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Jan 2, 2016 at 22:20 answer added jorge vargas timeline score: 1
S May 29, 2015 at 18:52 history edited Manny Reyes CC BY-SA 3.0
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S May 29, 2015 at 18:52 history suggested wdacda CC BY-SA 3.0
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May 27, 2015 at 19:32 answer added B K timeline score: 0
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Oct 11, 2014 at 12:00 history edited Wolfgang
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Apr 7, 2013 at 4:32 answer added Jonathan Gleason timeline score: 7
Mar 27, 2013 at 0:56 comment added Gateau au fromage You are perfectly right but I am thinking in physical term when you have an observable (self-adjoint linear diff. operator) whose "eigenvectors" generate the whole physical space (i.e. $L^2$). The eigenvectors corresponding to the continuous spectrum are unphysical but they can be added continuously in the form of an integral. In your example, there is only continuous spectrum but the Fourier series is a continuous sum over the unphysical solutions of the eigenvalue problem.
Mar 27, 2013 at 0:45 vote accept Gateau au fromage
S Mar 27, 2013 at 0:44 vote accept Gateau au fromage
Mar 27, 2013 at 0:45
Mar 27, 2013 at 0:44 vote accept Gateau au fromage
S Mar 27, 2013 at 0:44
Mar 26, 2013 at 23:44 vote accept Gateau au fromage
Mar 27, 2013 at 0:44
S Mar 26, 2013 at 23:42 vote accept Gateau au fromage
Mar 26, 2013 at 23:44
S Mar 26, 2013 at 23:42 vote accept Gateau au fromage
S Mar 26, 2013 at 23:42
Mar 26, 2013 at 23:41 vote accept Gateau au fromage
S Mar 26, 2013 at 23:42
Mar 26, 2013 at 23:41 vote accept Gateau au fromage
Mar 26, 2013 at 23:41
Mar 26, 2013 at 21:37 answer added user26107 timeline score: 5
Mar 26, 2013 at 20:21 comment added Aaron Hoffman To be concrete let's take $\partial_x^2$ defined on $H^2(\mathbb{R}) \subset L^2(\mathbb{R})$. What do you mean by eigenvectors? The solutions to the eigenvector equation $u_{xx} = \lambda u$ don't live in $L^2$. If we think of an orthonormal system of eigenvectors as forming the columns of an orthogonal matrix which diagonalizes the operator, perhaps the appropriate generalization is to seek a unitary transformation (Fourier Transform) which conjugates the operator with multiplication (by $-k^2$).
Mar 26, 2013 at 20:18 answer added Igor Khavkine timeline score: 11
Mar 26, 2013 at 20:16 comment added András Bátkai Weidmann's book is an excellent reference on the questions you mention. books.google.hu/books/about/…
Mar 26, 2013 at 19:55 history asked Gateau au fromage CC BY-SA 3.0