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TauCeti.Algebra.AlgebraicGroup.Symplectic.RootSubgroup.Basic

Root subgroups of the symplectic group #

For i : Fin m, the elementary matrices

x_{2eᵢ}(c)  = 1 + c E_{i,m+i},
x_{-2eᵢ}(c) = 1 + c E_{m+i,i}

preserve the standard alternating form. For distinct i,j, products of two commuting elementary matrices similarly give the short roots eᵢ-eⱼ, eᵢ+eⱼ, and -eᵢ-eⱼ. This file promotes all five families to affine group-scheme morphisms 𝔾ₐ → Sp₂ₘ over an arbitrary commutative base ring.

The construction first selects the matrix homomorphism through TauCeti.GLSymplecticFin.RootSubgroupIndex. One shared pipeline constructs its natural map on algebra-valued points, recovers the coordinate Hopf-algebra morphism by full faithfulness of the functor of points, and applies relative spectrum. The long-root composites with the closed immersion Sp₂ₘ → GL₂ₘ are proved to be the corresponding general-linear root subgroups. Thus the factorization through the symplectic equations is recorded scheme-theoretically, over every base.

Main definitions #

References #

@[simp]

Under the symplectic point equivalence, a root point is the selected matrix homomorphism.

Every symplectic root subgroup is injective on algebra-valued points.

Symplectic root point homomorphisms are natural in the value algebra.

The positive long-root homomorphism on A-points, sending c to 1 + c E_{i,m+i} in Sp₂ₘ(A).

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    The negative long-root homomorphism on A-points, sending c to 1 + c E_{m+i,i} in Sp₂ₘ(A).

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      The short-root homomorphism on algebra-valued points.

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        @[simp]

        Under the symplectic point equivalence, the positive long-root point is its elementary transvection.

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        Under the symplectic point equivalence, the negative long-root point is its elementary transvection.

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        Under the symplectic point equivalence, a short-root point is its paired elementary-matrix one-parameter subgroup.

        The positive long-root subgroup is injective on algebra-valued points.

        The negative long-root subgroup is injective on algebra-valued points.

        A short-root subgroup is injective on points over every value algebra.

        The positive long-root subgroup on points is natural in the value algebra.

        The negative long-root subgroup on points is natural in the value algebra.

        theorem TauCeti.Symplectic.mapValue_shortRootSubgroupPoints {R : Type u} [CommRing R] {m : ℕ} {i j : Fin m} {A : Type w} [CommRing A] [Algebra R A] {B : Type v} [CommRing B] [Algebra R B] (family : GLSymplecticFin.ShortRootFamily) (φ : A →ₐ[R] B) (hij : i ≠ j) (q : WithConv (↑(AdditiveGroup.coordinateHopfAlgebra R) →ₐ[R] A)) :

        Short-root point homomorphisms are natural in the value algebra.

        The natural transformation of group-valued points selected by a symplectic root index.

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          The natural transformation of group-valued points attached to a short root.

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            A component of the generic root points map is the constructed point homomorphism.

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            A component of the positive long-root natural transformation is the corresponding point homomorphism.

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            A component of the negative long-root natural transformation is the corresponding point homomorphism.

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            A component of the natural short-root points map is the constructed point homomorphism.

            Precomposition by a root coordinate morphism is its natural map on points.

            Precomposition by the positive long-root coordinate morphism gives its natural point map.

            Precomposition by the negative long-root coordinate morphism gives its natural point map.

            Precomposition by the short-root coordinate morphism is its natural map on points.

            @[simp]

            On a same-universe algebra, a root coordinate morphism induces the constructed point map.

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            On a same-universe algebra, the positive coordinate morphism induces the constructed point homomorphism.

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            On a same-universe algebra, the negative coordinate morphism induces the constructed point homomorphism.

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            On a same-universe algebra, a short-root coordinate morphism induces its point homomorphism.

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            A root coordinate morphism sends the generic symplectic matrix to the identity plus its normalized linear term. Entries are indexed in paired coordinates.

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            The positive long-root coordinate morphism factors the matching general-linear root coordinate morphism through the symplectic quotient.

            @[simp]

            The negative long-root coordinate morphism factors the matching general-linear root coordinate morphism through the symplectic quotient.

            The affine group-scheme morphism selected by a symplectic root index.

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              A symplectic root subgroup on scheme-valued points is its standard root matrix.

              The positive long-root subgroup of Sp₂ₘ attached to 2eᵢ, as an affine group-scheme morphism.

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                The positive long-root subgroup is the relative spectrum of its coordinate morphism, transported to the named source and target schemes.

                The negative long-root subgroup of Sp₂ₘ attached to -2eᵢ, as an affine group-scheme morphism.

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                  The negative long-root subgroup is the relative spectrum of its coordinate morphism, transported to the named source and target schemes.

                  noncomputable def TauCeti.Symplectic.shortRootSubgroup {R : Type u} [CommRing R] {m : ℕ} {i j : Fin m} (family : GLSymplecticFin.ShortRootFamily) (hij : i ≠ j) :

                  The affine group-scheme morphism 𝔾ₐ → Sp₂ₘ attached to a short root.

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                    The short-root subgroup is relative spectrum applied to its coordinate morphism.

                    @[simp]

                    The positive long-root subgroup followed by the symplectic inclusion is the corresponding general-linear root subgroup.

                    @[simp]

                    The negative long-root subgroup followed by the symplectic inclusion is the corresponding general-linear root subgroup.