refactor: Lint style
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kuotsanhsu
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1053ccaa3a
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6a3bb431bf
4 changed files with 73 additions and 29 deletions
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@ -35,17 +35,24 @@ theorem finAddEquivSigmaCond_false (h : ¬ i < m) : finAddEquivSigmaCond i = ⟨
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end Equiv
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/-- The type family parameterized by `Bool` is finite if each type variant is finite. -/
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instance [M : Fintype m] [N : Fintype n] (b : Bool) : Fintype (cond b m n) := b.rec N M
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/-- The type family parameterized by `Bool` has decidable equality if each type variant is
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decidable. -/
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instance [DecidableEq m] [DecidableEq n] : DecidableEq (Σ b, cond b m n)
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| ⟨true, _⟩, ⟨false, _⟩
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| ⟨false, _⟩, ⟨true, _⟩ => isFalse nofun
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| ⟨false, i⟩, ⟨false, j⟩
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| ⟨true, i⟩, ⟨true, j⟩ => if h : i = j then isTrue (Sigma.eq rfl h) else isFalse fun | rfl => h rfl
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| ⟨true, i⟩, ⟨true, j⟩ =>
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if h : i = j then isTrue (Sigma.eq rfl h) else isFalse fun | rfl => h rfl
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namespace Matrix
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/-- The property of a matrix being upper triangular. See also `Matrix.det_of_upperTriangular`. -/
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abbrev IsUpperTriangular [LT n] [CommRing R] (A : Matrix n n R) := A.BlockTriangular id
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/-- The subtype of upper triangular matrices. -/
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abbrev UpperTriangular (n R) [LT n] [CommRing R] := { A : Matrix n n R // A.IsUpperTriangular }
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end Matrix
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@ -68,15 +75,22 @@ theorem toMatrixOrthonormal_apply_apply (b : OrthonormalBasis n 𝕜 E) (f : Mod
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theorem toMatrixOrthonormal_reindex [Fintype m] [DecidableEq m]
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(b : OrthonormalBasis m 𝕜 E) (e : m ≃ n) (f : Module.End 𝕜 E)
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: toMatrixOrthonormal (b.reindex e) f = Matrix.reindex e e (toMatrixOrthonormal b f) :=
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Matrix.ext fun i j => let c := b.toBasis
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show toMatrix (b.reindex e).toBasis (b.reindex e).toBasis f i j = toMatrix c c f (e.symm i) (e.symm j) by
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rw [b.reindex_toBasis, f.toMatrix_apply, c.repr_reindex_apply, c.reindex_apply, f.toMatrix_apply]
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Matrix.ext fun i j =>
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calc toMatrixOrthonormal (b.reindex e) f i j
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_ = (b.reindex e).repr (f (b.reindex e j)) i := f.toMatrix_apply ..
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_ = b.repr (f (b (e.symm j))) (e.symm i) := by simp
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_ = toMatrixOrthonormal b f (e.symm i) (e.symm j) := Eq.symm <| f.toMatrix_apply ..
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end
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/-- **Don't use this definition directly.** Instead, use `Matrix.schurTriangulationBasis`,
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`Matrix.schurTriangulationUnitary`, and `Matrix.schurTriangulation`. See also
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`LinearMap.SchurTriangulationAux.of` and `Matrix.schurTriangulationAux`. -/
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structure SchurTriangulationAux (f : Module.End 𝕜 E) where
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/-- The dimension of the inner product space `E`. -/
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dim : ℕ
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hdim : Module.finrank 𝕜 E = dim
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/-- An orthonormal basis of `E` that induces an upper triangular form for `f`. -/
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basis : OrthonormalBasis (Fin dim) 𝕜 E
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upperTriangular : (toMatrix basis.toBasis basis.toBasis f).IsUpperTriangular
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@ -84,6 +98,8 @@ end
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variable [IsAlgClosed 𝕜]
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/-- **Don't use this definition directly.** This is the key algorithm behind
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`Matrix.schur_triangulation`. -/
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protected noncomputable def SchurTriangulationAux.of
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[NormedAddCommGroup E] [InnerProductSpace 𝕜 E] [FiniteDimensional 𝕜 E] (f : Module.End 𝕜 E)
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: SchurTriangulationAux f :=
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@ -103,7 +119,8 @@ protected noncomputable def SchurTriangulationAux.of
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suffices ⨆ b, cond b V W = ⊤ from (hV.decomposition this).isInternal _
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(sup_eq_iSup V W).symm.trans Submodule.sup_orthogonal_of_completeSpace
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let B (b : Bool) : OrthonormalBasis (cond b (Fin m) (Fin n)) 𝕜 ↥(cond b V W) := b.rec bW bV
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let bE : OrthonormalBasis (Σ b, cond b (Fin m) (Fin n)) 𝕜 E := int.collectedOrthonormalBasis hV B
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let bE : OrthonormalBasis (Σ b, cond b (Fin m) (Fin n)) 𝕜 E :=
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int.collectedOrthonormalBasis hV B
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let e := Equiv.finAddEquivSigmaCond
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let basis := bE.reindex e.symm
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{
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@ -113,11 +130,13 @@ protected noncomputable def SchurTriangulationAux.of
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upperTriangular := fun i j (hji : j < i) => show toMatrixOrthonormal basis f i j = 0 from
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have hB : ∀ s, bE s = B s.1 s.2
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| ⟨true, i⟩ => show bE ⟨true, i⟩ = bV i from
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show (int.collectedBasis fun b => (B b).toBasis).toOrthonormalBasis _ ⟨true, i⟩ = bV i by simp
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show (int.collectedBasis fun b => (B b).toBasis).toOrthonormalBasis _ ⟨true, i⟩ = bV i
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by simp
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| ⟨false, j⟩ => show bE ⟨false, j⟩ = bW j from
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show (int.collectedBasis fun b => (B b).toBasis).toOrthonormalBasis _ ⟨false, j⟩ = bW j by simp
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show (int.collectedBasis fun b => (B b).toBasis).toOrthonormalBasis _ ⟨false, j⟩ = bW j
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by simp
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have hf {bi i' bj j'} (hi : e i = ⟨bi, i'⟩) (hj : e j = ⟨bj, j'⟩) :=
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calc toMatrixOrthonormal basis f i j
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calc toMatrixOrthonormal basis f i j
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_ = toMatrixOrthonormal bE f (e i) (e j) := by rw [f.toMatrixOrthonormal_reindex] ; rfl
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_ = ⟪bE (e i), f (bE (e j))⟫_𝕜 := f.toMatrixOrthonormal_apply_apply ..
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_ = ⟪(B bi i' : E), f (B bj j')⟫_𝕜 := by rw [hB, hB, hi, hj]
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@ -125,7 +144,7 @@ protected noncomputable def SchurTriangulationAux.of
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if hj : j < m then
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let j' : Fin m := ⟨j, hj⟩
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have hf' {bi i'} (hi : e i = ⟨bi, i'⟩) (h0 : ⟪(B bi i' : E), bV j'⟫_𝕜 = 0) :=
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calc toMatrixOrthonormal basis f i j
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calc toMatrixOrthonormal basis f i j
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_ = ⟪(B bi i' : E), f _⟫_𝕜 := hf hi (Equiv.finAddEquivSigmaCond_true hj)
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_ = ⟪_, f (bV j')⟫_𝕜 := rfl
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_ = 0 :=
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@ -145,7 +164,7 @@ protected noncomputable def SchurTriangulationAux.of
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have hi (h : i < m) : False := hj (Nat.lt_trans hji h)
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let i' : Fin n := i.subNat' hi
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let j' : Fin n := j.subNat' hj
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calc toMatrixOrthonormal basis f i j
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calc toMatrixOrthonormal basis f i j
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_ = ⟪(bW i' : E), f (bW j')⟫_𝕜 :=
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hf (Equiv.finAddEquivSigmaCond_false hi) (Equiv.finAddEquivSigmaCond_false hj)
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_ = ⟪bW i', g (bW j')⟫_𝕜 := by simp [g]
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@ -162,8 +181,10 @@ protected noncomputable def SchurTriangulationAux.of
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}
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termination_by Module.finrank 𝕜 E
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decreasing_by exact
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calc Module.finrank 𝕜 W
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_ < m + Module.finrank 𝕜 W := Nat.lt_add_of_pos_left (Submodule.one_le_finrank_iff.mpr μ.property)
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calc Module.finrank 𝕜 W
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_ < m + Module.finrank 𝕜 W :=
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suffices 0 < m from Nat.lt_add_of_pos_left this
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Submodule.one_le_finrank_iff.mpr μ.property
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_ = Module.finrank 𝕜 E := hdim
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end LinearMap
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@ -173,7 +194,12 @@ namespace Matrix
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a.k.a., `instDecidableEq_mathlib`. -/
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variable [RCLike 𝕜] [IsAlgClosed 𝕜] [Fintype n] [DecidableEq n] [LinearOrder n] (A : Matrix n n 𝕜)
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noncomputable def schurTriangulationAux : OrthonormalBasis n 𝕜 (EuclideanSpace 𝕜 n) × UpperTriangular n 𝕜 :=
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/-- **Don't use this definition directly.** Instead, use `Matrix.schurTriangulationBasis`,
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`Matrix.schurTriangulationUnitary`, and `Matrix.schurTriangulation` for which this is their
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simultaneous definition. This is `LinearMap.SchurTriangulationAux` adapted for matrices in the
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Euclidean space. -/
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noncomputable def schurTriangulationAux
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: OrthonormalBasis n 𝕜 (EuclideanSpace 𝕜 n) × UpperTriangular n 𝕜 :=
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let f := toEuclideanLin A
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let ⟨d, hd, b, hut⟩ := LinearMap.SchurTriangulationAux.of f
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let e : Fin d ≃o n := Fintype.orderIsoFinOfCardEq n (finrank_euclideanSpace.symm.trans hd)
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@ -181,17 +207,24 @@ noncomputable def schurTriangulationAux : OrthonormalBasis n 𝕜 (EuclideanSpac
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let B := LinearMap.toMatrixOrthonormal b' f
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suffices B.IsUpperTriangular from ⟨b', B, this⟩
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fun i j (hji : j < i) =>
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calc LinearMap.toMatrixOrthonormal b' f i j
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_ = LinearMap.toMatrixOrthonormal b f (e.symm i) (e.symm j) := by rw [f.toMatrixOrthonormal_reindex] ; rfl
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calc LinearMap.toMatrixOrthonormal b' f i j
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_ = LinearMap.toMatrixOrthonormal b f (e.symm i) (e.symm j) :=
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by rw [f.toMatrixOrthonormal_reindex] ; rfl
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_ = 0 := hut (e.symm.lt_iff_lt.mpr hji)
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/-- The change of basis that induces the upper triangular form `A.schurTriangulation` of a matrix
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`A` over an algebraically closed field. -/
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noncomputable def schurTriangulationBasis : OrthonormalBasis n 𝕜 (EuclideanSpace 𝕜 n) :=
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A.schurTriangulationAux.1
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/-- The unitary matrix that induces the upper triangular form `A.schurTriangulation` to which a
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matrix `A` over an algebraically closed field is unitarily similar. -/
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noncomputable def schurTriangulationUnitary : unitaryGroup n 𝕜 where
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val := (EuclideanSpace.basisFun n 𝕜).toBasis.toMatrix A.schurTriangulationBasis
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property := OrthonormalBasis.toMatrix_orthonormalBasis_mem_unitary ..
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/-- The upper triangular form induced by `A.schurTriangulationUnitary` to which a matrix `A` over an
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algebraically closed field is unitarily similar. -/
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noncomputable def schurTriangulation : UpperTriangular n 𝕜 :=
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A.schurTriangulationAux.2
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@ -204,11 +237,11 @@ theorem schur_triangulation
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have h : U * A.schurTriangulation.val = A * U :=
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let b := A.schurTriangulationBasis.toBasis
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let c := (EuclideanSpace.basisFun n 𝕜).toBasis
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calc c.toMatrix b * LinearMap.toMatrix b b (toEuclideanLin A)
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calc c.toMatrix b * LinearMap.toMatrix b b (toEuclideanLin A)
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_ = LinearMap.toMatrix c c (toEuclideanLin A) * c.toMatrix b := by simp
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_ = LinearMap.toMatrix c c (toLin c c A) * U := rfl
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_ = A * U := by simp
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calc A
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calc A
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_ = A * U * star U := by simp [mul_assoc]
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_ = U * A.schurTriangulation * star U := by rw [←h]
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