Number fields

Number fields

AbstractAlgebra.jl provides a very naive implementation of number fields. This allows arithmetic in algebraic number fields, which are currently modeled as $\mathbb{Q}[x]$ modulo an irreducible polynomial, i.e. as a residue field.

In fact, the definition of the number field constructor is currently given in src/generic/ResidueField.jl and no type is defined for a number field. The definition mainly exists for testing purposes. It may later be replaced by a more standard implementation. For a more fully fleshed out number field implementation (based on a very high performance C library), see Nemo.jl.

Number field constructors

In order to construct number fields in AbstractAlgebra.jl, one must first construct the field itself. This is accomplished with the following constructor.

NumberField(f::AbstractAlgebra.Generic.Poly{Rational{BigInt}}, s::AbstractString, t = "\$"; cached = true)

Given an irreducible defining polynomial $f$ in $\mathbb{Q}[x]$, return a tuple $(K, x)$ consisting of the number field defined by that polynomial and a generator. The string fields are currently ignored, but are reserved for future use.

Currently the generator of the number field prints the same way as the variable in $\mathbb{Q}[x]$.


julia> R, x = PolynomialRing(QQ, "x")
(Univariate Polynomial Ring in x over Rationals, x)

julia> K, a = NumberField(x^3 + 3x + 1, "a")
(Residue field of Univariate Polynomial Ring in x over Rationals modulo x^3 + 3*x + 1, x)

julia> f = a^2 + 2a + 7
x^2 + 2*x + 7

Basic field functionality

The number field module in AbstractAlgebra.jl implements the full Field and ResidueRing interfaces.