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Sobolev type norms and basis functions

  1. Jan 26, 2012 #1
    Hello everybody,

    I am given a "Sobolev type innerproduct"

    [itex]\langle f,g \rangle_{\alpha} = \langle f,g \rangle_{L^2} + \alpha \langle Rf,Rg \rangle_{L^2}[/itex]

    for some [itex]\alpha \geq 0[/itex] and [itex]R[/itex] some differential operator (e.g. the second-derivative operator).

    My question is now whether a function space endowed with such an inner-product can be a Hilbert space?

    Also I wonder whether there exists an analogue to the spectral theorem for compact and self-adjoint operators on Hilbert spaces also in Sobolev spaces?

    Thanks for any input on these questions!
  2. jcsd
  3. Jan 28, 2012 #2
    I figured it out!

    I showed that the norm induced by [itex]\langle \cdot, \cdot \rangle_{\alpha}[/itex] is indeed equivalent to the standard Sobolev norm [itex] \Vert \cdot \Vert_{W^{2,2}}[/itex] of the Sobolev space [itex] W^{2,2} [/itex] which is of course the (reproducing kernel) Hilbert space [itex] H^2 [/itex].
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