Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Very basic partial derivatives problem

  1. Dec 29, 2009 #1
    I should feel ashamed to ask this, but it's giving me (and others) some troubles.

    given [tex]f(x_1,\ldots,x_n)[/tex], is it wrong to say that:

    [tex]\frac{\partial f}{\partial f}=1[/tex]

  2. jcsd
  3. Dec 29, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    It doesn't make a lot of sense... the idea is that in the expression [itex]\frac{\partial f}{\partial x}[/itex], f is a function and x is a variable on which f does (or does not, or does indirectly) depend.

    You can write
    [tex]\frac{\delta f(x_1, \cdots, x_n)}{\delta f(x_1', \cdots, x_n')} = \delta(x_1 - x_1') \cdots \delta(x_n - x_n')[/tex]
    where the delta's on the right hand side are Dirac delta distributions, but you are taking functional derivatives then.
  4. Dec 29, 2009 #3
    uhm...it makes some sense in the following context:
    however, there must be a mistake but I cannot see it.

    [EDIT]: in the thread mentioned above a solution to the problem is described in its correct context. Sorry for this kind of "double posting"; in the beginning I thought I was facing a different problem than the original.
    Last edited: Dec 30, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Very basic partial derivatives problem