On Feb 18, 9:15 am, zieglerk <[email protected]> wrote:
> I was pretty sure, that there was a method for polynomials to extract
> the coefficient of a certain monomial (say x^2). But the method I
> used for that before
>
> R = PolynomialRing(QQ, 'x')
> f = R.random_element(degree = 3)
> f.coeff(x^2)
>
> now returns the error
>
> AttributeError: 'Polynomial_rational_dense' object has no attribute
> 'coeff'
>
> Of course, there is always the workaround by the complete list of
> coefficients:
>
> f.coeffs()[2]
You can also use f[2] for this. But I agree that a method coeff() for
univariate polynomials would be intuitive and useful.
>
> but this certainly does not generalize to multivariate polynomials.
> The code I was using until very recently (sage 4.3.1 I guess) was like
I tried all the examples you give below in Sage-4.3.2 and they all
worked fine, and not as you report.
John Cremona
>
> S = PolynomialRing(QQ, 'x, y')
> g = S.random_element(degree = 3)
> g.coeff(x^2)
>
> and now returns
>
> AttributeError:
> 'sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular'
> object has no attribute 'coeff'
>
> Again, there seems to be a workaround using g.coefficient(), but I am
> unable handle this method even with the documentation provided, e.g.
> for
>
> g = 2*x*y^2 - 2*y^3 + x^2 + 3*y^2 - 4
>
> g.coefficient({x:0, y:0}) == g
> g.coefficient({x:1, y:2}) == g
> g.coefficient({x:2, y:2}) == g
>
> are all true?! And
>
> g.coefficient(x^2)
>
> returns the error
>
> TypeError: The input degrees must be a dictionary of variables to
> exponents.
>
> although the documentation has as an example
>
> sage: R.<x,y> = QQ[]
> sage: f=(1+y+y^2)*(1+x+x^2)
> sage: f.coefficient({x:0})
> y^2 + y + 1
> sage: f.coefficient([0,None])
> y^2 + y + 1
> sage: f.coefficient(x)
> y^2 + y + 1
>
> Am I missing something here?
>
> Thanks,
> Konstantin
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