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> 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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