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Pullback (category theory) In category theory, a branch of mathematics, a pullback (also called a fiber product, fibre product, fibered product or Cartesian square) is the limit of a diagram consisting of two morphisms f : X → Z and g : Y → Z with a common codomain. The pullback is written.
Pullback (differential geometry) Let be a smooth map between smooth manifolds and . Then there is an associated linear map from the space of 1-forms on (the linear space of sections of the cotangent bundle) to the space of 1-forms on . This linear map is known as the pullback (by ), and is frequently denoted by .
The pullback bundle is an example that bridges the notion of a pullback as precomposition, and the notion of a pullback as a Cartesian square. In that example, the base space of a fiber bundle is pulled back, in the sense of precomposition, above. The fibers then travel along with the points in the base space at which they are anchored: the ...
Pullback bundle. In mathematics, a pullback bundle or induced bundle[1][2][3] is the fiber bundle that is induced by a map of its base-space. Given a fiber bundle π : E → B and a continuous map f : B′ → B one can define a "pullback" of E by f as a bundle f*E over B′. The fiber of f*E over a point b′ in B′ is just the fiber of E ...
The limit L of such a diagram is called an equalizer of those morphisms. Kernels. A kernel is a special case of an equalizer where one of the morphisms is a zero morphism. Pullbacks. Let F be a diagram that picks out three objects X, Y, and Z in C, where the only non-identity morphisms are f : X → Z and g : Y → Z.
Vector bundle. The (infinitely extended) Möbius strip is a line bundle over the 1-sphere S1. Locally around every point in S1, it looks like U × R (where U is an open arc including the point), but the total bundle is different from S1 × R (which is a cylinder instead). In mathematics, a vector bundle is a topological construction that makes ...
It leads to the existence of pullback maps in other situations, such as pullback homomorphisms in de Rham cohomology. Formally, let f : M → N be smooth, and let ω be a smooth k-form on N. Then there is a differential form f ∗ ω on M, called the pullback of ω, which captures the behavior of ω as seen relative to f.
The exterior derivative is natural in the technical sense: if f : M → N is a smooth map and Ω k is the contravariant smooth functor that assigns to each manifold the space of k-forms on the manifold, then the following diagram commutes so d( f ∗ ω) = f ∗ dω, where f ∗ denotes the pullback of f .