On Feb 18, 10:31 am, John Cremona <john.crem...@gmail.com> wrote:
> On Feb 18, 9:15 am, zieglerk <konstantin.zieg...@gmail.com> 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.
Thanks for the hint to use f[2] or even g[1,2] for multivariate
polynomials.
> > 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.
That's irritating. I am using the binaries for OpenSUSE 11.1 and just
to make sure, I downloaded them again, checked the MD5-sum, but still
with the same results/errors as described.
Maybe, I'll just wait for the next release. Or see if I can reproduce
the errors on the online notebook. But I have to go for now.
Thanks, again,
Konstantin
> > 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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