Continuous multilinear maps
We define continuous multilinear maps as maps from Π(i : ι), M₁ i
to M₂
which are multilinear
and continuous, by extending the space of multilinear maps with a continuity assumption.
Here, M₁ i
and M₂
are modules over a ring R
, and ι
is an arbitrary type, and all these
spaces are also topological spaces.
Main definitions
continuous_multilinear_map R M₁ M₂
is the space of continuous multilinear maps fromΠ(i : ι), M₁ i
toM₂
. We show that it is anR
-module.
Implementation notes
We mostly follow the API of multilinear maps.
Notation
We introduce the notation M [×n]→L[R] M'
for the space of continuous n
-multilinear maps from
M^n
to M'
. This is a particular case of the general notion (where we allow varying dependent
types as the arguments of our continuous multilinear maps), but arguably the most important one,
especially when defining iterated derivatives.
- to_multilinear_map : multilinear_map R M₁ M₂
- cont : continuous c.to_multilinear_map.to_fun
Continuous multilinear maps over the ring R
, from Πi, M₁ i
to M₂
where M₁ i
and M₂
are modules over R
with a topological structure. In applications, there will be compatibility
conditions between the algebraic and the topological structures, but this is not needed for the
definition.
Equations
- continuous_multilinear_map.has_coe_to_fun = {F := λ (f : continuous_multilinear_map R M₁ M₂), (Π (i : ι), M₁ i) → M₂, coe := λ (f : continuous_multilinear_map R M₁ M₂), f.to_multilinear_map.to_fun}
Equations
Equations
- continuous_multilinear_map.has_add = {add := λ (f f' : continuous_multilinear_map R M₁ M₂), {to_multilinear_map := {to_fun := (f.to_multilinear_map + f'.to_multilinear_map).to_fun, map_add' := _, map_smul' := _}, cont := _}}
Equations
- continuous_multilinear_map.add_comm_monoid = {add := has_add.add continuous_multilinear_map.has_add, add_assoc := _, zero := 0, zero_add := _, add_zero := _, add_comm := _}
If f
is a continuous multilinear map, then f.to_continuous_linear_map m i
is the continuous
linear map obtained by fixing all coordinates but i
equal to those of m
, and varying the
i
-th coordinate.
Equations
- f.to_continuous_linear_map m i = {to_linear_map := {to_fun := (f.to_multilinear_map.to_linear_map m i).to_fun, map_add' := _, map_smul' := _}, cont := _}
The cartesian product of two continuous multilinear maps, as a continuous multilinear map.
Equations
- f.prod g = {to_multilinear_map := {to_fun := (f.to_multilinear_map.prod g.to_multilinear_map).to_fun, map_add' := _, map_smul' := _}, cont := _}
If g
is continuous multilinear and f
is continuous linear, then g (f m₁, ..., f mₙ)
is
again a continuous multilinear map, that we call g.comp_continuous_linear_map f
.
Equations
- continuous_multilinear_map.comp_continuous_linear_map R M₃ g f = {to_multilinear_map := {to_fun := (multilinear_map.comp_linear_map R M₃ g.to_multilinear_map f.to_linear_map).to_fun, map_add' := _, map_smul' := _}, cont := _}
In the specific case of continuous multilinear maps on spaces indexed by fin (n+1)
, where one
can build an element of Π(i : fin (n+1)), M i
using cons
, one can express directly the
additivity of a multilinear map along the first variable.
In the specific case of continuous multilinear maps on spaces indexed by fin (n+1)
, where one
can build an element of Π(i : fin (n+1)), M i
using cons
, one can express directly the
multiplicativity of a multilinear map along the first variable.
Additivity of a continuous multilinear map along all coordinates at the same time,
writing f (m + m')
as the sum of f (s.piecewise m m')
over all sets s
.
If f
is continuous multilinear, then f (Σ_{j₁ ∈ A₁} g₁ j₁, ..., Σ_{jₙ ∈ Aₙ} gₙ jₙ)
is the sum
of f (g₁ (r 1), ..., gₙ (r n))
where r
ranges over all functions with r 1 ∈ A₁
, ...,
r n ∈ Aₙ
. This follows from multilinearity by expanding successively with respect to each
coordinate.
If f
is continuous multilinear, then f (Σ_{j₁} g₁ j₁, ..., Σ_{jₙ} gₙ jₙ)
is the sum of
f (g₁ (r 1), ..., gₙ (r n))
where r
ranges over all functions r
. This follows from
multilinearity by expanding successively with respect to each coordinate.
Equations
- continuous_multilinear_map.has_neg = {neg := λ (f : continuous_multilinear_map R M₁ M₂), {to_multilinear_map := {to_fun := (-f.to_multilinear_map).to_fun, map_add' := _, map_smul' := _}, cont := _}}
Equations
- continuous_multilinear_map.add_comm_group = {add := has_add.add continuous_multilinear_map.has_add, add_assoc := _, zero := 0, zero_add := _, add_zero := _, neg := has_neg.neg continuous_multilinear_map.has_neg, add_left_neg := _, add_comm := _}
Multiplicativity of a continuous multilinear map along all coordinates at the same time,
writing f (λ i, c i • m i)
as (∏ i, c i) • f m
.
Equations
- continuous_multilinear_map.has_scalar = {smul := λ (c : R) (f : continuous_multilinear_map R M₁ M₂), {to_multilinear_map := {to_fun := (c • f.to_multilinear_map).to_fun, map_add' := _, map_smul' := _}, cont := _}}
The space of continuous multilinear maps is a module over R
, for the pointwise addition and
scalar multiplication.
Equations
- continuous_multilinear_map.semimodule = semimodule.of_core {to_has_scalar := {smul := has_scalar.smul continuous_multilinear_map.has_scalar}, smul_add := _, add_smul := _, mul_smul := _, one_smul := _}
Linear map version of the map to_multilinear_map
associating to a continuous multilinear map
the corresponding multilinear map.
Equations
- continuous_multilinear_map.to_multilinear_map_linear = {to_fun := λ (f : continuous_multilinear_map R M₁ M₂), f.to_multilinear_map, map_add' := _, map_smul' := _}
Composing a continuous multilinear map with a continuous linear map gives again a continuous multilinear map.
Equations
- g.comp_continuous_multilinear_map f = {to_multilinear_map := {to_fun := (g.to_linear_map.comp_multilinear_map f.to_multilinear_map).to_fun, map_add' := _, map_smul' := _}, cont := _}