Alphabeta Math

Symmetric Polynomials and the Fundamental Theorem of Symmetric Functions

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✓ 21 results · all verified · 12 also independently AI-judged
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1 · Prerequisites
2 · Logical flowchart

3 · Items

Definition

Symmetric polynomials as the invariants of variable permutations

Proposition

The symmetric polynomials form a subring

Definition

The elementary symmetric polynomials e₀,e₁,…,eₙ

Theorem

Vieta expansion: ∏ᵢ₌₁ⁿ(t-xᵢ)=∑ₖ₌₀ⁿ(-1)ᵏ eₖ tⁿ⁻ᵏ

Corollary

Vieta's formulas identify the coefficients of a split monic polynomial with elementary symmetric functions of its roots

Definition

Monomial symmetric polynomials indexed by partitions

Theorem

Monomial symmetric polynomials form an R-basis of the symmetric-polynomial ring

Definition

Lexicographic order on exponent tuples and the multidegree of a nonzero polynomial

Lemma

The leading multidegree of a symmetric polynomial is weakly decreasing

Lemma

The leading multidegree of e₁^b₁⋯ eₙ^bₙ is (b₁+⋯+bₙ,b₂+⋯+bₙ,…,bₙ) with coefficient one

Theorem

Every symmetric polynomial over a commutative ring is a polynomial in the elementary symmetric polynomials

Theorem

The elementary symmetric polynomials are algebraically independent over the coefficient ring

Theorem

Fundamental theorem of symmetric polynomials: unique expression as a polynomial in e₁,…,eₙ

Corollary

A symmetric polynomial in the roots of a monic polynomial is a polynomial in its coefficients and lies in the base ring

Definition

Power sums pₖ and complete homogeneous symmetric polynomials hₖ

Proposition

The generating-series identity E(-t)H(t)=1

Corollary

The complete homogeneous symmetric polynomials h₁,…,hₙ freely generate the symmetric-polynomial ring

Theorem

Newton's identities: k eₖ=∑ᵢ₌₁ᵏ(-1)ⁱ⁻¹eₖ₋ᵢpᵢ

Corollary

If n! is invertible, then p₁,…,pₙ freely generate the symmetric-polynomial ring

Definition

The Vandermonde polynomial Δₙ=∏_i<j(xᵢ-xⱼ)

Proposition

The square of the Vandermonde polynomial is symmetric

Definition

The discriminant of a monic polynomial as the coefficient expression of Δₙ²

Theorem

The discriminant is ∏_i<j(αᵢ-αⱼ)² and vanishes exactly when a monic polynomial has a repeated root

Definition

The monic resultant Res(f,g) from the symmetric coefficient expression of ∏ᵢ g(xᵢ)

Theorem

For monic f, Res(f,g)=∏ᵢ g(αᵢ) and it vanishes exactly when f and g have a common root

Theorem

For monic f,g of degrees n,m splitting in a common extension, Res(f,g)=∏ᵢ₌₁ⁿ∏ⱼ₌₁ᵐ(αᵢ-βⱼ)

Corollary

For monic f,g of degrees n,m, Res(f,g)=(-1)ᵐⁿRes(g,f)

Corollary

For monic f, if g-g₁=qf, then Res(f,g)=Res(f,g₁)

Corollary

For monic f of degree n, Res(f,f')=(-1)^n(n-1)/2Disc(f)

Sources