On May 7, 2009, at 2:15 PM, John Cremona wrote:
> It is a documented feature -- look at the docstring which says
>
> def coefficient(self, degrees):
> """
> Return the coefficient of the variables with the degrees
> specified in the python dictionary \code{degrees}.
> Mathematically,
> this is the coefficient in the base ring adjoined by the
> variables
> of this ring not listed in \code{degrees}. However, the
> result
> has the same parent as this polynomial.
>
> This function contrasts with the function \code
> {monomial_coefficient}
> which returns the coefficient in the base ring of a monomial.
>
> I do agree that it is a strange design, and would prefer
> f.coefficient() to return an element of the base ring.
I agree. I think it's to support stuff like
sage: sage: K.<x,y,z>=QQ[]
sage: f = (x+1)^5*(y+1)^3
sage: f.coefficient(x^2*y^0)
10*y^3 + 30*y^2 + 30*y + 10
which is also an annoying interface to work with.
> 2009/5/7 Soroosh Yazdani <[email protected]>:
>> Hi,
>>
>> this might be a design decision, so I haven't filed a bug report
>> for it yet.
>> However, it seems that coefficient is returning the wrong type
>> when it's
>> called on multinomials. Here is an example code:
>>
>> sage: K.<x,y,z>=QQ[]
>> sage: f = x^3+y^3+z^3
>> sage: f.coefficient([3,0,0]).parent()
>> Multivariate Polynomial Ring in x, y, z over Rational Field
>>
>> It makes more sense for the above return value to be the Rational
>> Field.
>> Similarly, f.coefficient([3,None,None]).parent(), should probably
>> return
>> "Multivariate Polynomial Ring in x, z over Rational Field".
>>
>> Should I file a bug for this?
>> Soroosh
>>
>>
>>>
>>
>
> >
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