Affine equivalences #
In this file we define AffineEquiv k P₁ P₂
(notation: P₁ ≃ᵃ[k] P₂
) to be the type of affine
equivalences between P₁
and P₂
, i.e., equivalences such that both forward and inverse maps are
affine maps.
We define the following equivalences:
AffineEquiv.refl k P
: the identity map as anAffineEquiv
;e.symm
: the inverse map of anAffineEquiv
as anAffineEquiv
;e.trans e'
: composition of twoAffineEquiv
s; note that the order followsmathlib
'sCategoryTheory
convention (applye
, thene'
), not the convention used in function composition and compositions of bundled morphisms.
We equip AffineEquiv k P P
with a Group
structure with multiplication corresponding to
composition in AffineEquiv.group
.
Tags #
affine space, affine equivalence
An affine equivalence, denoted P₁ ≃ᵃ[k] P₂
, is an equivalence between affine spaces
such that both forward and inverse maps are affine.
We define it using an Equiv
for the map and a LinearEquiv
for the linear part in order
to allow affine equivalences with good definitional equalities.
- toFun : P₁ → P₂
- invFun : P₂ → P₁
- left_inv : Function.LeftInverse self.invFun self.toFun
- right_inv : Function.RightInverse self.invFun self.toFun
Instances For
An affine equivalence, denoted P₁ ≃ᵃ[k] P₂
, is an equivalence between affine spaces
such that both forward and inverse maps are affine.
We define it using an Equiv
for the map and a LinearEquiv
for the linear part in order
to allow affine equivalences with good definitional equalities.
Equations
Instances For
Reinterpret an AffineEquiv
as an AffineMap
.
Equations
Instances For
Construct an affine equivalence by verifying the relation between the map and its linear part at
one base point. Namely, this function takes a map e : P₁ → P₂
, a linear equivalence
e' : V₁ ≃ₗ[k] V₂
, and a point p
such that for any other point p'
we have
e p' = e' (p' -ᵥ p) +ᵥ e p
.
Equations
Instances For
Inverse of an affine equivalence as an affine equivalence.
Equations
Instances For
See Note [custom simps projection]
Equations
Instances For
See Note [custom simps projection]
Equations
Instances For
Bijective affine maps are affine isomorphisms.
Equations
Instances For
Identity map as an AffineEquiv
.
Equations
Instances For
Composition of two AffineEquiv
alences, applied left to right.
Equations
Instances For
The group of AffineEquiv
s are equivalent to the group of units of AffineMap
.
This is the affine version of LinearMap.GeneralLinearGroup.generalLinearEquiv
.
Equations
Instances For
The map p ↦ v +ᵥ p
as an affine automorphism of an affine space.
Note that there is no need for an AffineMap.constVAdd
as it is always an equivalence.
This is roughly to DistribMulAction.toLinearEquiv
as +ᵥ
is to •
.
Equations
Instances For
A more bundled version of AffineEquiv.constVAdd
.
Equations
Instances For
Fixing a point in affine space, homothety about this point gives a group homomorphism from (the centre of) the units of the scalars into the group of affine equivalences.
Equations
Instances For
x
is the only fixed point of pointReflection x
. This lemma requires
x + x = y + y ↔ x = y
. There is no typeclass to use here, so we add it as an explicit argument.
Interpret a linear equivalence between modules as an affine equivalence.