Basic properties of the manifold Fréchet derivative #
In this file, we show various properties of the manifold Fréchet derivative, mimicking the API for Fréchet derivatives.
- basic properties of unique differentiability sets
- various general lemmas about the manifold Fréchet derivative
- deducing differentiability from smoothness,
- deriving continuity from differentiability on manifolds,
- congruence lemmas for derivatives on manifolds
- composition lemmas and the chain rule
Unique differentiability sets in manifolds #
Relating differentiability in a manifold and differentiability in the model space #
through extended charts
One can reformulate smoothness within a set at a point as continuity within this set at this point, and smoothness in the corresponding extended chart.
One can reformulate smoothness within a set at a point as continuity within this set at this
point, and smoothness in the corresponding extended chart. This form states smoothness of f
written in such a way that the set is restricted to lie within the domain/codomain of the
corresponding charts.
Even though this expression is more complicated than the one in mdifferentiableWithinAt_iff
, it is
a smaller set, but their germs at extChartAt I x x
are equal. It is sometimes useful to rewrite
using this in the goal.
One can reformulate smoothness within a set at a point as continuity within this set at this point, and smoothness in the corresponding extended chart in the target.
An alternative formulation of mdifferentiableWithinAt_iff_of_mem_maximalAtlas
if the set if s
lies in e.source
.
One can reformulate smoothness within a set at a point as continuity within this set at this point, and smoothness in any chart containing that point.
One can reformulate smoothness within a set at a point as continuity within this set at this
point, and smoothness in any chart containing that point. Version requiring differentiability
in the target instead of range I
.
Differentiability on a set is equivalent to differentiability in the extended charts.
If the set where you want f
to be smooth lies entirely in a single chart, and f
maps it
into a single chart, the smoothness of f
on that set can be expressed by purely looking in
these charts.
Note: this lemma uses extChartAt I x '' s
instead of (extChartAt I x).symm ⁻¹' s
to ensure
that this set lies in (extChartAt I x).target
.
If the set where you want f
to be smooth lies entirely in a single chart, and f
maps it
into a single chart, the smoothness of f
on that set can be expressed by purely looking in
these charts.
Note: this lemma uses extChartAt I x '' s
instead of (extChartAt I x).symm ⁻¹' s
to ensure
that this set lies in (extChartAt I x).target
.
One can reformulate smoothness on a set as continuity on this set, and smoothness in any extended chart.
One can reformulate smoothness on a set as continuity on this set, and smoothness in any extended chart in the target.
One can reformulate smoothness as continuity and smoothness in any extended chart.
One can reformulate smoothness as continuity and smoothness in any extended chart in the target.
Deducing differentiability from smoothness #
Deriving continuity from differentiability on manifolds #
UniqueMDiffWithinAt
achieves its goal: it implies the uniqueness of the derivative.
General lemmas on derivatives of functions between manifolds #
We mimic the API for functions between vector spaces
Alias of the reverse direction of hasMFDerivWithinAt_insert
.
Alias of the forward direction of hasMFDerivWithinAt_insert
.
Alias of the reverse direction of mdifferentiableWithinAt_insert
.
Alias of the forward direction of mdifferentiableWithinAt_insert
.
Deriving continuity from differentiability on manifolds #
If two sets coincide locally around x
, except maybe at a point y
, then their
preimage under extChartAt x
coincide locally, except maybe at extChartAt I x x
.
Congruence lemmas for derivatives on manifolds #
If two sets coincide locally, except maybe at a point, then it is equivalent to have a manifold derivative within one or the other.
If two sets coincide around a point (except possibly at a single point y
), then it is
equivalent to be differentiable within one or the other set.
If two sets coincide locally, except maybe at a point, then derivatives within these sets are the same.
If two sets coincide locally, then derivatives within these sets are the same.
If two sets coincide locally, except maybe at a point, then derivatives within these sets coincide locally.
If two sets coincide locally, then derivatives within these sets coincide locally.
A congruence lemma for mfderiv
, (ab)using the fact that TangentSpace I' (f x)
is
definitionally equal to E'
.
A congruence lemma for mfderiv
, (ab)using the fact that TangentSpace I' (f x)
is
definitionally equal to E'
.
Composition lemmas #
The chain rule for manifolds.