Algebra norms

We define algebra norms and multiplicative algebra norms.

Main Definitions

• AlgebraNorm : an algebra norm on an R-algebra S is a ring norm on S compatible with the action of R.
• MulAlgebraNorm : a multiplicative algebra norm on an R-algebra S is a multiplicative ring norm on S compatible with the action of R.

Tags

norm, algebra norm

structure AlgebraNorm (R : Type u_1) [SeminormedCommRing R] (S : Type u_2) [Ring S] [Algebra R S] extends RingNorm S, Seminorm R S : Type u_2

An algebra norm on an R-algebra S is a ring norm on S compatible with the action of R.

• toFun : S → ℝ
• map_zero' : self.toFun 0 = 0
• add_le' (r s : S) : self.toFun (r + s) ≤ self.toFun r + self.toFun s
• neg' (r : S) : self.toFun (-r) = self.toFun r
• mul_le' (x y : S) : self.toFun (x * y) ≤ self.toFun x * self.toFun y
• eq_zero_of_map_eq_zero' (x : S) : self.toFun x = 0 → x = 0
• smul' (a : R) (x : S) : self.toFun (a • x) = ‖a‖ * self.toFun x

@[implicit_reducible]

instance instInhabitedAlgebraNorm (K : Type u_1) [NormedField K] : Inhabited (AlgebraNorm K K)

class AlgebraNormClass (F : Type u_1) (R : outParam (Type u_2)) [SeminormedCommRing R] (S : outParam (Type u_3)) [Ring S] [Algebra R S] [FunLike F S ℝ] extends RingNormClass F S ℝ, SeminormClass F R S : Prop

AlgebraNormClass F R S states that F is a type of R-algebra norms on the ring S. You should extend this class when you extend AlgebraNorm.

• map_add_le_add (f : F) (a b : S) : f (a + b) ≤ f a + f b
• map_zero (f : F) : f 0 = 0
• map_neg_eq_map (f : F) (a : S) : f (-a) = f a
• map_mul_le_mul (f : F) (a b : S) : f (a * b) ≤ f a * f b
• eq_zero_of_map_eq_zero (f : F) {a : S} : f a = 0 → a = 0
• map_smul_eq_mul (f : F) (a : R) (x : S) : f (a • x) = ‖a‖ * f x

def AlgebraNorm.toRingSeminorm' {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] (f : AlgebraNorm R S) : RingSeminorm S

The ring seminorm underlying an algebra norm.

@[implicit_reducible]

instance AlgebraNorm.instFunLikeReal {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] : FunLike (AlgebraNorm R S) S ℝ

instance AlgebraNorm.algebraNormClass {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] : AlgebraNormClass (AlgebraNorm R S) R S

theorem AlgebraNorm.toFun_eq_coe {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] (p : AlgebraNorm R S) : p.toFun = ⇑p

theorem AlgebraNorm.ext {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] {p q : AlgebraNorm R S} : (∀ (x : S), p x = q x) → p = q

theorem AlgebraNorm.ext_iff {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] {p q : AlgebraNorm R S} : p = q ↔ ∀ (x : S), p x = q x

theorem AlgebraNorm.extends_norm' {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] {f : AlgebraNorm R S} (hf1 : f 1 = 1) (a : R) : f (a • 1) = ‖a‖

An R-algebra norm such that f 1 = 1 extends the norm on R.

theorem AlgebraNorm.extends_norm {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] {f : AlgebraNorm R S} (hf1 : f 1 = 1) (a : R) : f ((algebraMap R S) a) = ‖a‖

An R-algebra norm such that f 1 = 1 extends the norm on R.

def AlgebraNorm.restriction {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] (A : Subalgebra R S) (f : AlgebraNorm R S) : AlgebraNorm R ↥A

The restriction of an algebra norm to a subalgebra.

def AlgebraNorm.isScalarTower_restriction {R : Type u_1} [SeminormedCommRing R] {S : Type u_2} [Ring S] [Algebra R S] {A : Type u_3} [CommRing A] [Algebra R A] [Algebra A S] [IsScalarTower R A S] (hinj : Function.Injective ⇑(algebraMap A S)) (f : AlgebraNorm R S) : AlgebraNorm R A

The restriction of an algebra norm in a scalar tower.

structure MulAlgebraNorm (R : Type u_1) [SeminormedCommRing R] (S : Type u_2) [Ring S] [Algebra R S] extends MulRingNorm S, Seminorm R S : Type u_2

A multiplicative algebra norm on an R-algebra norm S is a multiplicative ring norm on S compatible with the action of R.

• toFun : S → ℝ
• map_zero' : self.toFun 0 = 0
• add_le' (r s : S) : self.toFun (r + s) ≤ self.toFun r + self.toFun s
• neg' (r : S) : self.toFun (-r) = self.toFun r
• map_one' : self.toFun 1 = 1
• map_mul' (x y : S) : self.toFun (x * y) = self.toFun x * self.toFun y
• eq_zero_of_map_eq_zero' (x : S) : self.toFun x = 0 → x = 0
• smul' (a : R) (x : S) : self.toFun (a • x) = ‖a‖ * self.toFun x

@[implicit_reducible]

instance instInhabitedMulAlgebraNorm (K : Type u_1) [NormedField K] : Inhabited (MulAlgebraNorm K K)

class MulAlgebraNormClass (F : Type u_1) (R : outParam (Type u_2)) [SeminormedCommRing R] (S : outParam (Type u_3)) [Ring S] [Algebra R S] [FunLike F S ℝ] extends MulRingNormClass F S ℝ, SeminormClass F R S : Prop

MulAlgebraNormClass F R S states that F is a type of multiplicative R-algebra norms on the ring S. You should extend this class when you extend MulAlgebraNorm.

• map_add_le_add (f : F) (a b : S) : f (a + b) ≤ f a + f b
• map_zero (f : F) : f 0 = 0
• map_neg_eq_map (f : F) (a : S) : f (-a) = f a
• map_mul (f : F) (x y : S) : f (x * y) = f x * f y
• map_one (f : F) : f 1 = 1
• eq_zero_of_map_eq_zero (f : F) {a : S} : f a = 0 → a = 0
• map_smul_eq_mul (f : F) (a : R) (x : S) : f (a • x) = ‖a‖ * f x

@[implicit_reducible]

instance MulAlgebraNorm.instFunLikeReal {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] : FunLike (MulAlgebraNorm R S) S ℝ

instance MulAlgebraNorm.mulAlgebraNormClass {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] : MulAlgebraNormClass (MulAlgebraNorm R S) R S

theorem MulAlgebraNorm.toFun_eq_coe {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] (p : MulAlgebraNorm R S) : p.toFun = ⇑p

theorem MulAlgebraNorm.ext {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] {p q : MulAlgebraNorm R S} : (∀ (x : S), p x = q x) → p = q

theorem MulAlgebraNorm.ext_iff {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] {p q : MulAlgebraNorm R S} : p = q ↔ ∀ (x : S), p x = q x

theorem MulAlgebraNorm.extends_norm' {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] (f : MulAlgebraNorm R S) (a : R) : f (a • 1) = ‖a‖

A multiplicative R-algebra norm extends the norm on R.

theorem MulAlgebraNorm.extends_norm {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] (f : MulAlgebraNorm R S) (a : R) : f ((algebraMap R S) a) = ‖a‖

A multiplicative R-algebra norm extends the norm on R.

def MulAlgebraNorm.toAlgebraNorm {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] (f : MulAlgebraNorm R S) : AlgebraNorm R S

The algebra norm underlying an multiplicative algebra norm.

@[implicit_reducible]

instance MulAlgebraNorm.instCoeAlgebraNorm {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] : Coe (MulAlgebraNorm R S) (AlgebraNorm R S)

@[simp]

theorem MulAlgebraNorm.coe_AlgebraNorm {R : outParam (Type u_1)} {S : outParam (Type u_2)} [SeminormedCommRing R] [Ring S] [Algebra R S] (f : MulAlgebraNorm R S) : ⇑f.toAlgebraNorm = ⇑f

def NormedAlgebra.toMulAlgebraNorm (K : Type u_1) (L : Type u_2) [NormedField K] [NormedField L] [NormedAlgebra K L] : MulAlgebraNorm K L

Given a normed field extension L / K, the norm on L is a multiplicative K-algebra norm.

@[simp]

theorem NormedAlgebra.toMulAlgebraNorm_apply (K : Type u_1) (L : Type u_2) [NormedField K] [NormedField L] [NormedAlgebra K L] (x : L) : (toMulAlgebraNorm K L) x = ‖x‖

def MulRingNorm.toRingNorm {R : Type u_1} [NonAssocRing R] (f : MulRingNorm R) : RingNorm R

The ring norm underlying a multiplicative ring norm.

theorem MulRingNorm.isPowMul {A : Type u_2} [Ring A] (f : MulRingNorm A) : IsPowMul ⇑f

A multiplicative ring norm is power-multiplicative.