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Mathlib.RingTheory.PowerSeries.Evaluation

Evaluation of power series #

Power series in one indeterminate are the particular case of multivariate power series, for the Unit type of indeterminates. This file provides a simpler syntax.

Let R, S be types, with CommRing R, CommRing S. One assumes that IsTopologicalRing R and UniformAddGroup R, and that S is a complete and separated topological R-algebra, with IsLinearTopology S S, which means there is a basis of neighborhoods of 0 consisting of ideals.

Given φ : R →+* S, a : S, and f : MvPowerSeries σ R, PowerSeries.eval₂ f φ a is the evaluation of the power series f at a. It f is (the coercion of) a polynomial, it coincides with the evaluation of that polynomial. Otherwise, it is defined by density from polynomials; its values are irrelevant unless φ is continuous and a is topologically nilpotent (a ^ n tends to 0 when n tends to infinity).

Under Continuous φ and IsTopologicallyNilpotent a, the following lemmas furnish the properties of evaluation:

We refer to the documentation of MvPowerSeries.eval₂ for more details.

noncomputable def PowerSeries.eval₂ {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] (φ : R →+* S) (a : S) [UniformSpace R] [UniformSpace S] :
PowerSeries RS

Evaluation of a power series f at a point a.

It coincides with the evaluation of f as a polynomial if f is the coercion of a polynomial. Otherwise, it is only relevant if φ is continuous and a is topologically nilpotent.

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    @[simp]
    theorem PowerSeries.eval₂_coe {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] (φ : R →+* S) (a : S) [UniformSpace R] [UniformSpace S] (f : Polynomial R) :
    eval₂ φ a f = Polynomial.eval₂ φ a f
    @[simp]
    theorem PowerSeries.eval₂_C {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] (φ : R →+* S) (a : S) [UniformSpace R] [UniformSpace S] (r : R) :
    eval₂ φ a ((C R) r) = φ r
    @[simp]
    theorem PowerSeries.eval₂_X {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] (φ : R →+* S) (a : S) [UniformSpace R] [UniformSpace S] :
    eval₂ φ a X = a

    The evaluation homomorphism at a on PowerSeries, as a RingHom.

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      theorem PowerSeries.hasSum_eval₂ {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] {φ : R →+* S} {a : S} [UniformSpace R] [UniformSpace S] [UniformAddGroup R] [IsTopologicalSemiring R] [UniformAddGroup S] [T2Space S] [CompleteSpace S] [IsTopologicalRing S] [IsLinearTopology S S] ( : Continuous φ) (ha : IsTopologicallyNilpotent a) (f : PowerSeries R) :
      HasSum (fun (d : ) => φ ((coeff R d) f) * a ^ d) (eval₂ φ a f)
      theorem PowerSeries.eval₂_eq_tsum {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] {φ : R →+* S} {a : S} [UniformSpace R] [UniformSpace S] [UniformAddGroup R] [IsTopologicalSemiring R] [UniformAddGroup S] [T2Space S] [CompleteSpace S] [IsTopologicalRing S] [IsLinearTopology S S] ( : Continuous φ) (ha : IsTopologicallyNilpotent a) (f : PowerSeries R) :
      eval₂ φ a f = ∑' (d : ), φ ((coeff R d) f) * a ^ d
      theorem PowerSeries.eval₂_unique {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] {φ : R →+* S} {a : S} [UniformSpace R] [UniformSpace S] [UniformAddGroup R] [IsTopologicalSemiring R] [UniformAddGroup S] [T2Space S] [CompleteSpace S] [IsTopologicalRing S] [IsLinearTopology S S] ( : Continuous φ) (ha : IsTopologicallyNilpotent a) {ε : PowerSeries RS} ( : Continuous ε) (h : ∀ (p : Polynomial R), ε p = Polynomial.eval₂ φ a p) :
      ε = eval₂ φ a
      theorem PowerSeries.comp_eval₂ {R : Type u_1} [CommRing R] {S : Type u_2} [CommRing S] {φ : R →+* S} {a : S} [UniformSpace R] [UniformSpace S] [UniformAddGroup R] [IsTopologicalSemiring R] [UniformAddGroup S] [T2Space S] [CompleteSpace S] [IsTopologicalRing S] [IsLinearTopology S S] ( : Continuous φ) (ha : IsTopologicallyNilpotent a) {T : Type u_3} [UniformSpace T] [CompleteSpace T] [T2Space T] [CommRing T] [IsTopologicalRing T] [IsLinearTopology T T] [UniformAddGroup T] {ε : S →+* T} ( : Continuous ε) :
      ε eval₂ φ a = eval₂ (ε.comp φ) (ε a)

      For IsTopologicallyNilpotent a, the evaluation homomorphism at a on PowerSeries, as an AlgHom.

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