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What is a variation of the action?

  1. Dec 3, 2005 #1
    I dont have access to textbooks. The internet at present is pretty much my only source of information. I tried looking on the net but couldn't find anything pertaining to my questions.

    Ok so I have the expression for a Poincare invariant action. Then I have to find the variation of the action.

    What does the variation of the action mean? What is the basic formula for it, i.e the formula for the action was dS = L dt. What is the basic formula for the variation of the action? :cry:

    I tried looking on the net but couldn't find anything pertaining to my questions. I appreciate greatly what was given in my other thread on the same subject but I should have mentioned I was looking for the basics.

    Thankyou very much.
  2. jcsd
  3. Dec 4, 2005 #2


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    You have to specify the variables with which you wish to do the variations.
    (More specifically, you need to specify a configuration space and conditions upon which you vary a path.)

    Here's something to start you off
    http://mitpress.mit.edu/SICM/book-Z-H-12.html#%_sec_Temp_74 [Broken]

    Here's a resource that works out the Maxwell field http://www.plasma.uu.se/CED/Book/ (in "Covariant Field Theory")
    http://www.lorentz.leidenuniv.nl/vanbaal/FTcourse.html [Broken]
    http://xxx.lanl.gov/abs/hep-th/9912205 (probably more than you want)
    Last edited by a moderator: May 2, 2017
  4. Dec 4, 2005 #3
    Dear robphy,

    thank you =) some of the sorces you pointed out were exactly what I was looking for. Further it seems you have given me some very useful sources of online information for physics problems. Much appreciated.
    Last edited: Dec 4, 2005
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