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Homework Help: Closed form?

  1. Jul 19, 2005 #1
    closed form??

    let [tex] f:u \rightarrow R^n [/tex] be a differentiable function with a differentiable inverse [tex] f^{-1}: f(u) \rightarrow R^n [/tex]. if every closed form on u is exact, show that the same is true for f(u).

    Hint: if dw=0 and [tex]f^{\star}w = d\eta, [/tex] consider [tex](f^{-1})^{\star}\eta. [/tex]

    i don't know where to start with the problem. what is a closed form? what does it mean that "every closed form on u is exact"?
  2. jcsd
  3. Jul 19, 2005 #2


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    Science Advisor

    Well, where did you get the problem? I can't believe that wherever you got the problem (class or text) didn't have a definition of "closed" and "exact" form!

    A differential form ω is closed if dω= 0, exact if ω= dφ for some differential form φ. It can be shown that d(dφ)= 0 for any differential form φ so if ω is exact then dω= d(d&phi)= 0.

    One question you didn't ask: what is [tex]f^{\star}[/tex]?
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