# Documentation

Mathlib.Analysis.Calculus.FormalMultilinearSeries

# Formal multilinear series #

In this file we define FormalMultilinearSeries 𝕜 E F to be a family of n-multilinear maps for all n, designed to model the sequence of derivatives of a function. In other files we use this notion to define C^n functions (called contDiff in mathlib) and analytic functions.

## Notations #

We use the notation E [×n]→L[𝕜] F for the space of continuous multilinear maps on E^n with values in F. This is the space in which the n-th derivative of a function from E to F lives.

## Tags #

multilinear, formal series

def FormalMultilinearSeries (𝕜 : Type u_1) (E : Type u_2) (F : Type u_3) [Ring 𝕜] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] :
Type (max (max u_3 u_2) 0)

A formal multilinear series over a field 𝕜, from E to F, is given by a family of multilinear maps from E^n to F for all n.

Instances For
instance instAddCommGroupFormalMultilinearSeriesToRing {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] :
instance instInhabitedFormalMultilinearSeriesToRing {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] :
@[simp]
theorem zero_apply {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (n : ) :
= 0
@[simp]
theorem neg_apply {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (f : ) (n : ) :
(-f) n = -f n
theorem FormalMultilinearSeries.ext {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } {q : } (h : ∀ (n : ), p n = q n) :
p = q
theorem FormalMultilinearSeries.ext_iff {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } {q : } :
p = q ∀ (n : ), p n = q n
theorem FormalMultilinearSeries.ne_iff {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } {q : } :
p q n, p n q n
def FormalMultilinearSeries.removeZero {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (p : ) :

Killing the zeroth coefficient in a formal multilinear series

Instances For
@[simp]
theorem FormalMultilinearSeries.removeZero_coeff_zero {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (p : ) :
@[simp]
theorem FormalMultilinearSeries.removeZero_coeff_succ {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (p : ) (n : ) :
= p (n + 1)
theorem FormalMultilinearSeries.removeZero_of_pos {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (p : ) {n : } (h : 0 < n) :
theorem FormalMultilinearSeries.congr {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (p : ) {m : } {n : } {v : Fin mE} {w : Fin nE} (h1 : m = n) (h2 : ∀ (i : ) (him : i < m) (hin : i < n), v { val := i, isLt := him } = w { val := i, isLt := hin }) :
↑(p m) v = ↑(p n) w

Convenience congruence lemma stating in a dependent setting that, if the arguments to a formal multilinear series are equal, then the values are also equal.

def FormalMultilinearSeries.compContinuousLinearMap {𝕜 : Type u} {E : Type v} {F : Type w} {G : Type x} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] [] [Module 𝕜 G] [] [] (p : ) (u : E →L[𝕜] F) :

Composing each term pₙ in a formal multilinear series with (u, ..., u) where u is a fixed continuous linear map, gives a new formal multilinear series p.compContinuousLinearMap u.

Instances For
@[simp]
theorem FormalMultilinearSeries.compContinuousLinearMap_apply {𝕜 : Type u} {E : Type v} {F : Type w} {G : Type x} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] [] [Module 𝕜 G] [] [] (p : ) (u : E →L[𝕜] F) (n : ) (v : Fin nE) :
= ↑(p n) (u v)
def FormalMultilinearSeries.restrictScalars (𝕜 : Type u) {𝕜' : Type u'} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] [CommRing 𝕜'] [SMul 𝕜 𝕜'] [Module 𝕜' E] [] [IsScalarTower 𝕜 𝕜' E] [Module 𝕜' F] [] [IsScalarTower 𝕜 𝕜' F] (p : ) :

Reinterpret a formal 𝕜'-multilinear series as a formal 𝕜-multilinear series.

Instances For
def FormalMultilinearSeries.shift {𝕜 : Type u} {E : Type v} {F : Type w} [] [] (p : ) :

Forgetting the zeroth term in a formal multilinear series, and interpreting the following terms as multilinear maps into E →L[𝕜] F. If p corresponds to the Taylor series of a function, then p.shift is the Taylor series of the derivative of the function.

Instances For
def FormalMultilinearSeries.unshift {𝕜 : Type u} {E : Type v} {F : Type w} [] [] (q : FormalMultilinearSeries 𝕜 E (E →L[𝕜] F)) (z : F) :

Adding a zeroth term to a formal multilinear series taking values in E →L[𝕜] F. This corresponds to starting from a Taylor series for the derivative of a function, and building a Taylor series for the function itself.

Instances For
def ContinuousLinearMap.compFormalMultilinearSeries {𝕜 : Type u} {E : Type v} {F : Type w} {G : Type x} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] [] [Module 𝕜 G] [] [] (f : F →L[𝕜] G) (p : ) :

Composing each term pₙ in a formal multilinear series with a continuous linear map f on the left gives a new formal multilinear series f.compFormalMultilinearSeries p whose general term is f ∘ pₙ.

Instances For
@[simp]
theorem ContinuousLinearMap.compFormalMultilinearSeries_apply {𝕜 : Type u} {E : Type v} {F : Type w} {G : Type x} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] [] [Module 𝕜 G] [] [] (f : F →L[𝕜] G) (p : ) (n : ) :
theorem ContinuousLinearMap.compFormalMultilinearSeries_apply' {𝕜 : Type u} {E : Type v} {F : Type w} {G : Type x} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] [] [Module 𝕜 G] [] [] (f : F →L[𝕜] G) (p : ) (n : ) (v : Fin nE) :
= f (↑(p n) v)
noncomputable def FormalMultilinearSeries.order {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] (p : ) :

The index of the first non-zero coefficient in p (or 0 if all coefficients are zero). This is the order of the isolated zero of an analytic function f at a point if p is the Taylor series of f at that point.

Instances For
@[simp]
theorem FormalMultilinearSeries.order_zero {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] :
theorem FormalMultilinearSeries.ne_zero_of_order_ne_zero {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } (hp : ) :
p 0
theorem FormalMultilinearSeries.order_eq_find {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } [DecidablePred fun n => p n 0] (hp : n, p n 0) :
theorem FormalMultilinearSeries.order_eq_find' {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } [DecidablePred fun n => p n 0] (hp : p 0) :
= Nat.find (_ : n, p n )
theorem FormalMultilinearSeries.order_eq_zero_iff' {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } :
p = 0 p 0 0
theorem FormalMultilinearSeries.order_eq_zero_iff {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } (hp : p 0) :
p 0 0
theorem FormalMultilinearSeries.apply_order_ne_zero {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } (hp : p 0) :
theorem FormalMultilinearSeries.apply_order_ne_zero' {𝕜 : Type u} {E : Type v} {F : Type w} [] [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } (hp : ) :
theorem FormalMultilinearSeries.apply_eq_zero_of_lt_order {𝕜 : Type u} {E : Type v} {F : Type w} [] {n : } [] [Module 𝕜 E] [] [] [] [Module 𝕜 F] [] [] {p : } (hp : ) :
p n = 0
def FormalMultilinearSeries.coeff {𝕜 : Type u} {E : Type v} [] (p : ) (n : ) :
E

The nth coefficient of p when seen as a power series.

Instances For
theorem FormalMultilinearSeries.mkPiField_coeff_eq {𝕜 : Type u} {E : Type v} [] (p : ) (n : ) :
= p n
@[simp]
theorem FormalMultilinearSeries.apply_eq_prod_smul_coeff {𝕜 : Type u} {E : Type v} [] {p : } {n : } {y : Fin n𝕜} :
↑(p n) y = (Finset.prod Finset.univ fun i => y i)
theorem FormalMultilinearSeries.coeff_eq_zero {𝕜 : Type u} {E : Type v} [] {p : } {n : } :
p n = 0
@[simp]
theorem FormalMultilinearSeries.apply_eq_pow_smul_coeff {𝕜 : Type u} {E : Type v} [] {p : } {n : } {z : 𝕜} :
(↑(p n) fun x => z) = z ^ n
@[simp]
theorem FormalMultilinearSeries.norm_apply_eq_norm_coef {𝕜 : Type u} {E : Type v} [] {p : } {n : } :
noncomputable def FormalMultilinearSeries.fslope {𝕜 : Type u} {E : Type v} [] (p : ) :

The formal counterpart of dslope, corresponding to the expansion of (f z - f 0) / z. If f has p as a power series, then dslope f has fslope p as a power series.

Instances For
@[simp]
theorem FormalMultilinearSeries.coeff_fslope {𝕜 : Type u} {E : Type v} [] {p : } {n : } :
@[simp]
theorem FormalMultilinearSeries.coeff_iterate_fslope {𝕜 : Type u} {E : Type v} [] {p : } (k : ) (n : ) :
def constFormalMultilinearSeries (𝕜 : Type u_1) (E : Type u_2) [] [] {F : Type u_3} [] [] (c : F) :

The formal multilinear series where all terms of positive degree are equal to zero, and the term of degree zero is c. It is the power series expansion of the constant function equal to c everywhere.

Instances For
@[simp]
theorem constFormalMultilinearSeries_apply {𝕜 : Type u} {E : Type v} {F : Type w} [] [] {c : F} {n : } (hn : n 0) :
= 0