- Horizontal bundle
In
mathematics , in the field ofdifferential topology , given:"π":"E"→"M",
a smooth
fiber bundle over asmooth manifold "M", then thevertical bundle V"E" of "E" is the subbundle of thetangent bundle T"E" consisting of the vectors which are tangent to the fibers of "E" over "M". A horizontal bundle is then a particular choice of a subbundle of T"E" which is complementary to V"E", in other words provides acomplementary subspace in each fiber.In full generality, the horizontal bundle concept is one way to formulate the notion of an
Ehresmann connection on afiber bundle . However, the concept is usually applied in more specific contexts.More precisely, if "e" ∈ "E" with
:"π"("e")="x" ∈ "M",
then the vertical space V"e""E" at "e" is the tangent space T"e"("E""x") to the fiber "E""x" through "e". A horizontal bundle then determines an horizontal space H"e""E" such that T"e""E" is the
direct sum of V"e""E" and H"e""E".If "E" is a principal "G"-bundle then the horizontal bundle is usually required to be "G"-invariant: see
Connection (principal bundle) for further details. In particular, this is the case when "E" is theframe bundle , i.e., the set of all frames for the tangent spaces of the manifold, and "G" = GL"n".
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