Are Euler-Lagrange Equations Applicable to All Differential Manifolds?

In summary, the conversation discusses the applicability of Lagrange's equations in different types of manifolds. It is determined that they work for pseudo-riemann manifolds in general relativity, and also for other types of manifolds as long as they have local coordinate systems. The geometry of the manifold only plays a role if it affects the Lagrangian.
  • #1
Incand
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Hey!
I'm not sure if this belongs better here or in mechanics but while I was doing some mechanics problems I started wondering if Lagrange equations are true for any differential manifold.
Obviously they work for pseudo-riemann ones (general relativity) but do they work for others (all)?

I got no real knowledge of the math behind at all just wondered, since they work for relativistic particles, in what geometry they do and don't work.
 
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  • #2
Lagrange's equations are a local thing, so yes, because locally, in a manifold, it's no different from R^n. Actually, the configuration spaces you see in mechanics tend to be manifolds, so you're presumably already using the fact that they work in manifolds. You don't necessarily care about the geometry, unless that feeds into the Lagrangian somehow (generally, it will, but not always). It all just depends on having local coordinate systems, and that precedes the geometry.
 
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  • #3
Thanks, very well explained!
 

1. What are Euler-Lagrange equations?

Euler-Lagrange equations are a set of differential equations used to determine the critical points of a given functional, which is a mathematical function that takes in a set of functions as inputs and outputs a single number. They are commonly used in the field of calculus of variations to solve optimization problems.

2. How are Euler-Lagrange equations derived?

Euler-Lagrange equations are derived using the calculus of variations, which involves finding the stationary points of a functional by varying the functions that are inputs to the functional. This variation leads to a set of differential equations, known as the Euler-Lagrange equations, which can then be solved to find the critical points of the functional.

3. What is the significance of Euler-Lagrange equations?

Euler-Lagrange equations are significant because they allow us to find the extreme values of a functional, which can then be used to optimize various physical systems. They have applications in various fields such as physics, engineering, and economics.

4. Can Euler-Lagrange equations be used for both single and multi-variable functions?

Yes, Euler-Lagrange equations can be used for both single and multi-variable functions. In the case of a single-variable function, the Euler-Lagrange equation reduces to the classical calculus derivative formula. However, for multi-variable functions, the equations become more complex and involve partial derivatives.

5. Are there any limitations to using Euler-Lagrange equations?

While Euler-Lagrange equations are powerful tools for solving optimization problems, they do have some limitations. They can only be used for continuous and differentiable functions, and they may not always provide a unique solution. Additionally, the calculations involved in solving the equations can be complex and time-consuming for more complicated functions.

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