import OAI.Analysis.FactorGeneration.EnergyDescent import OAI.Analysis.FactorGeneration.Expectations import OAI.Analysis.FactorGeneration.MatrixAlgebras import OAI.Analysis.FactorGeneration.UniformPartitions namespace OAI noncomputable section namespace Generator /-! A normal element of a diffuse finite factor has L2 approximations in constructed full dyadic matrix algebras. No prescribed MASA is needed. -/ namespace Tracial open scoped BigOperators section open UltrapowerBridge variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {M : VonNeumannAlgebra H} (τ : TracialRepresentation M) theorem exists_normal_matrix_approximation (hfactor : ∀ c : M.toStarSubalgebra, (∀ a : M.toStarSubalgebra,a*c=c*a) → ∃ z : ℂ,c=z • (1 : M.toStarSubalgebra)) (hdiff : ∀ p : M.toStarSubalgebra,IsStarProjection p → p ≠ 0 → ∃ q : M.toStarSubalgebra,IsStarProjection q ∧ q ≠ 0 ∧ q ≠ p ∧ p*q=q ∧ q*p=q) (x : M.toStarSubalgebra) [IsStarNormal x] (ε : ℝ) (hε : 0 < ε) : ∃ k n : ℕ,n=2^k ∧ ∃ E : MatrixUnitSystem (Fin n) M.toStarSubalgebra, ∃ c : Fin n → ℂ,τ.norm₂ (x-∑ j,c j • E.entry j j) < ε := by obtain ⟨Q,c,hc⟩ := exists_normal_spectral_approximation x (ε/2) (by positivity) obtain ⟨k,R,hn,ht,d,hd⟩ := exists_dyadic_spectral_sum_approximation τ hdiff Q (fun _ : Unit => c) (ε/2) (by positivity) obtain ⟨E,hdiag,hstar,hmul,hsum⟩ := exists_matrixUnits_for_partition τ hfactor R (by rw [hn]; positivity) (fun i j => (ht i).trans (ht j).symm) let F : MatrixUnitSystem (Fin R.size) M.toStarSubalgebra := ⟨E,hstar,hmul,hsum⟩ refine ⟨k,R.size,hn,F,d (),?_⟩ change τ.norm₂ (x-∑ j,d () j • E j j) < ε simp only [hdiag] have he : x-∑ j,d () j • (R.piece j).val = (x-∑ i,c i • (Q.piece i).val)+ ((∑ i,c i • (Q.piece i).val)-∑ j,d () j • (R.piece j).val) := by abel rw [he] exact (τ.norm₂_add_le _ _).trans_lt (by have h₁ := (τ.norm₂_le_norm _).trans_lt hc have h₂ := hd () linarith) end /-! A constructed full matrix algebra reduces the actual relative-commutant expectation energy by a uniform factor for a centered nonzero element. -/ open UltrapowerBridge variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {N D M : VonNeumannAlgebra H} (τ : TracialRepresentation M) theorem commutator_norm₂_bound (a b : M.toStarSubalgebra) : τ.norm₂ (a*b-b*a) ≤ 2*‖a‖*τ.norm₂ b := by have h := norm_sub_le (baseVector τ (a*b)) (baseVector τ (b*a)) change τ.norm₂ (a*b-b*a) ≤ τ.norm₂ (a*b)+τ.norm₂ (b*a) at h have hl := τ.norm₂_mul_le a b have hr := τ.norm₂_mul_le_right b a nlinarith theorem commutator_norm₂_approximation (u v x z : M.toStarSubalgebra) (hc : v*z=z*v) : τ.norm₂ (u*x-x*u) ≤ 2*‖u‖*τ.norm₂ (x-z)+2*‖z‖*τ.norm₂ (u-v) := by have he : u*x-x*u=(u*(x-z)-(x-z)*u)- (z*(u-v)-(u-v)*z) := by simp only [mul_sub,sub_mul] rw [hc] abel rw [he] have h := norm_sub_le (baseVector τ (u*(x-z)-(x-z)*u)) (baseVector τ (z*(u-v)-(u-v)*z)) change τ.norm₂ ((u*(x-z)-(x-z)*u)-(z*(u-v)-(u-v)*z)) ≤ τ.norm₂ (u*(x-z)-(x-z)*u)+τ.norm₂ (z*(u-v)-(u-v)*z) at h exact h.trans (add_le_add (commutator_norm₂_bound τ u (x-z)) (commutator_norm₂_bound τ z (u-v))) theorem expectation_energy_descent_of_unitary_approximation (hDM : D ≤ M) (u : unitary M.toStarSubalgebra) (v x : M.toStarSubalgebra) (hd : τ.norm₂ x ≤ τ.norm₂ (conjugateLinear u x-x)) (hclose : τ.norm₂ ((u : M.toStarSubalgebra)-v) < τ.norm₂ x/(4*(‖x‖+1))) (hc : ∀ z : M.toStarSubalgebra,z.val ∈ D → v*z=z*v) : τ.norm₂ (conditionalExpectation τ hDM x)^2 ≤ (15/16 : ℝ)*τ.norm₂ x^2 := by let z := conditionalExpectation τ hDM x have hcomm := commutator_norm₂_approximation τ (u : M.toStarSubalgebra) v x z (hc z (conditionalExpectation_mem τ hDM x)) have hdisp := displacement_le_commutator τ u x have hu := unitary_norm_le (u : M.toStarSubalgebra) u.property.1 have hz := conditionalExpectation_norm_le τ hDM x have hn : 0 ≤ τ.norm₂ (x-z) := norm_nonneg _ have hδ : 0 ≤ τ.norm₂ ((u : M.toStarSubalgebra)-v) := norm_nonneg _ have hsmall : 4*(‖x‖+1)*τ.norm₂ ((u : M.toStarSubalgebra)-v) < τ.norm₂ x := by have h := (lt_div_iff₀ (by positivity : 0 < 4*(‖x‖+1))).mp hclose nlinarith have hr : τ.norm₂ x/4 ≤ τ.norm₂ (x-z) := by have h₁ := mul_le_mul_of_nonneg_right hu hn have h₂ := mul_le_mul_of_nonneg_right hz hδ nlinarith have hpy := conditionalExpectation_pythagoras τ hDM x change τ.norm₂ z^2+τ.norm₂ (x-z)^2=τ.norm₂ x^2 at hpy nlinarith [sq_nonneg (τ.norm₂ (x-z)-τ.norm₂ x/4), show 0 ≤ τ.norm₂ x from norm_nonneg _] theorem exists_irreducible_matrix_energy_descent (hNM : N ≤ M) (hfactor : ∀ c : N.toStarSubalgebra, (∀ a : N.toStarSubalgebra,a*c=c*a) → ∃ z : ℂ,c=z • (1 : N.toStarSubalgebra)) (hdiff : ∀ p : N.toStarSubalgebra,IsStarProjection p → p ≠ 0 → ∃ q : N.toStarSubalgebra,IsStarProjection q ∧ q ≠ 0 ∧ q ≠ p ∧ p*q=q ∧ q*p=q) (hirr : ∀ c : M.toStarSubalgebra, (∀ a : N.toStarSubalgebra,coordinateInclusion hNM a*c=c*coordinateInclusion hNM a) → ∃ z : ℂ,c=z • (1 : M.toStarSubalgebra)) (x : M.toStarSubalgebra) (hx : x ≠ 0) (ht : τ.trace x=0) : ∃ k n : ℕ,n=2^k ∧ ∃ E : MatrixUnitSystem (Fin n) N.toStarSubalgebra, τ.norm₂ (conditionalExpectation τ (E.map (coordinateInclusion hNM)).relativeVonNeumann_le x)^2 ≤ (15/16 : ℝ)*τ.norm₂ x^2 := by let P := insideAlgebra (M := M) (P := N) obtain ⟨u,hu⟩ := exists_strict_centered_displacement τ P (by intro c hc exact hirr c (fun a => hc ⟨coordinateInclusion hNM a,a.property⟩)) x hx ht let a : N.toStarSubalgebra := ⟨(u.val : M.toStarSubalgebra).val,u.property⟩ let : IsStarNormal a := ⟨by apply Subtype.ext exact congrArg (fun b : M.toStarSubalgebra => b.val) (u.val.property.1.trans u.val.property.2.symm)⟩ have hxpos : 0 < τ.norm₂ x := lt_of_le_of_ne (norm_nonneg _) (fun h => hx ((τ.norm₂_eq_zero_iff x).mp h.symm)) obtain ⟨k,n,hn,E,c,hc⟩ := exists_normal_matrix_approximation (restrictedTrace τ hNM) hfactor hdiff a (τ.norm₂ x/(4*(‖x‖+1))) (by positivity) let F := E.map (coordinateInclusion hNM) let v : M.toStarSubalgebra := ∑ j,c j • F.entry j j refine ⟨k,n,hn,E,expectation_energy_descent_of_unitary_approximation τ F.relativeVonNeumann_le u.val v x hu.le ?_ ?_⟩ · change τ.norm₂ (coordinateInclusion hNM (a-∑ j,c j • E.entry j j)) < _ at hc rw [map_sub,map_sum] at hc simp only [map_smul] at hc exact hc · intro z hz have hz' := ((F.relativeStar_mem z.val).mp hz).2 change (∑ j,c j • F.entry j j)*z=z*(∑ j,c j • F.entry j j) simp only [Finset.sum_mul,Finset.mul_sum,smul_mul_assoc,mul_smul_comm] apply Finset.sum_congr rfl intro j _ exact congrArg (fun b : M.toStarSubalgebra => c j • b) (Subtype.ext (hz' j j)) end Tracial /-! Concrete commutants reverse matrix-algebra inclusion. Expectations are compatible with restriction to an intermediate represented subalgebra. -/ section namespace Tracial open UltrapowerBridge variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {D P M : VonNeumannAlgebra H} (τ : TracialRepresentation M) theorem conditionalExpectation_restricted (hPM : P ≤ M) (hDP : D ≤ P) (x : P.toStarSubalgebra) : conditionalExpectation τ (hDP.trans hPM) (coordinateInclusion hPM x)= coordinateInclusion hPM (conditionalExpectation (restrictedTrace τ hPM) hDP x) := by apply conditionalExpectation_eq_of_orthogonal τ (hDP.trans hPM) · exact conditionalExpectation_mem (restrictedTrace τ hPM) hDP x · intro a let b : insideAlgebra (M := P) (P := D) := ⟨⟨a.val.val,hDP a.property⟩,a.property⟩ exact conditionalExpectation_orthogonal (restrictedTrace τ hPM) hDP x b end Tracial namespace MatrixUnitSystem open UltrapowerBridge Tracial variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {M : VonNeumannAlgebra H} variable {ι κ : Type*} [Fintype ι] [DecidableEq ι] [Fintype κ] [DecidableEq κ] theorem relative_antitone (E : MatrixUnitSystem ι M.toStarSubalgebra) (F : MatrixUnitSystem κ M.toStarSubalgebra) (h : E.algebra ≤ F.algebra) : F.relativeVonNeumann ≤ E.relativeVonNeumann := by intro x hx have hx' := (F.relativeStar_mem x).mp hx apply (E.relativeStar_mem x).mpr refine ⟨hx'.1,?_⟩ let y : M.toStarSubalgebra := ⟨x,hx'.1⟩ have hF : ∀ i j,Commute (F.entry i j) y := fun i j => Subtype.ext (hx'.2 i j) intro i j exact congrArg Subtype.val (((F.commute_algebra_iff y).mpr hF) _ (h (E.entry_mem i j))).eq /-- The product commutant is exactly the commutant of the new system inside of the old commutant, with both algebras represented on the same H. -/ theorem relative_product_inside (E : MatrixUnitSystem ι M.toStarSubalgebra) (F : MatrixUnitSystem κ E.relativeVonNeumann.toStarSubalgebra) (hc : ∀ i j k l,Commute (E.entry i j) ((F.map (coordinateInclusion E.relativeVonNeumann_le)).entry k l)) : (E.product (F.map (coordinateInclusion E.relativeVonNeumann_le)) hc).relativeVonNeumann = F.relativeVonNeumann := by let G := F.map (coordinateInclusion E.relativeVonNeumann_le) apply le_antisymm · intro x hx have hE := E.relative_antitone (E.product G hc) (E.algebra_le_product_left G hc) hx have hG := G.relative_antitone (E.product G hc) (E.algebra_le_product_right G hc) hx exact (F.relativeStar_mem x).mpr ⟨hE,((G.relativeStar_mem x).mp hG).2⟩ · intro x hx have hF := (F.relativeStar_mem x).mp hx have hE := (E.relativeStar_mem x).mp hF.1 apply ((E.product G hc).relativeStar_mem x).mpr refine ⟨hE.1,?_⟩ intro a b change ((E.entry a.1 b.1).val*(F.entry a.2 b.2).val)*x= x*((E.entry a.1 b.1).val*(F.entry a.2 b.2).val) rw [mul_assoc,hF.2,← mul_assoc,hE.2,mul_assoc] end MatrixUnitSystem end /-! Quantitative energy descent retaining a prescribed finite matrix algebra in an irreducible inclusion. All expectations and refinements are constructed. -/ namespace Tracial open UltrapowerBridge variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {N M : VonNeumannAlgebra H} {ι : Type*} [Fintype ι] [DecidableEq ι] theorem exists_compatible_matrix_energy_descent (τ : TracialRepresentation M) (hNM : N ≤ M) (hfactor : ∀ c : N.toStarSubalgebra, (∀ a : N.toStarSubalgebra,a*c=c*a) → ∃ z : ℂ,c=z • (1 : N.toStarSubalgebra)) (hdiff : ∀ p : N.toStarSubalgebra,IsStarProjection p → p ≠ 0 → ∃ q : N.toStarSubalgebra,IsStarProjection q ∧ q ≠ 0 ∧ q ≠ p ∧ p*q=q ∧ q*p=q) (hirr : ∀ c : M.toStarSubalgebra, (∀ a : N.toStarSubalgebra,coordinateInclusion hNM a*c=c*coordinateInclusion hNM a) → ∃ z : ℂ,c=z • (1 : M.toStarSubalgebra)) (E : MatrixUnitSystem ι N.toStarSubalgebra) (o : ι) (x : M.toStarSubalgebra) (ht : τ.trace x=0) (hy : conditionalExpectation τ (E.map (coordinateInclusion hNM)).relativeVonNeumann_le x ≠ 0) : ∃ k n : ℕ,n=2^k ∧ ∃ F : MatrixUnitSystem (Fin n) N.toStarSubalgebra, ∃ hc : ∀ i j l m,Commute (E.entry i j) (F.entry l m), E.algebra ≤ (E.product F hc).algebra ∧ τ.norm₂ (conditionalExpectation τ ((E.product F hc).map (coordinateInclusion hNM)).relativeVonNeumann_le x)^2 ≤ (15/16 : ℝ)*τ.norm₂ (conditionalExpectation τ (E.map (coordinateInclusion hNM)).relativeVonNeumann_le x)^2 := by let EM := E.map (coordinateInclusion hNM) let C := EM.relativeVonNeumann let hCM := EM.relativeVonNeumann_le let y := conditionalExpectation τ hCM x let yC : C.toStarSubalgebra := ⟨y.val,conditionalExpectation_mem τ hCM x⟩ let τC := restrictedTrace τ hCM have hyC : yC ≠ 0 := by intro h apply hy exact Subtype.ext (congrArg (fun b : C.toStarSubalgebra => b.val) h) have htC : τC.trace yC=0 := (conditionalExpectation_trace τ hCM x).trans ht obtain ⟨k,n,hn,G,hG⟩ := exists_irreducible_matrix_energy_descent τC (E.relative_inclusion hNM) (E.relative_scalar_center o hfactor) (E.relative_diffuse o hdiff) (E.relative_irreducible hNM o hirr) yC hyC htC let F := G.map (coordinateInclusion E.relativeVonNeumann_le) have hc : ∀ i j l m,Commute (E.entry i j) (F.entry l m) := by intro i j l m apply Subtype.ext exact ((E.relativeStar_mem (G.entry l m).val).mp (G.entry l m).property).2 i j let GM := G.map (coordinateInclusion (E.relative_inclusion hNM)) have hcM : ∀ i j l m,Commute (EM.entry i j) ((GM.map (coordinateInclusion hCM)).entry l m) := by intro i j l m apply Subtype.ext exact congrArg (fun b : N.toStarSubalgebra => b.val) (hc i j l m).eq have hproduct : ((E.product F hc).map (coordinateInclusion hNM)).relativeVonNeumann = GM.relativeVonNeumann := by convert EM.relative_product_inside GM hcM using 1 rfl let hDC := GM.relativeVonNeumann_le have he : conditionalExpectation τ (hDC.trans hCM) x = coordinateInclusion hCM (conditionalExpectation τC hDC yC) := by rw [← conditionalExpectation_tower τ (hDC.trans hCM) hCM hDC x] exact conditionalExpectation_restricted τ hCM hDC yC refine ⟨k,n,hn,F,hc,E.algebra_le_product_left F hc,?_⟩ have hnorm : τ.norm₂ (conditionalExpectation τ (hDC.trans hCM) x)^2 ≤ (15/16 : ℝ)*τ.norm₂ y^2 := by rw [he] exact hG simpa only [hproduct] using hnorm end Tracial /-! Reindex full matrix units without changing their actual algebra or relative commutant. This keeps iterated constructions indexed by Fin n. -/ namespace MatrixUnitSystem open scoped BigOperators variable {ι κ A : Type*} [Fintype ι] [DecidableEq ι] [Fintype κ] [DecidableEq κ] variable [Ring A] [StarRing A] [Algebra ℂ A] [StarModule ℂ A] def reindex (E : MatrixUnitSystem ι A) (e : κ ≃ ι) : MatrixUnitSystem κ A where entry i j := E.entry (e i) (e j) star_entry i j := E.star_entry _ _ mul_entry i j k l := by simpa only [e.apply_eq_iff_eq] using E.mul_entry (e i) (e j) (e k) (e l) total := (e.sum_comp (fun i => E.entry i i)).trans E.total theorem reindex_algebra (E : MatrixUnitSystem ι A) (e : κ ≃ ι) : (E.reindex e).algebra=E.algebra := by apply le_antisymm · exact ((E.reindex e).algebra_le_iff _).mpr (fun i j => E.entry_mem _ _) · apply (E.algebra_le_iff _).mpr intro i j simpa only [reindex,Equiv.apply_symm_apply] using (E.reindex e).entry_mem (e.symm i) (e.symm j) open UltrapowerBridge variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {N M : VonNeumannAlgebra H} theorem map_algebra_mono (E : MatrixUnitSystem ι N.toStarSubalgebra) (F : MatrixUnitSystem κ N.toStarSubalgebra) (h : E.algebra ≤ F.algebra) (f : N.toStarSubalgebra →⋆ₐ[ℂ] M.toStarSubalgebra) : (E.map f).algebra ≤ (F.map f).algebra := by apply ((E.map f).algebra_le_iff _).mpr intro i j obtain ⟨a,ha⟩ := (F.mem_algebra (E.entry i j)).mp (h (E.entry_mem i j)) change f (E.entry i j) ∈ (F.map f).algebra rw [← ha] simp only [map_sum,map_smul] exact (F.map f).algebra.sum_mem fun k _ => (F.map f).algebra.sum_mem fun l _ => (F.map f).algebra.smul_mem ((F.map f).entry_mem k l) _ theorem mapped_reindex_relative (E : MatrixUnitSystem ι N.toStarSubalgebra) (e : κ ≃ ι) (f : N.toStarSubalgebra →⋆ₐ[ℂ] M.toStarSubalgebra) : ((E.reindex e).map f).relativeVonNeumann=(E.map f).relativeVonNeumann := by apply le_antisymm · exact (E.map f).relative_antitone _ (E.map_algebra_mono _ (E.reindex_algebra e).ge f) · exact ((E.reindex e).map f).relative_antitone _ ((E.reindex e).map_algebra_mono _ (E.reindex_algebra e).le f) end MatrixUnitSystem /-! An actual full matrix algebra of any positive finite size can be constructed in the relative commutant. No commuting matrix units are assumed. -/ namespace Tracial open UltrapowerBridge variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℂ H] [CompleteSpace H] variable {M : VonNeumannAlgebra H} {ι : Type*} [Fintype ι] [DecidableEq ι] theorem exists_commuting_matrix_extension (τ : TracialRepresentation M) (E : MatrixUnitSystem ι M.toStarSubalgebra) (o : ι) (hfactor : ∀ c : M.toStarSubalgebra, (∀ a : M.toStarSubalgebra,a*c=c*a) → ∃ z : ℂ,c=z • (1 : M.toStarSubalgebra)) (hdiff : ∀ p : M.toStarSubalgebra,IsStarProjection p → p ≠ 0 → ∃ q : M.toStarSubalgebra,IsStarProjection q ∧ q ≠ 0 ∧ q ≠ p ∧ p*q=q ∧ q*p=q) (n : ℕ) (hn : 0 < n) : ∃ F : MatrixUnitSystem (Fin n) M.toStarSubalgebra, ∃ hc : ∀ i j k l,Commute (E.entry i j) (F.entry k l), Function.Injective F.hom ∧ (∀ j,τ.trace (F.entry j j)=(((n : ℝ)⁻¹ : ℝ) : ℂ)) ∧ E.algebra ≤ (E.product F hc).algebra ∧ WOTClosed (E.product F hc).concreteAlgebra := by let C := E.relativeVonNeumann let τC := restrictedTrace τ E.relativeVonNeumann_le obtain ⟨Q,hsize,ht⟩ := exists_uniform_trace_partition τC (E.relative_diffuse o hdiff) n (identityProjection C) (n : ℝ)⁻¹ (inv_nonneg.mpr (Nat.cast_nonneg n)) (by change τC.trace 1=(n : ℂ)*(((n : ℝ)⁻¹ : ℝ) : ℂ) simp [τC.trace_one,hn.ne']) subst n obtain ⟨G,hdiag,hG,hGM,hGW⟩ := exists_matrixAlgebra_for_unit_partition τC (E.relative_scalar_center o hfactor) Q hn (fun i j => (ht i).trans (ht j).symm) let f := coordinateInclusion E.relativeVonNeumann_le let F := G.map f have hc : ∀ i j k l,Commute (E.entry i j) (F.entry k l) := by intro i j k l apply Subtype.ext exact ((E.relativeStar_mem (G.entry k l).val).mp (G.entry k l).property).2 i j refine ⟨F,hc,?_,?_,E.algebra_le_product_left F hc, (E.product F hc).concreteAlgebra_wotClosed⟩ · intro a b hab apply hG have hm (a : Matrix (Fin Q.size) (Fin Q.size) ℂ) : F.hom a=f (G.hom a) := by simp only [MatrixUnitSystem.hom_apply,map_sum,map_smul] rfl rw [hm,hm] at hab exact (StarSubalgebra.inclusion_injective E.relativeVonNeumann_le) hab · intro j change τC.trace (G.entry j j)=_ rw [hdiag] exact ht j end Tracial end Generator end end OAI