Theorem: spectrum.limsup_pow_nnnorm_pow_one_div_le_spectralRadius
File: Mathlib/Analysis/Normed/Algebra/Spectrum.lean

Proof steps:
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
⊢ limsup (fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)) atTop ≤ spectralRadius ℂ a
state_after: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
⊢ ↑r ≤ (limsup (fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)) atTop)⁻¹
tactic: refine ENNReal.inv_le_inv.mp (le_of_forall_pos_nnreal_lt fun r r_pos r_lt => ?_)
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
⊢ ↑r ≤ (limsup (fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)) atTop)⁻¹
state_after: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
⊢ ↑r ≤ liminf (fun i => 1 / ↑‖a ^ i‖₊ ^ (1 / ↑i)) atTop
tactic: simp_rw [inv_limsup, ← one_div]
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
⊢ ↑r ≤ liminf (fun i => 1 / ↑‖a ^ i‖₊ ^ (1 / ↑i)) atTop
state_after: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
p : FormalMultilinearSeries ℂ ℂ A := fun n => ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
⊢ ↑r ≤ liminf (fun i => 1 / ↑‖a ^ i‖₊ ^ (1 / ↑i)) atTop
tactic: let p : FormalMultilinearSeries ℂ ℂ A := fun n =>
    ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
p : FormalMultilinearSeries ℂ ℂ A := fun n => ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
⊢ ↑r ≤ liminf (fun i => 1 / ↑‖a ^ i‖₊ ^ (1 / ↑i)) atTop
state_after: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
p : FormalMultilinearSeries ℂ ℂ A := fun n => ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
⊢ ↑r ≤ p.radius
tactic: suffices h : (r : ℝ≥0∞) ≤ p.radius by
    convert h
    simp only [p, p.radius_eq_liminf, ← norm_toNNReal, norm_mkPiRing]
    congr
    ext n
    rw [norm_toNNReal, ENNReal.coe_rpow_def ‖a ^ n‖₊ (1 / n : ℝ), if_neg]
    exact fun ha => (lt_self_iff_false _).mp
      (ha.2.trans_le (one_div_nonneg.mpr n.cast_nonneg : 0 ≤ (1 / n : ℝ)))
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
p : FormalMultilinearSeries ℂ ℂ A := fun n => ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
⊢ ↑r ≤ p.radius
state_after: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
p : FormalMultilinearSeries ℂ ℂ A := fun n => ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
H₁ :
  HasFPowerSeriesOnBall (fun z => Ring.inverse (1 - z • a)) (cauchyPowerSeries (fun z => Ring.inverse (1 - z • a)) 0 ↑r)
    0 ↑r
⊢ ↑r ≤ p.radius
tactic: have H₁ := (differentiableOn_inverse_one_sub_smul r_lt).hasFPowerSeriesOnBall r_pos
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : NormedRing A
inst✝¹ : NormedAlgebra ℂ A
inst✝ : CompleteSpace A
a : A
r : ℝ≥0
r_pos : 0 < r
r_lt : ↑r < (spectralRadius ℂ a)⁻¹
p : FormalMultilinearSeries ℂ ℂ A := fun n => ContinuousMultilinearMap.mkPiRing ℂ (Fin n) (a ^ n)
H₁ :
  HasFPowerSeriesOnBall (fun z => Ring.inverse (1 - z • a)) (cauchyPowerSeries (fun z => Ring.inverse (1 - z • a)) 0 ↑r)
    0 ↑r
⊢ ↑r ≤ p.radius
state_after: no goals
tactic: exact ((hasFPowerSeriesOnBall_inverse_one_sub_smul ℂ a).exchange_radius H₁).r_le