Compactly supported smooth bundle sections #
The support of a bundle section is the closure of its nonzero locus, not the support of its
map into the total space: the zero vector varies with the base point. We define this closed
support on native ContMDiffSection, the submodules of sections supported in a prescribed set,
and their compactly supported submodule. The latter is the directed supremum of the
fixed-compact stages. These are algebraic carriers; no topology on section spaces is installed
here.
Smooth scalar multiplication preserves support and compact support. A compactly supported scalar function localizes even a section without compact support, and a cutoff equal to one on the support acts as the identity. These operations provide the support stages and localizations used in test sections and their inductive-limit topologies.
The smoothness of multiplication is supplied by Mathlib's ContMDiff.smul_section.
The closed support of a section: the closure of its nonzero locus in the base.
Instances For
The closed support is the closure of the fibrewise nonzero locus.
The closed support is closed in the base.
A section vanishes off its closed support.
Containment of closed support in a closed set is equivalent to vanishing outside it.
Addition cannot enlarge support beyond the union of the two supports.
Constant scalar multiplication does not enlarge support.
Multiplication by a nonzero scalar preserves closed support.
The submodule of native smooth sections whose closed support lies in K.
Instances For
The fixed-support stages increase with the supporting set.
The submodule of native smooth sections with compact closed support. Its subtype is the algebraic compact-test carrier, before a test-space topology is chosen.
Instances For
A section supported in a compact set has compact support.
Every compactly supported section belongs to a fixed-compact stage.
Fixed-compact support stages form a directed family, using union of compact sets.
The compactly supported submodule is exactly the supremum of its fixed-compact stages. This is an algebraic statement, not an assertion about a final topology.
On a compact base every smooth section has compact support.
Multiplication of sections by a smooth scalar function as a linear map.
Instances For
Scalar-valued C^n functions act on C^n sections by pointwise multiplication.
Evaluation of smooth-function multiplication is fibrewise scalar multiplication.
The scalar-localization linear map agrees with smooth-function multiplication.
Scalar localization is supported in both the scalar support and the section support.
Smooth multiplication preserves each fixed-support stage.
Smooth multiplication preserves compact support of the section.
A compactly supported smooth scalar function localizes any smooth section to compact support, even when the original section is not compactly supported.
A cutoff equal to one on a section's closed support leaves that section unchanged.