In
differential geometry, the exponential map is a generalization of the ordinary
exponential function
The exponential function is a mathematical function denoted by f(x)=\exp(x) or e^x (where the argument is written as an exponent). Unless otherwise specified, the term generally refers to the positive-valued function of a real variable, ...
of mathematical analysis. Important special cases include:
*
exponential map (Riemannian geometry)
In Riemannian geometry, an exponential map is a map from a subset of a tangent space T''p'M'' of a Riemannian manifold (or pseudo-Riemannian manifold) ''M'' to ''M'' itself. The (pseudo) Riemannian metric determines a canonical affine connect ...
for a manifold with a Riemannian metric,
*
exponential map (Lie theory)
In the theory of Lie groups, the exponential map is a map from the Lie algebra \mathfrak g of a Lie group G to the group, which allows one to recapture the local group structure from the Lie algebra. The existence of the exponential map is one of ...
from a Lie algebra to a Lie group,
* More generally, in a manifold with an
affine connection
In differential geometry, an affine connection is a geometric object on a smooth manifold which ''connects'' nearby tangent spaces, so it permits tangent vector fields to be differentiated as if they were functions on the manifold with values ...
,
, where
is a
geodesic
In geometry, a geodesic () is a curve representing in some sense the shortest path ( arc) between two points in a surface, or more generally in a Riemannian manifold. The term also has meaning in any differentiable manifold with a connection. ...
with initial velocity ''X'', is sometimes also called the exponential map. The above two are special cases of this with respect to appropriate affine connections.
*
Euler's formula
Euler's formula, named after Leonhard Euler, is a mathematical formula in complex analysis that establishes the fundamental relationship between the trigonometric functions and the complex exponential function. Euler's formula states that for ...
forming the unit circle in the complex plane.
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