Currying and uncurrying continuous multilinear maps #
We associate to a continuous multilinear map in n+1 variables (i.e., based on Fin n.succ) two
curried functions, named f.curryLeft (which is a continuous linear map on E 0 taking values
in continuous multilinear maps in n variables) and f.curryRight (which is a continuous
multilinear map in n variables taking values in continuous linear maps on E (last n)).
The inverse operations are called uncurryLeft and uncurryRight.
We also register continuous linear equiv versions of these correspondences, in
continuousMultilinearCurryLeftEquiv and continuousMultilinearCurryRightEquiv.
Main results #
ContinuousMultilinearMap.curryLeft,ContinuousLinearMap.uncurryLeftandcontinuousMultilinearCurryLeftEquivContinuousMultilinearMap.curryRight,ContinuousMultilinearMap.uncurryRightandcontinuousMultilinearCurryRightEquiv.ContinuousMultilinearMap.curryMid,ContinuousLinearMap.uncurryMidandContinuousMultilinearMap.curryMidEquiv
Type variables #
We use the following type variables in this file:
π: aNontriviallyNormedField;ΞΉ,ΞΉ': finite index types with decidable equality;E,Eβ: families of normed vector spaces overπindexed byi : ΞΉ;E': a family of normed vector spaces overπindexed byi' : ΞΉ';Ei: a family of normed vector spaces overπindexed byi : Fin (Nat.succ n);G,G': normed vector spaces overπ.
Left currying #
Given a continuous linear map f from E 0 to continuous multilinear maps on n variables,
construct the corresponding continuous multilinear map on n+1 variables obtained by concatenating
the variables, given by m β¦ f (m 0) (tail m)
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Given a continuous multilinear map f in n+1 variables, split the first variable to obtain
a continuous linear map into continuous multilinear maps in n variables, given by
x β¦ (m β¦ f (cons x m)).
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The space of continuous multilinear maps on Ξ (i : Fin (n+1)), E i is canonically isomorphic to
the space of continuous linear maps from E 0 to the space of continuous multilinear maps on
Ξ (i : Fin n), E i.succ, by separating the first variable. We register this isomorphism in
continuousMultilinearCurryLeftEquiv π E Eβ. The algebraic version (without topology) is given
in multilinearCurryLeftEquiv π E Eβ.
The direct and inverse maps are given by f.curryLeft and f.uncurryLeft. Use these
unless you need the full framework of linear isometric equivs.
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Right currying #
Given a continuous linear map f from continuous multilinear maps on n variables to
continuous linear maps on E 0, construct the corresponding continuous multilinear map on n+1
variables obtained by concatenating the variables, given by m β¦ f (init m) (m (last n)).
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Given a continuous multilinear map f in n+1 variables, split the last variable to obtain
a continuous multilinear map in n variables into continuous linear maps, given by
m β¦ (x β¦ f (snoc m x)).
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The space of continuous multilinear maps on Ξ (i : Fin (n+1)), Ei i is canonically isomorphic to
the space of continuous multilinear maps on Ξ (i : Fin n), Ei <| castSucc i with values in the
space of continuous linear maps on Ei (last n), by separating the last variable. We register this
isomorphism as a continuous linear equiv in continuousMultilinearCurryRightEquiv π Ei G.
The algebraic version (without topology) is given in multilinearCurryRightEquiv π Ei G.
The direct and inverse maps are given by f.curryRight and f.uncurryRight. Use these
unless you need the full framework of linear isometric equivs.
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The space of continuous multilinear maps on Ξ (i : Fin (n+1)), G is canonically isomorphic to
the space of continuous multilinear maps on Ξ (i : Fin n), G with values in the space
of continuous linear maps on G, by separating the last variable. We register this
isomorphism as a continuous linear equiv in continuousMultilinearCurryRightEquiv' π n G G'.
For a version allowing dependent types, see continuousMultilinearCurryRightEquiv. When there
are no dependent types, use the primed version as it helps Lean a lot for unification.
The direct and inverse maps are given by f.curryRight and f.uncurryRight. Use these
unless you need the full framework of linear isometric equivs.
Equations
- continuousMultilinearCurryRightEquiv' π n G G' = continuousMultilinearCurryRightEquiv π (fun (x : Fin n.succ) => G) G'
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Currying a variable in the middle #
Given a continuous linear map from M p to the space of continuous multilinear maps
in n variables M 0, ..., M n with M p removed,
returns a continuous multilinear map in all n + 1 variables.
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Interpret a continuous multilinear map in n + 1 variables
as a continuous linear map in pth variable
with values in the continuous multilinear maps in the other variables.
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ContinuousMultilinearMap.curryMid as a linear isometry equivalence.
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Currying with 0 variables #
The space of multilinear maps with 0 variables is trivial: such a multilinear map is just an
arbitrary constant (note that multilinear maps in 0 variables need not map 0 to 0!).
Therefore, the space of continuous multilinear maps on (Fin 0) β G with values in Eβ is
isomorphic (and even isometric) to Eβ. As this is the zeroth step in the construction of iterated
derivatives, we register this isomorphism.
Associating to a continuous multilinear map in 0 variables the unique value it takes.
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Associating to an element x of a vector space Eβ the continuous multilinear map in 0
variables taking the (unique) value x
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- ContinuousMultilinearMap.uncurry0 π G x = ContinuousMultilinearMap.constOfIsEmpty π (fun (i : Fin 0) => G) x
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The continuous linear isomorphism between elements of a normed space, and continuous multilinear
maps in 0 variables with values in this normed space.
The direct and inverse maps are uncurry0 and curry0. Use these unless you need the full
framework of linear isometric equivs.
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With 1 variable #
Continuous multilinear maps from G^1 to G' are isomorphic with continuous linear maps from
G to G'.
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- continuousMultilinearCurryFin1 π G G' = (continuousMultilinearCurryRightEquiv π (fun (x : Fin 1) => G) G').trans (continuousMultilinearCurryFin0 π G (G βL[π] G'))
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An equivalence of the index set defines a linear isometric equivalence between the spaces of multilinear maps.
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A continuous multilinear map with variables indexed by ΞΉ β ΞΉ' defines a continuous
multilinear map with variables indexed by ΞΉ taking values in the space of continuous multilinear
maps with variables indexed by ΞΉ'.
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A continuous multilinear map with variables indexed by ΞΉ taking values in the space of
continuous multilinear maps with variables indexed by ΞΉ' defines a continuous multilinear map with
variables indexed by ΞΉ β ΞΉ'.
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Linear isometric equivalence between the space of continuous multilinear maps with variables
indexed by ΞΉ β ΞΉ' and the space of continuous multilinear maps with variables indexed by ΞΉ
taking values in the space of continuous multilinear maps with variables indexed by ΞΉ'.
The forward and inverse functions are ContinuousMultilinearMap.currySum
and ContinuousMultilinearMap.uncurrySum. Use this definition only if you need
some properties of LinearIsometryEquiv.
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If s : Finset (Fin n) is a finite set of cardinality k and its complement has cardinality
l, then the space of continuous multilinear maps G [Γn]βL[π] G' of n variables is isomorphic
to the space of continuous multilinear maps G [Γk]βL[π] G [Γl]βL[π] G' of k variables taking
values in the space of continuous multilinear maps of l variables.
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Given a linear map into continuous multilinear maps
B : G βL[π] ContinuousMultilinearMap π E F, one can not always uncurry it as G and E might
live in a different universe. However, one can always lift it to a continuous multilinear map
on (G Γ (Ξ i, E i)) ^ (1 + n), which maps (v_0, ..., v_n) to B (g_0) (u_1, ..., u_n) where
g_0 is the G-coordinate of v_0 and u_i is the E_i coordinate of v_i.
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