Ben a écrit :
> I'm trying to take a rational map on P^1 (i.e. f(x,y) = [deg 2 poly,
> deg 2 poly] and conjugate, but I can't seem to get sage to cooperate.
>
> I would like to take a generic degree 2 map on P^1, and conjugate by
> an element of PGL_2. For example, I can do
>
> R.<X,Y> = PolynomialRing(QQ,2)
> def f(A,B):
> return A[0]*B[0]^2 + A[1]*B[1]^2 + A[2]*B[0]*B[1],A[3]*B[0]^2 +
> A[4]*B[1]^2 + A[5]*B[0]*B[1]
>
> x1,x2,x3,y1,y2,y3=var('x1,x2,x3,y1,y2,y3')
> Avar=[x1,x2,x3,y1,y2,y3]
>
> M= matrix([[0, -1],[1, -1]])
> Z=f(Avar,M*vector([R.0,R.1]))
> ZZ=M.inverse()*vector(Z)
>
> Where ZZ is now a 2-tuple where I have conjugated f by M. Now, I
> would like to extract the coefficients of the monomials (X^2,XY,Y^2)
> from each entry of ZZ, but I can't seem to get that done using
> the .coefficients() functions. I think I'm not doing a good job with
> difference between symbolic expressions, functions, and polynomials.
I think what you want is to replace the first line by
R.<X,Y> = PolynomialRing(SR, 2)
Then the elements of R will be allowed to contain symbolic variables.
--
Marc Mezzarobba
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