Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On a class of non-self-adjoint periodic eigenproblems with boundary and
  interior singularities   We prove that the spectrum of a certain PT-symmetric periodic problem is
purely real. Our results extend to a larger class of potentials those recently
found by Brian Davies [math.SP/0702122] and John Weir [arXiv:0711.1371].

4
The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph