
>>>>
>>>
>>> Depending on expression and ring argument:
>>>
>>
>>
>> I think people missed the double definition of `x`, particularly because
>> the reassignment of `x` gets hidden by doing in the RHS of an assignment.
>> To be clearer:
>>
>>
>>>
>>> sage: R = PolynomialRing(QQ,'x') #to avoid confusion about what x is
>>> sage: S = LaurentPolynomialRing(QQ, 'y')
>>> sage: var('x,y,z')
>>>
>> sage: parent((z).polynomial(QQ))
>>> Univariate Polynomial Ring in z over Rational Field
>>> sage: parent((1/z+z).polynomial(QQ))
>>> Univariate Laurent Polynomial Ring in z over Rational Field
>>>
>>
>> I would say this is an error, because 1/z+z is not a polynomial over QQ
>> in most normal senses of the word. Where would you stop? what would
>>
>> (1/(z+1) + z).polynomial(QQ)
>>
>> do? Will that return an answer in QQ[z,U]/((z+1)*U-1) ?
>>
>> I know that in symbolics you have to read off return types from
>> properties of the input, not just from its type, but I think this going a
>> little too far. "SR.polynomial(...)" should return polynomials in variables
>> that are algebraically independent over the base ring. So no laurent
>> polynomials.
>>
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