Theory of univariate polynomials

We show that A[X] is an R-algebra when A is an R-algebra. We promote eval₂ to an algebra hom in aeval.

instance Polynomial.algebraOfAlgebra {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] : Algebra R (Polynomial A)

Note that this instance also provides Algebra R R[X].

Equations

• Polynomial.algebraOfAlgebra = Algebra.mk (Polynomial.C.comp (algebraMap R A)) ⋯ ⋯

@[simp]

theorem Polynomial.algebraMap_apply {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (r : R) : (algebraMap R (Polynomial A)) r = Polynomial.C ((algebraMap R A) r)

@[simp]

theorem Polynomial.toFinsupp_algebraMap {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (r : R) : ((algebraMap R (Polynomial A)) r).toFinsupp = (algebraMap R (AddMonoidAlgebra A ℕ)) r

theorem Polynomial.ofFinsupp_algebraMap {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (r : R) : { toFinsupp := (algebraMap R (AddMonoidAlgebra A ℕ)) r } = (algebraMap R (Polynomial A)) r

theorem Polynomial.C_eq_algebraMap {R : Type u} [CommSemiring R] (r : R) : Polynomial.C r = (algebraMap R (Polynomial R)) r

When we have [CommSemiring R], the function C is the same as algebraMap R R[X].

(But note that C is defined when R is not necessarily commutative, in which case algebraMap is not available.)

@[simp]

theorem Polynomial.algebraMap_eq {R : Type u} [CommSemiring R] : algebraMap R (Polynomial R) = Polynomial.C

@[simp]

theorem Polynomial.CAlgHom_apply {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] : ∀ (a : A), Polynomial.CAlgHom a = Polynomial.C a

def Polynomial.CAlgHom {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] : A →ₐ[R] Polynomial A

Polynomial.C as an AlgHom.

Equations

• Polynomial.CAlgHom = { toRingHom := Polynomial.C, commutes' := ⋯ }

theorem Polynomial.algHom_ext' {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] {f : Polynomial A →ₐ[R] B} {g : Polynomial A →ₐ[R] B} (hC : f.comp Polynomial.CAlgHom = g.comp Polynomial.CAlgHom) (hX : f Polynomial.X = g Polynomial.X) : f = g

Extensionality lemma for algebra maps out of A'[X] over a smaller base ring than A'

@[simp]

theorem Polynomial.toFinsuppIsoAlg_symm_apply_toFinsupp (R : Type u) [CommSemiring R] (toFinsupp : AddMonoidAlgebra R ℕ) : ((Polynomial.toFinsuppIsoAlg R).symm toFinsupp).toFinsupp = toFinsupp

@[simp]

theorem Polynomial.toFinsuppIsoAlg_apply (R : Type u) [CommSemiring R] (self : Polynomial R) : (Polynomial.toFinsuppIsoAlg R) self = self.toFinsupp

def Polynomial.toFinsuppIsoAlg (R : Type u) [CommSemiring R] : Polynomial R ≃ₐ[R] AddMonoidAlgebra R ℕ

Algebra isomorphism between R[X] and R[ℕ]. This is just an implementation detail, but it can be useful to transfer results from Finsupp to polynomials.

Equations

• Polynomial.toFinsuppIsoAlg R = let __src := Polynomial.toFinsuppIso R; { toEquiv := __src.toEquiv, map_mul' := ⋯, map_add' := ⋯, commutes' := ⋯ }

instance Polynomial.subalgebraNontrivial {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] [Nontrivial A] : Nontrivial (Subalgebra R (Polynomial A))

Equations

• ⋯ = ⋯

@[simp]

theorem Polynomial.algHom_eval₂_algebraMap {R : Type u_3} {A : Type u_4} {B : Type u_5} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (p : Polynomial R) (f : A →ₐ[R] B) (a : A) : f (Polynomial.eval₂ (algebraMap R A) a p) = Polynomial.eval₂ (algebraMap R B) (f a) p

@[simp]

theorem Polynomial.eval₂_algebraMap_X {R : Type u_3} {A : Type u_4} [CommSemiring R] [Semiring A] [Algebra R A] (p : Polynomial R) (f : Polynomial R →ₐ[R] A) : Polynomial.eval₂ (algebraMap R A) (f Polynomial.X) p = f p

@[simp]

theorem Polynomial.ringHom_eval₂_intCastRingHom {R : Type u_3} {S : Type u_4} [Ring R] [Ring S] (p : Polynomial ℤ) (f : R →+* S) (r : R) : f (Polynomial.eval₂ (Int.castRingHom R) r p) = Polynomial.eval₂ (Int.castRingHom S) (f r) p

@[deprecated Polynomial.ringHom_eval₂_intCastRingHom]

theorem Polynomial.ringHom_eval₂_cast_int_ringHom {R : Type u_3} {S : Type u_4} [Ring R] [Ring S] (p : Polynomial ℤ) (f : R →+* S) (r : R) : f (Polynomial.eval₂ (Int.castRingHom R) r p) = Polynomial.eval₂ (Int.castRingHom S) (f r) p

Alias of Polynomial.ringHom_eval₂_intCastRingHom.

@[simp]

theorem Polynomial.eval₂_intCastRingHom_X {R : Type u_3} [Ring R] (p : Polynomial ℤ) (f : Polynomial ℤ →+* R) : Polynomial.eval₂ (Int.castRingHom R) (f Polynomial.X) p = f p

@[deprecated Polynomial.eval₂_intCastRingHom_X]

theorem Polynomial.eval₂_int_castRingHom_X {R : Type u_3} [Ring R] (p : Polynomial ℤ) (f : Polynomial ℤ →+* R) : Polynomial.eval₂ (Int.castRingHom R) (f Polynomial.X) p = f p

Alias of Polynomial.eval₂_intCastRingHom_X.

@[simp]

theorem Polynomial.eval₂AlgHom'_apply {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) (b : B) (hf : ∀ (a : A), Commute (f a) b) (p : Polynomial A) : (Polynomial.eval₂AlgHom' f b hf) p = Polynomial.eval₂ (↑f) b p

def Polynomial.eval₂AlgHom' {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) (b : B) (hf : ∀ (a : A), Commute (f a) b) : Polynomial A →ₐ[R] B

Polynomial.eval₂ as an AlgHom for noncommutative algebras.

This is Polynomial.eval₂RingHom' for AlgHoms.

Equations

• Polynomial.eval₂AlgHom' f b hf = { toRingHom := Polynomial.eval₂RingHom' (↑f) b hf, commutes' := ⋯ }

def Polynomial.mapAlgHom {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) : Polynomial A →ₐ[R] Polynomial B

Polynomial.map as an AlgHom for noncommutative algebras.

This is the algebra version of Polynomial.mapRingHom.

Equations

• Polynomial.mapAlgHom f = { toRingHom := Polynomial.mapRingHom f.toRingHom, commutes' := ⋯ }

@[simp]

theorem Polynomial.coe_mapAlgHom {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) : ⇑(Polynomial.mapAlgHom f) = Polynomial.map ↑f

@[simp]

theorem Polynomial.mapAlgHom_id {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] : Polynomial.mapAlgHom (AlgHom.id R A) = AlgHom.id R (Polynomial A)

@[simp]

theorem Polynomial.mapAlgHom_coe_ringHom {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) : ↑(Polynomial.mapAlgHom f) = Polynomial.mapRingHom ↑f

@[simp]

theorem Polynomial.mapAlgHom_comp {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (C : Type z) [Semiring C] [Algebra R C] (f : B →ₐ[R] C) (g : A →ₐ[R] B) : (Polynomial.mapAlgHom f).comp (Polynomial.mapAlgHom g) = Polynomial.mapAlgHom (f.comp g)

theorem Polynomial.mapAlgHom_eq_eval₂AlgHom'_CAlgHom {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) : Polynomial.mapAlgHom f = Polynomial.eval₂AlgHom' (Polynomial.CAlgHom.comp f) Polynomial.X ⋯

def Polynomial.mapAlgEquiv {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A ≃ₐ[R] B) : Polynomial A ≃ₐ[R] Polynomial B

If A and B are isomorphic as R-algebras, then so are their polynomial rings

Equations

• Polynomial.mapAlgEquiv f = AlgEquiv.ofAlgHom (Polynomial.mapAlgHom ↑f) (Polynomial.mapAlgHom ↑f.symm) ⋯ ⋯

@[simp]

theorem Polynomial.coe_mapAlgEquiv {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A ≃ₐ[R] B) : ⇑(Polynomial.mapAlgEquiv f) = Polynomial.map ↑f

@[simp]

theorem Polynomial.mapAlgEquiv_id {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] : Polynomial.mapAlgEquiv AlgEquiv.refl = AlgEquiv.refl

@[simp]

theorem Polynomial.mapAlgEquiv_coe_ringHom {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A ≃ₐ[R] B) : ↑(Polynomial.mapAlgEquiv f) = Polynomial.mapRingHom ↑f

@[simp]

theorem Polynomial.mapAlgEquiv_comp {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (C : Type z) [Semiring C] [Algebra R C] (f : A ≃ₐ[R] B) (g : B ≃ₐ[R] C) : (Polynomial.mapAlgEquiv f).trans (Polynomial.mapAlgEquiv g) = Polynomial.mapAlgEquiv (f.trans g)

def Polynomial.aeval {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) : Polynomial R →ₐ[R] A

Given a valuation x of the variable in an R-algebra A, aeval R A x is the unique R-algebra homomorphism from R[X] to A sending X to x.

This is a stronger variant of the linear map Polynomial.leval.

Equations

• Polynomial.aeval x = Polynomial.eval₂AlgHom' (Algebra.ofId R A) x ⋯

@[simp]

theorem Polynomial.adjoin_X {R : Type u} [CommSemiring R] : Algebra.adjoin R {Polynomial.X} = ⊤

theorem Polynomial.algHom_ext {R : Type u} {B : Type u_2} [CommSemiring R] [Semiring B] [Algebra R B] {f : Polynomial R →ₐ[R] B} {g : Polynomial R →ₐ[R] B} (hX : f Polynomial.X = g Polynomial.X) : f = g

theorem Polynomial.aeval_def {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) (p : Polynomial R) : (Polynomial.aeval x) p = Polynomial.eval₂ (algebraMap R A) x p

theorem Polynomial.aeval_zero {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) : (Polynomial.aeval x) 0 = 0

@[simp]

theorem Polynomial.aeval_X {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) : (Polynomial.aeval x) Polynomial.X = x

@[simp]

theorem Polynomial.aeval_C {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) (r : R) : (Polynomial.aeval x) (Polynomial.C r) = (algebraMap R A) r

@[simp]

theorem Polynomial.aeval_monomial {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) {n : ℕ} {r : R} : (Polynomial.aeval x) ((Polynomial.monomial n) r) = (algebraMap R A) r * x ^ n

theorem Polynomial.aeval_X_pow {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) {n : ℕ} : (Polynomial.aeval x) (Polynomial.X ^ n) = x ^ n

theorem Polynomial.aeval_add {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] {p : Polynomial R} {q : Polynomial R} (x : A) : (Polynomial.aeval x) (p + q) = (Polynomial.aeval x) p + (Polynomial.aeval x) q

theorem Polynomial.aeval_one {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) : (Polynomial.aeval x) 1 = 1

theorem Polynomial.aeval_natCast {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) (n : ℕ) : (Polynomial.aeval x) ↑n = ↑n

@[deprecated Polynomial.aeval_natCast]

theorem Polynomial.aeval_nat_cast {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) (n : ℕ) : (Polynomial.aeval x) ↑n = ↑n

Alias of Polynomial.aeval_natCast.

theorem Polynomial.aeval_mul {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] {p : Polynomial R} {q : Polynomial R} (x : A) : (Polynomial.aeval x) (p * q) = (Polynomial.aeval x) p * (Polynomial.aeval x) q

theorem Polynomial.comp_eq_aeval {R : Type u} [CommSemiring R] {p : Polynomial R} {q : Polynomial R} : p.comp q = (Polynomial.aeval q) p

theorem Polynomial.aeval_comp {R : Type u} [CommSemiring R] {p : Polynomial R} {q : Polynomial R} {A : Type u_3} [Semiring A] [Algebra R A] (x : A) : (Polynomial.aeval x) (p.comp q) = (Polynomial.aeval ((Polynomial.aeval x) q)) p

@[simp]

theorem Polynomial.algEquivOfCompEqX_symm_apply {R : Type u} [CommSemiring R] (p : Polynomial R) (q : Polynomial R) (hpq : p.comp q = Polynomial.X) (hqp : q.comp p = Polynomial.X) (a : Polynomial R) : (p.algEquivOfCompEqX q hpq hqp).symm a = (Polynomial.aeval q) a

@[simp]

theorem Polynomial.algEquivOfCompEqX_apply {R : Type u} [CommSemiring R] (p : Polynomial R) (q : Polynomial R) (hpq : p.comp q = Polynomial.X) (hqp : q.comp p = Polynomial.X) (a : Polynomial R) : (p.algEquivOfCompEqX q hpq hqp) a = (Polynomial.aeval p) a

def Polynomial.algEquivOfCompEqX {R : Type u} [CommSemiring R] (p : Polynomial R) (q : Polynomial R) (hpq : p.comp q = Polynomial.X) (hqp : q.comp p = Polynomial.X) : Polynomial R ≃ₐ[R] Polynomial R

Two polynomials p and q such that p(q(X))=X and q(p(X))=X induces an automorphism of the polynomial algebra.

Equations

• p.algEquivOfCompEqX q hpq hqp = AlgEquiv.ofAlgHom (Polynomial.aeval p) (Polynomial.aeval q) ⋯ ⋯

@[simp]

theorem Polynomial.algEquivAevalXAddC_symm_apply {R : Type u_3} [CommRing R] (t : R) (a : Polynomial R) : (Polynomial.algEquivAevalXAddC t).symm a = (Polynomial.aeval (Polynomial.X - Polynomial.C t)) a

@[simp]

theorem Polynomial.algEquivAevalXAddC_apply {R : Type u_3} [CommRing R] (t : R) (a : Polynomial R) : (Polynomial.algEquivAevalXAddC t) a = (Polynomial.aeval (Polynomial.X + Polynomial.C t)) a

def Polynomial.algEquivAevalXAddC {R : Type u_3} [CommRing R] (t : R) : Polynomial R ≃ₐ[R] Polynomial R

The automorphism of the polynomial algebra given by p(X) ↦ p(X+t), with inverse p(X) ↦ p(X-t).

Equations

• Polynomial.algEquivAevalXAddC t = (Polynomial.X + Polynomial.C t).algEquivOfCompEqX (Polynomial.X - Polynomial.C t) ⋯ ⋯

theorem Polynomial.aeval_algHom {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A →ₐ[R] B) (x : A) : Polynomial.aeval (f x) = f.comp (Polynomial.aeval x)

@[simp]

theorem Polynomial.aeval_X_left {R : Type u} [CommSemiring R] : Polynomial.aeval Polynomial.X = AlgHom.id R (Polynomial R)

theorem Polynomial.aeval_X_left_apply {R : Type u} [CommSemiring R] (p : Polynomial R) : (Polynomial.aeval Polynomial.X) p = p

theorem Polynomial.eval_unique {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (φ : Polynomial R →ₐ[R] A) (p : Polynomial R) : φ p = Polynomial.eval₂ (algebraMap R A) (φ Polynomial.X) p

theorem Polynomial.aeval_algHom_apply {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] {F : Type u_3} [FunLike F A B] [AlgHomClass F R A B] (f : F) (x : A) (p : Polynomial R) : (Polynomial.aeval (f x)) p = f ((Polynomial.aeval x) p)

@[simp]

theorem Polynomial.coe_aeval_mk_apply {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] {p : Polynomial R} (x : A) {S : Subalgebra R A} (h : x ∈ S) : ↑((Polynomial.aeval ⟨x, h⟩) p) = (Polynomial.aeval x) p

theorem Polynomial.aeval_algEquiv {R : Type u} {A : Type z} {B : Type u_2} [CommSemiring R] [Semiring A] [Semiring B] [Algebra R A] [Algebra R B] (f : A ≃ₐ[R] B) (x : A) : Polynomial.aeval (f x) = (↑f).comp (Polynomial.aeval x)

theorem Polynomial.aeval_algebraMap_apply_eq_algebraMap_eval {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : R) (p : Polynomial R) : (Polynomial.aeval ((algebraMap R A) x)) p = (algebraMap R A) (Polynomial.eval x p)

@[simp]

theorem Polynomial.coe_aeval_eq_eval {R : Type u} [CommSemiring R] (r : R) : ⇑(Polynomial.aeval r) = Polynomial.eval r

@[simp]

theorem Polynomial.coe_aeval_eq_evalRingHom {R : Type u} [CommSemiring R] (x : R) : ↑(Polynomial.aeval x) = Polynomial.evalRingHom x

@[simp]

theorem Polynomial.aeval_fn_apply {R : Type u} [CommSemiring R] {X : Type u_3} (g : Polynomial R) (f : X → R) (x : X) : (Polynomial.aeval f) g x = (Polynomial.aeval (f x)) g

theorem Polynomial.aeval_subalgebra_coe {R : Type u} [CommSemiring R] (g : Polynomial R) {A : Type u_3} [Semiring A] [Algebra R A] (s : Subalgebra R A) (f : ↥s) : ↑((Polynomial.aeval f) g) = (Polynomial.aeval ↑f) g

theorem Polynomial.coeff_zero_eq_aeval_zero {R : Type u} [CommSemiring R] (p : Polynomial R) : p.coeff 0 = (Polynomial.aeval 0) p

theorem Polynomial.coeff_zero_eq_aeval_zero' {R : Type u} {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (p : Polynomial R) : (algebraMap R A) (p.coeff 0) = (Polynomial.aeval 0) p

theorem Polynomial.map_aeval_eq_aeval_map {R : Type u} [CommSemiring R] {S : Type u_3} {T : Type u_4} {U : Type u_5} [Semiring S] [CommSemiring T] [Semiring U] [Algebra R S] [Algebra T U] {φ : R →+* T} {ψ : S →+* U} (h : (algebraMap T U).comp φ = ψ.comp (algebraMap R S)) (p : Polynomial R) (a : S) : ψ ((Polynomial.aeval a) p) = (Polynomial.aeval (ψ a)) (Polynomial.map φ p)

theorem Polynomial.aeval_eq_zero_of_dvd_aeval_eq_zero {S : Type v} {T : Type w} [CommSemiring S] [CommSemiring T] [Algebra S T] {p : Polynomial S} {q : Polynomial S} (h₁ : p ∣ q) {a : T} (h₂ : (Polynomial.aeval a) p = 0) : (Polynomial.aeval a) q = 0

theorem Algebra.adjoin_singleton_eq_range_aeval (R : Type u) {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) : Algebra.adjoin R {x} = (Polynomial.aeval x).range

@[simp]

theorem Polynomial.aeval_mem_adjoin_singleton (R : Type u) {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] {p : Polynomial R} (x : A) : (Polynomial.aeval x) p ∈ Algebra.adjoin R {x}

instance Polynomial.instCommSemiringAdjoinSingleton (R : Type u) {A : Type z} [CommSemiring R] [Semiring A] [Algebra R A] (x : A) : CommSemiring ↥(Algebra.adjoin R {x})

Equations

• Polynomial.instCommSemiringAdjoinSingleton R x = CommSemiring.mk ⋯

instance Polynomial.instCommRingAdjoinSingleton {R : Type u_3} {A : Type u_4} [CommRing R] [Ring A] [Algebra R A] (x : A) : CommRing ↥(Algebra.adjoin R {x})

Equations

• Polynomial.instCommRingAdjoinSingleton x = CommRing.mk ⋯

theorem Polynomial.aeval_eq_sum_range {R : Type u} {S : Type v} [CommSemiring R] [Semiring S] [Algebra R S] {p : Polynomial R} (x : S) : (Polynomial.aeval x) p = ∑ i ∈ Finset.range (p.natDegree + 1), p.coeff i • x ^ i

theorem Polynomial.aeval_eq_sum_range' {R : Type u} {S : Type v} [CommSemiring R] [Semiring S] [Algebra R S] {p : Polynomial R} {n : ℕ} (hn : p.natDegree < n) (x : S) : (Polynomial.aeval x) p = ∑ i ∈ Finset.range n, p.coeff i • x ^ i

theorem Polynomial.isRoot_of_eval₂_map_eq_zero {R : Type u} {S : Type v} [CommSemiring R] {p : Polynomial R} [Semiring S] {f : R →+* S} (hf : Function.Injective ⇑f) {r : R} : Polynomial.eval₂ f (f r) p = 0 → p.IsRoot r

theorem Polynomial.isRoot_of_aeval_algebraMap_eq_zero {R : Type u} {S : Type v} [CommSemiring R] [Semiring S] [Algebra R S] {p : Polynomial R} (inj : Function.Injective ⇑(algebraMap R S)) {r : R} (hr : (Polynomial.aeval ((algebraMap R S) r)) p = 0) : p.IsRoot r

def Polynomial.aevalTower {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (f : R →ₐ[S] A') (x : A') : Polynomial R →ₐ[S] A'

Version of aeval for defining algebra homs out of R[X] over a smaller base ring than R.

Equations

• Polynomial.aevalTower f x = Polynomial.eval₂AlgHom' f x ⋯

@[simp]

theorem Polynomial.aevalTower_X {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') : (Polynomial.aevalTower g y) Polynomial.X = y

@[simp]

theorem Polynomial.aevalTower_C {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') (x : R) : (Polynomial.aevalTower g y) (Polynomial.C x) = g x

@[simp]

theorem Polynomial.aevalTower_comp_C {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') : (↑(Polynomial.aevalTower g y)).comp Polynomial.C = ↑g

theorem Polynomial.aevalTower_algebraMap {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') (x : R) : (Polynomial.aevalTower g y) ((algebraMap R (Polynomial R)) x) = g x

theorem Polynomial.aevalTower_comp_algebraMap {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') : (↑(Polynomial.aevalTower g y)).comp (algebraMap R (Polynomial R)) = ↑g

theorem Polynomial.aevalTower_toAlgHom {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') (x : R) : (Polynomial.aevalTower g y) ((IsScalarTower.toAlgHom S R (Polynomial R)) x) = g x

@[simp]

theorem Polynomial.aevalTower_comp_toAlgHom {R : Type u} {S : Type v} {A' : Type u_1} [CommSemiring R] [CommSemiring A'] [CommSemiring S] [Algebra S R] [Algebra S A'] (g : R →ₐ[S] A') (y : A') : (Polynomial.aevalTower g y).comp (IsScalarTower.toAlgHom S R (Polynomial R)) = g

@[simp]

theorem Polynomial.aevalTower_id {S : Type v} [CommSemiring S] : Polynomial.aevalTower (AlgHom.id S S) = Polynomial.aeval

@[simp]

theorem Polynomial.aevalTower_ofId {S : Type v} {A' : Type u_1} [CommSemiring A'] [CommSemiring S] [Algebra S A'] : Polynomial.aevalTower (Algebra.ofId S A') = Polynomial.aeval

theorem Polynomial.dvd_term_of_dvd_eval_of_dvd_terms {S : Type v} [CommRing S] {z : S} {p : S} {f : Polynomial S} (i : ℕ) (dvd_eval : p ∣ Polynomial.eval z f) (dvd_terms : ∀ (j : ℕ), j ≠ i → p ∣ f.coeff j * z ^ j) : p ∣ f.coeff i * z ^ i

theorem Polynomial.dvd_term_of_isRoot_of_dvd_terms {S : Type v} [CommRing S] {r : S} {p : S} {f : Polynomial S} (i : ℕ) (hr : f.IsRoot r) (h : ∀ (j : ℕ), j ≠ i → p ∣ f.coeff j * r ^ j) : p ∣ f.coeff i * r ^ i

theorem Polynomial.eval_mul_X_sub_C {R : Type u} [Ring R] {p : Polynomial R} (r : R) : Polynomial.eval r (p * (Polynomial.X - Polynomial.C r)) = 0

The evaluation map is not generally multiplicative when the coefficient ring is noncommutative, but nevertheless any polynomial of the form p * (X - monomial 0 r) is sent to zero when evaluated at r.

This is the key step in our proof of the Cayley-Hamilton theorem.

theorem Polynomial.not_isUnit_X_sub_C {R : Type u} [Ring R] [Nontrivial R] (r : R) : ¬IsUnit (Polynomial.X - Polynomial.C r)

theorem Polynomial.aeval_endomorphism {R : Type u} {M : Type u_3} [CommRing R] [AddCommGroup M] [Module R M] (f : M →ₗ[R] M) (v : M) (p : Polynomial R) : ((Polynomial.aeval f) p) v = p.sum fun (n : ℕ) (b : R) => b • (f ^ n) v

theorem Polynomial.aeval_apply_smul_mem_of_le_comap' {R : Type u} {A : Type z} {M : Type u_3} [CommSemiring R] [AddCommMonoid M] [Module R M] {q : Submodule R M} {m : M} (hm : m ∈ q) (p : Polynomial R) [Semiring A] [Algebra R A] [Module A M] [IsScalarTower R A M] (a : A) (hq : q ≤ Submodule.comap ((Algebra.lsmul R R M) a) q) : (Polynomial.aeval a) p • m ∈ q

theorem Polynomial.aeval_apply_smul_mem_of_le_comap {R : Type u} {M : Type u_3} [CommSemiring R] [AddCommMonoid M] [Module R M] {q : Submodule R M} {m : M} (hm : m ∈ q) (p : Polynomial R) (f : Module.End R M) (hq : q ≤ Submodule.comap f q) : ((Polynomial.aeval f) p) m ∈ q