ASKSAGE: Sage Q&A Forum - Latest question feedhttp://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Sun, 27 Dec 2015 02:33:06 -0600Computations with complex algebraic numbers?http://ask.sagemath.org/question/31857/computations-with-complex-algebraic-numbers/I am trying to perform some Newton-type computations: `z-p(z)/p'(z)` where `p(z)` is a polynomial over the field of algebraic numbers.
For example, this shows the sort of thing I'm trying to do:
p = (z^2+1)*(z^2+4)
q = p/(z-I)
pd = diff(p,z)
qd = diff(q,z)
sol = solve(qd=0,solution_dict='true')
a0 = sol[0][z]
b0 = a0-p.subs(z=a0)/pd.subs(z=a0)
However, this doesn't work because the expression `z-I` is not recognized as a factor of `p`. So I might try defining
`p` as a polynomial over the field `QQbar`:
R.<z> = PolynomialRing(QQbar)
p = (z^2+1)*(z^2+4)
q = p.quo_rem(z-I)[0]
pd = p.differentiate(z)
qd = q.differentiate(z)
The trouble now is that I can only seem to solve `qd` over `CC`: that is, in numerical form. Both the commands
qd.roots()
qd.factor()
produce numerical roots; I can't use `solve` on `qd` to obtain closed-form expressions for the roots. I've also tried the first method above prefaced with `z=QQbar['z'].0` but to no avail.
Is there some way of doing this entire computation over `QQbar`, that is, with exact complex numbers instead of numerical approximations?AlasdairSun, 27 Dec 2015 02:33:06 -0600http://ask.sagemath.org/question/31857/