laurent_polynomial.md

CurrentModule = AbstractAlgebra
DocTestSetup = quote
    using AbstractAlgebra
end

Generic Laurent polynomials

Laurent polynomials are similar to polynomials but can have terms of negative degrees, and form a ring denoted by $R[x, x^{-1}]$ where R is the coefficient ring.

Generic Laurent polynomial types

AbstractAlgebra.jl provides a generic implementation of Laurent polynomials, built in terms of regular polynomials in the file src/generic/LaurentPoly.jl.

The type LaurentPolyWrap{T, ...} <: LaurentPolyRingElem{T} implements generic Laurent polynomials by wrapping regular polynomials: a Laurent polynomial l wraps a polynomial p and an integer n such that $l = x^{-n} * p$.

The corresponding parent type is LaurentPolyWrapRing{T, ...} <: LaurentPolyRing{T}.

Abstract types

Two abstract types LaurentPolyRingElem{T} and LaurentPolyRing{T} are defined to represent Laurent polynomials and rings thereof, parameterized on a base ring T.

Laurent polynomials ring constructor

In order to instantiate Laurent polynomials, one must first construct the parent ring:

laurent_polynomial_ring

Basic functionality

Laurent polynomials implement the ring interface, and some methods from the polynomial interface, for example:

julia> R, x = laurent_polynomial_ring(ZZ, :x)
(Univariate Laurent polynomial ring in x over integers, x)

julia> var(R)
:x

julia> symbols(R)
1-element Vector{Symbol}:
 :x

julia> number_of_variables(R)
1

julia> f = x^-2 + 2x
2*x + x^-2

julia> coeff.(f, -2:2)
5-element Vector{BigInt}:
 1
 0
 0
 2
 0

julia> set_coefficient!(f, 3, ZZ(5))
5*x^3 + 2*x + x^-2

julia> is_gen(f)
false

julia> shift_left(f,2)
5*x^5 + 2*x^3 + 1

julia> map_coefficients(x->2x, f)
10*x^3 + 4*x + 2*x^-2

julia> change_base_ring(RealField, f)
5.0*x^3 + 2.0*x + x^-2

julia> leading_coefficient(f), trailing_coefficient(f)
(5, 1)