Is it worth learning Calculus of Variations?

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Discussion Overview

The discussion revolves around the value of learning calculus of variations, particularly in relation to its applications in physics and mathematics. Participants explore its theoretical foundations, connections to Lagrangian mechanics, and specific problems that can be addressed using this mathematical framework.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the necessity of studying calculus of variations if it primarily involves solving Euler-Lagrange equations.
  • Another participant argues that calculus of variations is the foundational concept from which Lagrangian and Hamiltonian mechanics arise, emphasizing its broader implications beyond just the Euler-Lagrange equations.
  • A different viewpoint highlights the aesthetic and practical significance of calculus of variations in solving complex problems in physics and engineering, citing examples like the brachistochrone problem.
  • One participant asserts that calculus of variations encompasses more than just the Euler-Lagrange equations, suggesting that it is worthwhile to understand its general principles, including applications like the derivation of Einstein's equations from the Einstein-Hilbert action.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between calculus of variations and Euler-Lagrange equations, with some asserting that the former is more general and foundational, while others question its necessity if it seems to reduce to the latter. The discussion remains unresolved regarding the overall value and scope of calculus of variations.

Contextual Notes

Participants mention specific applications and examples, but there is no consensus on the necessity or depth of understanding required for calculus of variations, indicating a range of assumptions and perspectives on its relevance.

torstum
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Hi everyone,

I'm already familiar with, and have used Lagrangians and Euler-Lagrange equations. I'm interested in calculus of variations, but if it all boils down to solving euler-lagrange equations (and this is probably the part where I'm mistaken), then what's the point? Please tell me if there is more to it than that. I would appreciate it.
 
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Er.. you have have this thing reversed. The calculus of variation, as far as I can tell, is the ORIGIN of Lagrangian/Hamiltonian mechanics. It is where the whole concept of a 'stationary'/maximal state and least-action principle are applied and expanded to the Lagrangian/Hamiltonian mechanics.

So no, they are not the same thing, even though they can lead to the same thing. Least action principle, for example, can account for Fermat's Least time principle. Besides, this would give you an analogous concept to the Feynman's path integral later on.

Zz.
 
To my mind, the calculus of variations is one of the most beautiful chapters in applied mathematics. There are a lot of problems in physics and engineering whose single solution requires knowledge of calculus of variations.

Think about the famous brahistochrone problem or the famous area-perimeter problems.
 
torstum said:
Hi everyone,

I'm already familiar with, and have used Lagrangians and Euler-Lagrange equations. I'm interested in calculus of variations, but if it all boils down to solving euler-lagrange equations (and this is probably the part where I'm mistaken), then what's the point? Please tell me if there is more to it than that. I would appreciate it.

Calculus of variation is much more general than the EL equations. So it is worthwhile to understand it. The point is that th evariables with respect to which one varies the actions are not necessarily simply a generalized position and its derivative.

As one example, you could look up the derivation of Einstein's equations from a variational principle applied to the Einstein-Hilbert action. There one varies with respect to the metric so things look quite different than the usual EL equations.
 
Thanks for the feedback, it sure looks like a beautiful theory, and well worth getting into.
 

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