Theorem: IsStarNormal.spectralRadius_eq_nnnorm
File: Mathlib/Analysis/CstarAlgebra/Spectrum.lean

Proof steps:
state_before: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
⊢ spectralRadius ℂ a = ↑‖a‖₊
state_after: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
tactic: refine (ENNReal.pow_strictMono two_ne_zero).injective ?_
state_before: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
state_after: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
tactic: have heq :
    (fun n : ℕ => (‖(a⋆ * a) ^ n‖₊ : ℝ≥0∞) ^ (1 / n : ℝ)) =
      (fun x => x ^ 2) ∘ fun n : ℕ => (‖a ^ n‖₊ : ℝ≥0∞) ^ (1 / n : ℝ) := by
    funext n
    rw [Function.comp_apply, ← rpow_natCast, ← rpow_mul, mul_comm, rpow_mul, rpow_natCast, ←
      coe_pow, sq, ← nnnorm_star_mul_self, Commute.mul_pow (star_comm_self' a), star_pow]
state_before: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
state_after: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
h₂ : Tendsto ((fun a => a ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)) atTop (𝓝 (spectralRadius ℂ a ^ 2))
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
tactic: have h₂ :=
    ((ENNReal.continuous_pow 2).tendsto (spectralRadius ℂ a)).comp
      (spectrum.pow_nnnorm_pow_one_div_tendsto_nhds_spectralRadius a)
state_before: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
h₂ : Tendsto ((fun a => a ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)) atTop (𝓝 (spectralRadius ℂ a ^ 2))
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
state_after: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
h₂ : Tendsto (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) atTop (𝓝 (spectralRadius ℂ a ^ 2))
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
tactic: rw [← heq] at h₂
state_before: A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
h₂ : Tendsto (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) atTop (𝓝 (spectralRadius ℂ a ^ 2))
⊢ spectralRadius ℂ a ^ 2 = ↑‖a‖₊ ^ 2
state_after: case h.e'_3
A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
h₂ : Tendsto (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) atTop (𝓝 (spectralRadius ℂ a ^ 2))
⊢ ↑‖a‖₊ ^ 2 = spectralRadius ℂ (a⋆ * a)
tactic: convert tendsto_nhds_unique h₂ (pow_nnnorm_pow_one_div_tendsto_nhds_spectralRadius (a⋆ * a))
state_before: case h.e'_3
A : Type u_1
inst✝⁵ : NormedRing A
inst✝⁴ : NormedAlgebra ℂ A
inst✝³ : CompleteSpace A
inst✝² : StarRing A
inst✝¹ : CstarRing A
a : A
inst✝ : IsStarNormal a
heq : (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) = (fun x => x ^ 2) ∘ fun n => ↑‖a ^ n‖₊ ^ (1 / ↑n)
h₂ : Tendsto (fun n => ↑‖(a⋆ * a) ^ n‖₊ ^ (1 / ↑n)) atTop (𝓝 (spectralRadius ℂ a ^ 2))
⊢ ↑‖a‖₊ ^ 2 = spectralRadius ℂ (a⋆ * a)
state_after: no goals
tactic: rw [(IsSelfAdjoint.star_mul_self a).spectralRadius_eq_nnnorm, sq, nnnorm_star_mul_self, coe_mul]