How Is the Exponential Map Defined for Lie Groups Without a Metric?

In summary, the exponential map for Lie groups is equivalent to the exponential function. However, it is based on the geodesic ODE which requires a metric, which is not commonly given for Lie groups. This presents a challenge in obtaining the exponential map. Additionally, a connection, not necessarily the Levi-Civita connection, is needed for the geodesic ODE. Care must also be taken in defining the exponential map for a Lie group, as it involves a one-parameter subgroup with a given tangent vector.
  • #1
wacki
17
2
I’ve read about the exponential map that for Lie groups the exponential map is actually the exponential function. But the exponential map is based on the geodesic ODE, so you need Christoffel symbols and thus the metric. But usually nobody gives you a metric with a Lie group. So how can I get the exponential map (and finally see that it’s just the exponential function)?
 
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  • #2
wacki said:
But the exponential map is based on the geodesic ODE, so you need Christoffel symbols and thus the metric.
No you do not. You need a connection, not necessarily the Levi-Civita connection. In fact, asking for metric compatibility is senseless without a metric.
 
  • #3
Ahh yes, thanks Orodruin.
I clearly lack experience and intuition with non-Levi-Civita connections.
 
  • #4
You need to be careful when you say the exponential map. The exponential map for a Lie group is defined using the one parameter subgroup with a given tangent vector. For a manifold with a connection the geodesic is used.
 

FAQ: How Is the Exponential Map Defined for Lie Groups Without a Metric?

What is the exponential map for Lie groups?

The exponential map for Lie groups is a mathematical tool that maps elements of a Lie group (a type of mathematical group) to elements of its corresponding Lie algebra (a vector space associated with the group). It is a fundamental concept in the study of Lie groups and their applications in physics, engineering, and other fields.

How is the exponential map defined?

The exponential map is defined as a mapping from the tangent space of a Lie group at the identity element to the group itself. In other words, it takes a vector from the tangent space and "exponentiates" it to obtain an element of the group. The specific formula for the exponential map varies depending on the specific Lie group and its corresponding Lie algebra.

What is the significance of the exponential map in Lie group theory?

The exponential map plays a crucial role in Lie group theory as it allows for the translation of algebraic operations on the Lie algebra to the corresponding Lie group. This enables the study of Lie groups using tools and techniques from linear algebra and differential geometry.

What are some applications of the exponential map for Lie groups?

The exponential map has numerous applications in various fields of mathematics, physics, and engineering. It is used in the study of differential equations, dynamical systems, and optimization problems. It is also essential in the fields of robotics, computer graphics, and geometric modeling.

Are there any limitations or drawbacks of the exponential map for Lie groups?

While the exponential map is a powerful and useful tool, it is not without limitations. In some cases, the exponential map may not be well-defined, leading to difficulties in its application. Additionally, the computation of the exponential map can be computationally expensive, making it challenging to use in certain applications.

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