Talk:Lagrangian

From Wikipedia, the free encyclopedia

Physics Portal

This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.

Start

This article has been rated as start-Class on the assessment scale.

High

This article is on a subject of high importance within physics.

Help with this template

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

Can someone please explain where $\partial_\mu$ came from? -- Taral 17:38, 17 Jun 2004 (UTC)

$\partial_\mu$ (shorthand for $\frac {\partial}{\partial x^\mu}$ ) crops up here instead of $\frac{d}{dt}$ that you see in, for example action, because the function that is being varied, $\ \phi(x)$ is a function of 'n' variables

x μ

(

μ

= 1,2,3 ... n) as opposed to q(t) which is a function of 1 variable t. -- Amar 10:03, Jun 18, 2004 (UTC)

Lagrangian, Lagrangian mechanics and Action (physics) all contain duplicate material! Phys 19:00, 24 Jul 2004 (UTC)

Agree. Will try and attempt a merge sometime soon. [[User:AmarChandra|Amar | Talk]] 09:14, Jul 28, 2004 (UTC)

If no one objects, I'll add the content of this page to Lagrangian mechanics and set up a redirect here. - mako 30 June 2005 00:19 (UTC)

Can someone explain why is the spelling "Lagrangian" preferred here to "Lagrangean"? I would expect the pattern "Shakespeare -> Shakespearean".

I would suspect the difference is time period. Shakespeare -> Shakespearean was probably a valid English formation for a significant period of time. Lagrange lived more recently by ~200 years, when Lagrange -> Lagrangian was probably favored.

Personally, I had never even considered "Lagrangean" as an option, but apparently it is sometimes used: Google search turns up 1:27 for Lagrangean:Lagrangian. --Laura Scudder 16:54, 3 Apr 2005 (UTC)

Isn't it because Lagrangean is pronounced with a hard g, so to keep the soft j sound it's spelled Lagrangian? Fephisto 17:19, 30 December 2006 (UTC)

[edit] Functional

Is the Lagrangian itself a functional? It doesn't seem to be by the definition given. It's the expression for the action that's a functional, mapping a set of functions onto R. It's true that the coordinates that are the domain of the Lagrangian can be expressed as funtions of some parameter, but I'm not sure if that really makes the Lagrangian a functional; it certainly seems to be a differant case from the action integral.

I'm not confident enough to change this, and there do seem to be multiple definitions of functional, which confuses things. Comments? --Starwed 14:42, 14 December 2005 (UTC)

By the only definition of functional I know, it is indeed the action, not the Lagrangian that is a functional. I'll be bold and see if anyone comes up with another definition. — Laura Scudder ☎ 15:23, 14 December 2005 (UTC)

[edit] Vote for new external link

Here's my site full of PDE's with harmonic functions. Someone please put it in the external links if you think it's helpful!

http://www.exampleproblems.com/wiki/index.php/Calculus_of_Variations

[edit] Conflict of interest

Like User:Linas, I am concerned about recent edits by the data.optics.arizona.edu anon of this and other articles, edits which present the work of B Roy Frieden as mainstream. In fact, this work is not universally accepted and has been severely criticized (google for sci.physics.research discussion from some years ago, for starters). The conflict of interest is that this anon has confessed to being B. Roy Frieden IRL:

Notable edits by the data.optics.arizona.edu anon include:

150.135.248.180 (talk • contribs)
1. 20 May 2005 confesses to being Roy Frieden in real life
2. 6 June 2006: adds cites of his papers to Extreme physical information
3. 23 May 2006 adds uncritical description of his own work in Lagrangian and uncritically cites his own controversial book
4. 22 October 2004 attributes uncertainty principle to Cramer-Rao inequality, which is potentially misleading
5. 21 October 2004 adds uncritical mention of his controversial claim that Maxwell-Boltzmann distribution can be obtained via his "method"
6. 21 October 2004 adds uncritical mention of his controversial claim that the Klein-Gordon equation can be "derived" via his "method"
150.135.248.126 (talk • contribs)
1. 9 September 2004 adds uncritical description of his work to Fisher information
2. 8 September 2004 adds uncritical description of his highly dubious claim that EPI is a general approach to physics to Physical information
3. 16 August 2004 confesses IRL identity
4. 13 August 2004 creates uncritical account of his work in new article, Extreme physical information