Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sign-indefinite second order differential operators on finite metric
  graphs   The question of self-adjoint realizations of sign-indefinite second order
differential operators is discussed in terms of a model problem. Operators of
the type $-\frac{d}{dx} \sgn (x) \frac{d}{dx}$ are generalized to finite, not
necessarily compact, metric graphs. All self-adjoint realizations are
parametrized using methods from extension theory. The spectral and scattering
theory of the self-adjoint realizations are studied in detail.

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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
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The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph