Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasi-Hermiticity in infinite-dimensional Hilbert spaces   In infinite-dimensional Hilbert spaces, the application of the concept of
quasi-Hermiticity to the description of non-Hermitian Hamiltonians with real
spectra may lead to problems related to the definition of the metric operator.
We discuss these problems by examining some examples taken from the recent
literature and propose a formulation that is free of these difficulties.

20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg