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Does being in C2 imply being in L2 for a function?

  1. Mar 22, 2013 #1
    Having bounded set ##U\subset\mathbb{R}^n## with ##C^1## boundary ##\partial U## and a function ##g\in C^2(\partial U)##, does one automatically have ##g\in L^2(\partial U)##?
    I don't need a proof/explanation, yes/no answer is sufficient.
     
  2. jcsd
  3. Mar 22, 2013 #2
    I assume ##C^2## is twice continuously differentiable and that ##L^2## square (Lebesgue)-integrable.

    The answer is no. An example is given by some modification of the function ##f(x)=\frac{\sin (x)}{x}##.

    If ##\partial U## is compact, then the answer is probably yes.
     
  4. Mar 22, 2013 #3

    mathman

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    Since the domain (U) is bounded, then your example is bad. U bounded and the condition on the boundary may be sufficient to insure continuity on the closure of U, which is compact.
     
  5. Mar 23, 2013 #4
    I somehow missed that ##U## was supposed to be bounded. The result is true then.
     
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