Smooth fibrewise translation of vector bundles #
Let V be a vector bundle over B and b : X → B a map. A family s x ∈ V (b x) is a section
of V along b, and its total-space map is x ↦ ⟨b x, s x⟩. Fibrewise sums of C^n sections
along the same map are C^n (ContMDiff.add_sectionAlong); for b = id this is Mathlib's
ContMDiff.add_section. So are fibrewise differences (ContMDiff.sub_sectionAlong); for
products with C^n functions, see ContMDiff.smul_totalSpace. Finite sums follow
(ContMDiff.sum_sectionAlong); smoothness of the base map is assumed so that the empty sum, the
zero section along b, is covered. The general form applies to maps defined on the total space
itself, which are sections along the projection. Differences of differentiable sections along a
common base map are differentiable as well
(MDifferentiableWithinAt.sub_sectionAlong).
Consequently a C^n section s of V translates the fibres by a C^n diffeomorphism
p ↦ p + s (π p) of the total space, with inverse the translation by -s
(TauCeti.vectorBundleTranslateDiffeomorph). Like the fibrewise rescaling
TauCeti.vectorBundleScalarDiffeomorph, it preserves the projection and needs no global
trivialization. For the cotangent bundle, translation by a one-form is the basic example of a
fibre-preserving map whose effect on the canonical forms is computed by the one-form.
The fibrewise sum of two C^n sections along the same map is C^n.
The fibrewise sum of two C^n sections along the same map is C^n.
The fibrewise sum of two C^n sections along the same map is C^n.
The fibrewise sum of two C^n sections along the same map is C^n.
A finite sum of C^n sections along a C^n map is C^n within a set at a point.
A finite sum of C^n sections along a C^n map is C^n at a point.
A finite sum of C^n sections along a C^n map is C^n on a set.
A finite sum of C^n sections along a C^n map is C^n.
The fibrewise difference of two C^n sections along the same map is C^n.
The fibrewise difference of two C^n sections along the same map is C^n.
The fibrewise difference of two C^n sections along the same map is C^n.
The fibrewise difference of two C^n sections along the same map is C^n.
The difference of differentiable sections along the same base map is differentiable.
The difference of differentiable sections along the same base map is differentiable.
A C^n section σ of a vector bundle translates the fibres by a C^n diffeomorphism
p ↦ p + σ (π p) of the total space. Its inverse is the translation by -σ.
Instances For
Fibrewise translation by σ adds the value of σ at the base point.
The inverse of the translation by σ is the translation by -σ.
Translation by the zero section is the identity diffeomorphism.
Successive fibre translations add the sections.