Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Unidirectional reflectionlessness and invisibility in the TE and TM
  modes of a PT-symmetric slab system
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat