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Question about variational derivative

  1. Jun 29, 2012 #1
    I have a question as to what notation should I use for the following derivation ( I have no background on calculus of variation ):

    In linear media , the stored energy in a given volume is given by


    Now intuitively

    1) [itex]H=\frac{d W_{mag}}{dv d B}[/itex]

    But this is not the way they write it, instead one of the following notations are used:

    2) [itex]H=\frac{\partial W_{mag}}{\partial B}[/itex]
    3) [itex]H=\frac{\delta W_{mag}}{\delta B}[/itex] ( dv is missing)

    What is the right notation for equation 1 ?


    Edit: In 1) it is assumed that B inside the infinitesimal volume (dv) changes to B+dB while outside dv it remained constant.
    Last edited: Jun 29, 2012
  2. jcsd
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