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Exponential.lean
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Exponential.lean
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/-
Copyright (c) 2021 Anatole Dedecker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anatole Dedecker, Eric Wieser
-/
import Mathlib.Analysis.NormedSpace.Exponential
import Mathlib.Analysis.Calculus.FDeriv.Analytic
import Mathlib.Topology.MetricSpace.CauSeqFilter
/-!
# Calculus results on exponential in a Banach algebra
In this file, we prove basic properties about the derivative of the exponential map `exp 𝕂`
in a Banach algebra `𝔸` over a field `𝕂`. We keep them separate from the main file
`Analysis/NormedSpace/Exponential` in order to minimize dependencies.
## Main results
We prove most results for an arbitrary field `𝕂`, and then specialize to `𝕂 = ℝ` or `𝕂 = ℂ`.
### General case
- `hasStrictFDerivAt_exp_zero_of_radius_pos` : `exp 𝕂` has strict Fréchet derivative
`1 : 𝔸 →L[𝕂] 𝔸` at zero, as long as it converges on a neighborhood of zero
(see also `hasStrictDerivAt_exp_zero_of_radius_pos` for the case `𝔸 = 𝕂`)
- `hasStrictFDerivAt_exp_of_lt_radius` : if `𝕂` has characteristic zero and `𝔸` is commutative,
then given a point `x` in the disk of convergence, `exp 𝕂` has strict Fréchet derivative
`exp 𝕂 x • 1 : 𝔸 →L[𝕂] 𝔸` at x (see also `hasStrictDerivAt_exp_of_lt_radius` for the case
`𝔸 = 𝕂`)
- `hasStrictFDerivAt_exp_smul_const_of_mem_ball`: even when `𝔸` is non-commutative, if we have
an intermediate algebra `𝕊` which is commutative, then the function `(u : 𝕊) ↦ exp 𝕂 (u • x)`,
still has strict Fréchet derivative `exp 𝕂 (t • x) • (1 : 𝕊 →L[𝕂] 𝕊).smulRight x` at `t` if
`t • x` is in the radius of convergence.
### `𝕂 = ℝ` or `𝕂 = ℂ`
- `hasStrictFDerivAt_exp_zero` : `exp 𝕂` has strict Fréchet derivative `1 : 𝔸 →L[𝕂] 𝔸` at zero
(see also `hasStrictDerivAt_exp_zero` for the case `𝔸 = 𝕂`)
- `hasStrictFDerivAt_exp` : if `𝔸` is commutative, then given any point `x`, `exp 𝕂` has strict
Fréchet derivative `exp 𝕂 x • 1 : 𝔸 →L[𝕂] 𝔸` at x (see also `hasStrictDerivAt_exp` for the
case `𝔸 = 𝕂`)
- `hasStrictFDerivAt_exp_smul_const`: even when `𝔸` is non-commutative, if we have
an intermediate algebra `𝕊` which is commutative, then the function `(u : 𝕊) ↦ exp 𝕂 (u • x)`
still has strict Fréchet derivative `exp 𝕂 (t • x) • (1 : 𝔸 →L[𝕂] 𝔸).smulRight x` at `t`.
### Compatibility with `Real.exp` and `Complex.exp`
- `Complex.exp_eq_exp_ℂ` : `Complex.exp = exp ℂ ℂ`
- `Real.exp_eq_exp_ℝ` : `Real.exp = exp ℝ ℝ`
-/
open Filter RCLike ContinuousMultilinearMap NormedField NormedSpace Asymptotics
open scoped Nat Topology ENNReal
section AnyFieldAnyAlgebra
variable {𝕂 𝔸 : Type*} [NontriviallyNormedField 𝕂] [NormedRing 𝔸] [NormedAlgebra 𝕂 𝔸]
[CompleteSpace 𝔸]
/-- The exponential in a Banach algebra `𝔸` over a normed field `𝕂` has strict Fréchet derivative
`1 : 𝔸 →L[𝕂] 𝔸` at zero, as long as it converges on a neighborhood of zero. -/
theorem hasStrictFDerivAt_exp_zero_of_radius_pos (h : 0 < (expSeries 𝕂 𝔸).radius) :
HasStrictFDerivAt (exp 𝕂) (1 : 𝔸 →L[𝕂] 𝔸) 0 := by
convert (hasFPowerSeriesAt_exp_zero_of_radius_pos h).hasStrictFDerivAt
ext x
change x = expSeries 𝕂 𝔸 1 fun _ => x
simp [expSeries_apply_eq, Nat.factorial]
/-- The exponential in a Banach algebra `𝔸` over a normed field `𝕂` has Fréchet derivative
`1 : 𝔸 →L[𝕂] 𝔸` at zero, as long as it converges on a neighborhood of zero. -/
theorem hasFDerivAt_exp_zero_of_radius_pos (h : 0 < (expSeries 𝕂 𝔸).radius) :
HasFDerivAt (exp 𝕂) (1 : 𝔸 →L[𝕂] 𝔸) 0 :=
(hasStrictFDerivAt_exp_zero_of_radius_pos h).hasFDerivAt
end AnyFieldAnyAlgebra
section AnyFieldCommAlgebra
variable {𝕂 𝔸 : Type*} [NontriviallyNormedField 𝕂] [NormedCommRing 𝔸] [NormedAlgebra 𝕂 𝔸]
[CompleteSpace 𝔸]
/-- The exponential map in a commutative Banach algebra `𝔸` over a normed field `𝕂` of
characteristic zero has Fréchet derivative `exp 𝕂 x • 1 : 𝔸 →L[𝕂] 𝔸` at any point `x` in the
disk of convergence. -/
theorem hasFDerivAt_exp_of_mem_ball [CharZero 𝕂] {x : 𝔸}
(hx : x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasFDerivAt (exp 𝕂) (exp 𝕂 x • (1 : 𝔸 →L[𝕂] 𝔸)) x := by
have hpos : 0 < (expSeries 𝕂 𝔸).radius := (zero_le _).trans_lt hx
rw [hasFDerivAt_iff_isLittleO_nhds_zero]
suffices
(fun h => exp 𝕂 x * (exp 𝕂 (0 + h) - exp 𝕂 0 - ContinuousLinearMap.id 𝕂 𝔸 h)) =ᶠ[𝓝 0] fun h =>
exp 𝕂 (x + h) - exp 𝕂 x - exp 𝕂 x • ContinuousLinearMap.id 𝕂 𝔸 h by
refine (IsLittleO.const_mul_left ?_ _).congr' this (EventuallyEq.refl _ _)
rw [← hasFDerivAt_iff_isLittleO_nhds_zero]
exact hasFDerivAt_exp_zero_of_radius_pos hpos
have : ∀ᶠ h in 𝓝 (0 : 𝔸), h ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius :=
EMetric.ball_mem_nhds _ hpos
filter_upwards [this] with _ hh
rw [exp_add_of_mem_ball hx hh, exp_zero, zero_add, ContinuousLinearMap.id_apply, smul_eq_mul]
ring
/-- The exponential map in a commutative Banach algebra `𝔸` over a normed field `𝕂` of
characteristic zero has strict Fréchet derivative `exp 𝕂 x • 1 : 𝔸 →L[𝕂] 𝔸` at any point `x` in
the disk of convergence. -/
theorem hasStrictFDerivAt_exp_of_mem_ball [CharZero 𝕂] {x : 𝔸}
(hx : x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasStrictFDerivAt (exp 𝕂) (exp 𝕂 x • (1 : 𝔸 →L[𝕂] 𝔸)) x :=
let ⟨_, hp⟩ := analyticAt_exp_of_mem_ball x hx
hp.hasFDerivAt.unique (hasFDerivAt_exp_of_mem_ball hx) ▸ hp.hasStrictFDerivAt
end AnyFieldCommAlgebra
section deriv
variable {𝕂 : Type*} [NontriviallyNormedField 𝕂] [CompleteSpace 𝕂]
/-- The exponential map in a complete normed field `𝕂` of characteristic zero has strict derivative
`exp 𝕂 x` at any point `x` in the disk of convergence. -/
theorem hasStrictDerivAt_exp_of_mem_ball [CharZero 𝕂] {x : 𝕂}
(hx : x ∈ EMetric.ball (0 : 𝕂) (expSeries 𝕂 𝕂).radius) :
HasStrictDerivAt (exp 𝕂) (exp 𝕂 x) x := by
simpa using (hasStrictFDerivAt_exp_of_mem_ball hx).hasStrictDerivAt
/-- The exponential map in a complete normed field `𝕂` of characteristic zero has derivative
`exp 𝕂 x` at any point `x` in the disk of convergence. -/
theorem hasDerivAt_exp_of_mem_ball [CharZero 𝕂] {x : 𝕂}
(hx : x ∈ EMetric.ball (0 : 𝕂) (expSeries 𝕂 𝕂).radius) : HasDerivAt (exp 𝕂) (exp 𝕂 x) x :=
(hasStrictDerivAt_exp_of_mem_ball hx).hasDerivAt
/-- The exponential map in a complete normed field `𝕂` of characteristic zero has strict derivative
`1` at zero, as long as it converges on a neighborhood of zero. -/
theorem hasStrictDerivAt_exp_zero_of_radius_pos (h : 0 < (expSeries 𝕂 𝕂).radius) :
HasStrictDerivAt (exp 𝕂) (1 : 𝕂) 0 :=
(hasStrictFDerivAt_exp_zero_of_radius_pos h).hasStrictDerivAt
/-- The exponential map in a complete normed field `𝕂` of characteristic zero has derivative
`1` at zero, as long as it converges on a neighborhood of zero. -/
theorem hasDerivAt_exp_zero_of_radius_pos (h : 0 < (expSeries 𝕂 𝕂).radius) :
HasDerivAt (exp 𝕂) (1 : 𝕂) 0 :=
(hasStrictDerivAt_exp_zero_of_radius_pos h).hasDerivAt
end deriv
section RCLikeAnyAlgebra
variable {𝕂 𝔸 : Type*} [RCLike 𝕂] [NormedRing 𝔸] [NormedAlgebra 𝕂 𝔸] [CompleteSpace 𝔸]
/-- The exponential in a Banach algebra `𝔸` over `𝕂 = ℝ` or `𝕂 = ℂ` has strict Fréchet derivative
`1 : 𝔸 →L[𝕂] 𝔸` at zero. -/
theorem hasStrictFDerivAt_exp_zero : HasStrictFDerivAt (exp 𝕂) (1 : 𝔸 →L[𝕂] 𝔸) 0 :=
hasStrictFDerivAt_exp_zero_of_radius_pos (expSeries_radius_pos 𝕂 𝔸)
/-- The exponential in a Banach algebra `𝔸` over `𝕂 = ℝ` or `𝕂 = ℂ` has Fréchet derivative
`1 : 𝔸 →L[𝕂] 𝔸` at zero. -/
theorem hasFDerivAt_exp_zero : HasFDerivAt (exp 𝕂) (1 : 𝔸 →L[𝕂] 𝔸) 0 :=
hasStrictFDerivAt_exp_zero.hasFDerivAt
end RCLikeAnyAlgebra
section RCLikeCommAlgebra
variable {𝕂 𝔸 : Type*} [RCLike 𝕂] [NormedCommRing 𝔸] [NormedAlgebra 𝕂 𝔸] [CompleteSpace 𝔸]
/-- The exponential map in a commutative Banach algebra `𝔸` over `𝕂 = ℝ` or `𝕂 = ℂ` has strict
Fréchet derivative `exp 𝕂 x • 1 : 𝔸 →L[𝕂] 𝔸` at any point `x`. -/
theorem hasStrictFDerivAt_exp {x : 𝔸} : HasStrictFDerivAt (exp 𝕂) (exp 𝕂 x • (1 : 𝔸 →L[𝕂] 𝔸)) x :=
hasStrictFDerivAt_exp_of_mem_ball ((expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _)
/-- The exponential map in a commutative Banach algebra `𝔸` over `𝕂 = ℝ` or `𝕂 = ℂ` has
Fréchet derivative `exp 𝕂 x • 1 : 𝔸 →L[𝕂] 𝔸` at any point `x`. -/
theorem hasFDerivAt_exp {x : 𝔸} : HasFDerivAt (exp 𝕂) (exp 𝕂 x • (1 : 𝔸 →L[𝕂] 𝔸)) x :=
hasStrictFDerivAt_exp.hasFDerivAt
end RCLikeCommAlgebra
section DerivRCLike
variable {𝕂 : Type*} [RCLike 𝕂]
/-- The exponential map in `𝕂 = ℝ` or `𝕂 = ℂ` has strict derivative `exp 𝕂 x` at any point
`x`. -/
theorem hasStrictDerivAt_exp {x : 𝕂} : HasStrictDerivAt (exp 𝕂) (exp 𝕂 x) x :=
hasStrictDerivAt_exp_of_mem_ball ((expSeries_radius_eq_top 𝕂 𝕂).symm ▸ edist_lt_top _ _)
/-- The exponential map in `𝕂 = ℝ` or `𝕂 = ℂ` has derivative `exp 𝕂 x` at any point `x`. -/
theorem hasDerivAt_exp {x : 𝕂} : HasDerivAt (exp 𝕂) (exp 𝕂 x) x :=
hasStrictDerivAt_exp.hasDerivAt
/-- The exponential map in `𝕂 = ℝ` or `𝕂 = ℂ` has strict derivative `1` at zero. -/
theorem hasStrictDerivAt_exp_zero : HasStrictDerivAt (exp 𝕂) (1 : 𝕂) 0 :=
hasStrictDerivAt_exp_zero_of_radius_pos (expSeries_radius_pos 𝕂 𝕂)
/-- The exponential map in `𝕂 = ℝ` or `𝕂 = ℂ` has derivative `1` at zero. -/
theorem hasDerivAt_exp_zero : HasDerivAt (exp 𝕂) (1 : 𝕂) 0 :=
hasStrictDerivAt_exp_zero.hasDerivAt
end DerivRCLike
theorem Complex.exp_eq_exp_ℂ : Complex.exp = NormedSpace.exp ℂ := by
refine funext fun x => ?_
rw [Complex.exp, exp_eq_tsum_div]
have : CauSeq.IsComplete ℂ norm := Complex.instIsComplete
exact tendsto_nhds_unique x.exp'.tendsto_limit (expSeries_div_summable ℝ x).hasSum.tendsto_sum_nat
theorem Real.exp_eq_exp_ℝ : Real.exp = NormedSpace.exp ℝ := by
ext x; exact mod_cast congr_fun Complex.exp_eq_exp_ℂ x
/-! ### Derivative of $\exp (ux)$ by $u$
Note that since for `x : 𝔸` we have `NormedRing 𝔸` not `NormedCommRing 𝔸`, we cannot deduce
these results from `hasFDerivAt_exp_of_mem_ball` applied to the algebra `𝔸`.
One possible solution for that would be to apply `hasFDerivAt_exp_of_mem_ball` to the
commutative algebra `Algebra.elementalAlgebra 𝕊 x`. Unfortunately we don't have all the required
API, so we leave that to a future refactor (see leanprover-community/mathlib#19062 for discussion).
We could also go the other way around and deduce `hasFDerivAt_exp_of_mem_ball` from
`hasFDerivAt_exp_smul_const_of_mem_ball` applied to `𝕊 := 𝔸`, `x := (1 : 𝔸)`, and `t := x`.
However, doing so would make the aforementioned `elementalAlgebra` refactor harder, so for now we
just prove these two lemmas independently.
A last strategy would be to deduce everything from the more general non-commutative case,
$$\frac{d}{dt}e^{x(t)} = \int_0^1 e^{sx(t)} \left(\frac{d}{dt}e^{x(t)}\right) e^{(1-s)x(t)} ds$$
but this is harder to prove, and typically is shown by going via these results first.
TODO: prove this result too!
-/
section exp_smul
variable {𝕂 𝕊 𝔸 : Type*}
variable (𝕂)
open scoped Topology
open Asymptotics Filter
section MemBall
variable [NontriviallyNormedField 𝕂] [CharZero 𝕂]
variable [NormedCommRing 𝕊] [NormedRing 𝔸]
variable [NormedSpace 𝕂 𝕊] [NormedAlgebra 𝕂 𝔸] [Algebra 𝕊 𝔸] [ContinuousSMul 𝕊 𝔸]
variable [IsScalarTower 𝕂 𝕊 𝔸]
variable [CompleteSpace 𝔸]
theorem hasFDerivAt_exp_smul_const_of_mem_ball (x : 𝔸) (t : 𝕊)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x)) (exp 𝕂 (t • x) • (1 : 𝕊 →L[𝕂] 𝕊).smulRight x) t := by
-- TODO: prove this via `hasFDerivAt_exp_of_mem_ball` using the commutative ring
-- `Algebra.elementalAlgebra 𝕊 x`. See leanprover-community/mathlib#19062 for discussion.
have hpos : 0 < (expSeries 𝕂 𝔸).radius := (zero_le _).trans_lt htx
rw [hasFDerivAt_iff_isLittleO_nhds_zero]
suffices (fun (h : 𝕊) => exp 𝕂 (t • x) *
(exp 𝕂 ((0 + h) • x) - exp 𝕂 ((0 : 𝕊) • x) - ((1 : 𝕊 →L[𝕂] 𝕊).smulRight x) h)) =ᶠ[𝓝 0]
fun h =>
exp 𝕂 ((t + h) • x) - exp 𝕂 (t • x) - (exp 𝕂 (t • x) • (1 : 𝕊 →L[𝕂] 𝕊).smulRight x) h by
apply (IsLittleO.const_mul_left _ _).congr' this (EventuallyEq.refl _ _)
rw [← hasFDerivAt_iff_isLittleO_nhds_zero (f := fun u => exp 𝕂 (u • x))
(f' := (1 : 𝕊 →L[𝕂] 𝕊).smulRight x) (x := 0)]
have : HasFDerivAt (exp 𝕂) (1 : 𝔸 →L[𝕂] 𝔸) ((1 : 𝕊 →L[𝕂] 𝕊).smulRight x 0) := by
rw [ContinuousLinearMap.smulRight_apply, ContinuousLinearMap.one_apply, zero_smul]
exact hasFDerivAt_exp_zero_of_radius_pos hpos
exact this.comp 0 ((1 : 𝕊 →L[𝕂] 𝕊).smulRight x).hasFDerivAt
have : Tendsto (fun h : 𝕊 => h • x) (𝓝 0) (𝓝 0) := by
rw [← zero_smul 𝕊 x]
exact tendsto_id.smul_const x
have : ∀ᶠ h in 𝓝 (0 : 𝕊), h • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius :=
this.eventually (EMetric.ball_mem_nhds _ hpos)
filter_upwards [this] with h hh
have : Commute (t • x) (h • x) := ((Commute.refl x).smul_left t).smul_right h
rw [add_smul t h, exp_add_of_commute_of_mem_ball this htx hh, zero_add, zero_smul, exp_zero,
ContinuousLinearMap.smulRight_apply, ContinuousLinearMap.one_apply,
ContinuousLinearMap.smul_apply, ContinuousLinearMap.smulRight_apply,
ContinuousLinearMap.one_apply, smul_eq_mul, mul_sub_left_distrib, mul_sub_left_distrib, mul_one]
theorem hasFDerivAt_exp_smul_const_of_mem_ball' (x : 𝔸) (t : 𝕊)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x))
(((1 : 𝕊 →L[𝕂] 𝕊).smulRight x).smulRight (exp 𝕂 (t • x))) t := by
convert hasFDerivAt_exp_smul_const_of_mem_ball 𝕂 _ _ htx using 1
ext t'
show Commute (t' • x) (exp 𝕂 (t • x))
exact (((Commute.refl x).smul_left t').smul_right t).exp_right 𝕂
theorem hasStrictFDerivAt_exp_smul_const_of_mem_ball (x : 𝔸) (t : 𝕊)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasStrictFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x))
(exp 𝕂 (t • x) • (1 : 𝕊 →L[𝕂] 𝕊).smulRight x) t :=
let ⟨_, hp⟩ := analyticAt_exp_of_mem_ball (t • x) htx
have deriv₁ : HasStrictFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x)) _ t :=
hp.hasStrictFDerivAt.comp t ((ContinuousLinearMap.id 𝕂 𝕊).smulRight x).hasStrictFDerivAt
have deriv₂ : HasFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x)) _ t :=
hasFDerivAt_exp_smul_const_of_mem_ball 𝕂 x t htx
deriv₁.hasFDerivAt.unique deriv₂ ▸ deriv₁
theorem hasStrictFDerivAt_exp_smul_const_of_mem_ball' (x : 𝔸) (t : 𝕊)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasStrictFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x))
(((1 : 𝕊 →L[𝕂] 𝕊).smulRight x).smulRight (exp 𝕂 (t • x))) t := by
let ⟨_, _⟩ := analyticAt_exp_of_mem_ball (t • x) htx
convert hasStrictFDerivAt_exp_smul_const_of_mem_ball 𝕂 _ _ htx using 1
ext t'
show Commute (t' • x) (exp 𝕂 (t • x))
exact (((Commute.refl x).smul_left t').smul_right t).exp_right 𝕂
variable {𝕂}
theorem hasStrictDerivAt_exp_smul_const_of_mem_ball (x : 𝔸) (t : 𝕂)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasStrictDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (exp 𝕂 (t • x) * x) t := by
simpa using (hasStrictFDerivAt_exp_smul_const_of_mem_ball 𝕂 x t htx).hasStrictDerivAt
theorem hasStrictDerivAt_exp_smul_const_of_mem_ball' (x : 𝔸) (t : 𝕂)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasStrictDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (x * exp 𝕂 (t • x)) t := by
simpa using (hasStrictFDerivAt_exp_smul_const_of_mem_ball' 𝕂 x t htx).hasStrictDerivAt
theorem hasDerivAt_exp_smul_const_of_mem_ball (x : 𝔸) (t : 𝕂)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (exp 𝕂 (t • x) * x) t :=
(hasStrictDerivAt_exp_smul_const_of_mem_ball x t htx).hasDerivAt
theorem hasDerivAt_exp_smul_const_of_mem_ball' (x : 𝔸) (t : 𝕂)
(htx : t • x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
HasDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (x * exp 𝕂 (t • x)) t :=
(hasStrictDerivAt_exp_smul_const_of_mem_ball' x t htx).hasDerivAt
end MemBall
section RCLike
variable [RCLike 𝕂]
variable [NormedCommRing 𝕊] [NormedRing 𝔸]
variable [NormedAlgebra 𝕂 𝕊] [NormedAlgebra 𝕂 𝔸] [Algebra 𝕊 𝔸] [ContinuousSMul 𝕊 𝔸]
variable [IsScalarTower 𝕂 𝕊 𝔸]
variable [CompleteSpace 𝔸]
theorem hasFDerivAt_exp_smul_const (x : 𝔸) (t : 𝕊) :
HasFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x)) (exp 𝕂 (t • x) • (1 : 𝕊 →L[𝕂] 𝕊).smulRight x) t :=
hasFDerivAt_exp_smul_const_of_mem_ball 𝕂 _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
theorem hasFDerivAt_exp_smul_const' (x : 𝔸) (t : 𝕊) :
HasFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x))
(((1 : 𝕊 →L[𝕂] 𝕊).smulRight x).smulRight (exp 𝕂 (t • x))) t :=
hasFDerivAt_exp_smul_const_of_mem_ball' 𝕂 _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
theorem hasStrictFDerivAt_exp_smul_const (x : 𝔸) (t : 𝕊) :
HasStrictFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x))
(exp 𝕂 (t • x) • (1 : 𝕊 →L[𝕂] 𝕊).smulRight x) t :=
hasStrictFDerivAt_exp_smul_const_of_mem_ball 𝕂 _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
theorem hasStrictFDerivAt_exp_smul_const' (x : 𝔸) (t : 𝕊) :
HasStrictFDerivAt (fun u : 𝕊 => exp 𝕂 (u • x))
(((1 : 𝕊 →L[𝕂] 𝕊).smulRight x).smulRight (exp 𝕂 (t • x))) t :=
hasStrictFDerivAt_exp_smul_const_of_mem_ball' 𝕂 _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
variable {𝕂}
theorem hasStrictDerivAt_exp_smul_const (x : 𝔸) (t : 𝕂) :
HasStrictDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (exp 𝕂 (t • x) * x) t :=
hasStrictDerivAt_exp_smul_const_of_mem_ball _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
theorem hasStrictDerivAt_exp_smul_const' (x : 𝔸) (t : 𝕂) :
HasStrictDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (x * exp 𝕂 (t • x)) t :=
hasStrictDerivAt_exp_smul_const_of_mem_ball' _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
theorem hasDerivAt_exp_smul_const (x : 𝔸) (t : 𝕂) :
HasDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (exp 𝕂 (t • x) * x) t :=
hasDerivAt_exp_smul_const_of_mem_ball _ _ <| (expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
theorem hasDerivAt_exp_smul_const' (x : 𝔸) (t : 𝕂) :
HasDerivAt (fun u : 𝕂 => exp 𝕂 (u • x)) (x * exp 𝕂 (t • x)) t :=
hasDerivAt_exp_smul_const_of_mem_ball' _ _ <|
(expSeries_radius_eq_top 𝕂 𝔸).symm ▸ edist_lt_top _ _
end RCLike
end exp_smul
section tsum_tprod
variable {𝕂 𝔸 : Type*} [RCLike 𝕂] [NormedCommRing 𝔸] [NormedAlgebra 𝕂 𝔸] [CompleteSpace 𝔸]
/-- If `f` has sum `a`, then `exp ∘ f` has product `exp a`. -/
lemma HasSum.exp {ι : Type*} {f : ι → 𝔸} {a : 𝔸} (h : HasSum f a) :
HasProd (exp 𝕂 ∘ f) (exp 𝕂 a) :=
Tendsto.congr (fun s ↦ exp_sum s f) <| Tendsto.exp h
end tsum_tprod