Sesquilinear maps #
This files provides properties about sesquilinear maps and forms. The maps considered are of the
form M₁ →ₛₗ[I₁] M₂ →ₛₗ[I₂] M
, where I₁ : R₁ →+* R
and I₂ : R₂ →+* R
are ring homomorphisms and
M₁
is a module over R₁
, M₂
is a module over R₂
and M
is a module over R
.
Sesquilinear forms are the special case that M₁ = M₂
, M = R₁ = R₂ = R
, and I₁ = RingHom.id R
.
Taking additionally I₂ = RingHom.id R
, then one obtains bilinear forms.
These forms are a special case of the bilinear maps defined in BilinearMap.lean
and all basic
lemmas about construction and elementary calculations are found there.
Main declarations #
IsOrtho
: states that two vectors are orthogonal with respect to a sesquilinear mapIsSymm
,IsAlt
: states that a sesquilinear form is symmetric and alternating, respectivelyorthogonalBilin
: provides the orthogonal complement with respect to sesquilinear form
References #
Tags #
Sesquilinear form, Sesquilinear map,
Orthogonal vectors #
The proposition that two elements of a sesquilinear map space are orthogonal
Instances For
A set of vectors v
is orthogonal with respect to some bilinear map B
if and only
if for all i ≠ j
, B (v i) (v j) = 0
. For orthogonality between two elements, use
BilinForm.isOrtho
Instances For
A set of orthogonal vectors v
with respect to some sesquilinear map B
is linearly
independent if for all i
, B (v i) (v i) ≠ 0
.
Reflexive bilinear maps #
The proposition that a sesquilinear map is reflexive
Instances For
Symmetric bilinear forms #
The proposition that a sesquilinear form is symmetric
Instances For
Alternating bilinear maps #
The proposition that a sesquilinear map is alternating
Instances For
The orthogonal complement #
The orthogonal complement of a submodule N
with respect to some bilinear map is the set of
elements x
which are orthogonal to all elements of N
; i.e., for all y
in N
, B x y = 0
.
Note that for general (neither symmetric nor antisymmetric) bilinear maps this definition has a
chirality; in addition to this "left" orthogonal complement one could define a "right" orthogonal
complement for which, for all y
in N
, B y x = 0
. This variant definition is not currently
provided in mathlib.
Equations
- N.orthogonalBilin B = { carrier := {m : M₁ | ∀ n ∈ N, B.IsOrtho n m}, add_mem' := ⋯, zero_mem' := ⋯, smul_mem' := ⋯ }
Instances For
Given a bilinear form B
and some x
such that B x x ≠ 0
, the span of the singleton of x
is complement to its orthogonal complement.
Adjoint pairs #
Given a pair of modules equipped with bilinear maps, this is the condition for a pair of maps between them to be mutually adjoint.
Instances For
Self-adjoint pairs #
The condition for an endomorphism to be "self-adjoint" with respect to a pair of bilinear maps on the underlying module. In the case that these two maps are identical, this is the usual concept of self adjointness. In the case that one of the maps is the negation of the other, this is the usual concept of skew adjointness.
Equations
- B.IsPairSelfAdjoint F f = B.IsAdjointPair F f f
Instances For
An endomorphism of a module is self-adjoint with respect to a bilinear map if it serves as an adjoint for itself.
Equations
- B.IsSelfAdjoint f = B.IsAdjointPair B f f
Instances For
The set of pair-self-adjoint endomorphisms are a submodule of the type of all endomorphisms.
Equations
- B.isPairSelfAdjointSubmodule F = { carrier := {f : Module.End R M | B.IsPairSelfAdjoint F f}, add_mem' := ⋯, zero_mem' := ⋯, smul_mem' := ⋯ }
Instances For
An endomorphism of a module is skew-adjoint with respect to a bilinear map if its negation serves as an adjoint.
Instances For
The set of self-adjoint endomorphisms of a module with bilinear map is a submodule. (In fact it is a Jordan subalgebra.)
Equations
- B.selfAdjointSubmodule = B.isPairSelfAdjointSubmodule B
Instances For
The set of skew-adjoint endomorphisms of a module with bilinear map is a submodule. (In fact it is a Lie subalgebra.)
Instances For
Nondegenerate bilinear maps #
A bilinear map is called left-separating if
the only element that is left-orthogonal to every other element is 0
; i.e.,
for every nonzero x
in M₁
, there exists y
in M₂
with B x y ≠ 0
.
Instances For
In a non-trivial module, zero is not non-degenerate.
A bilinear map is called right-separating if
the only element that is right-orthogonal to every other element is 0
; i.e.,
for every nonzero y
in M₂
, there exists x
in M₁
with B x y ≠ 0
.
Instances For
A bilinear map is called non-degenerate if it is left-separating and right-separating.
Instances For
A bilinear map is left-separating if and only if it has a trivial kernel.
A bilinear map is right-separating if and only if its flip has a trivial kernel.
The restriction of a reflexive bilinear map B
onto a submodule W
is
nondegenerate if W
has trivial intersection with its orthogonal complement,
that is Disjoint W (W.orthogonalBilin B)
.
An orthogonal basis with respect to a left-separating bilinear map has no self-orthogonal elements.
An orthogonal basis with respect to a right-separating bilinear map has no self-orthogonal elements.
Given an orthogonal basis with respect to a bilinear map, the bilinear map is left-separating if the basis has no elements which are self-orthogonal.
Given an orthogonal basis with respect to a bilinear map, the bilinear map is right-separating if the basis has no elements which are self-orthogonal.
Given an orthogonal basis with respect to a bilinear map, the bilinear map is nondegenerate if the basis has no elements which are self-orthogonal.