Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonlinear dynamics of wave packets in PT-symmetric optical lattices near
  the phase transition point   Nonlinear dynamics of wave packets in PT-symmetric optical lattices near the
phase-transition point are analytically studied. A nonlinear Klein-Gordon
equation is derived for the envelope of these wave packets. A variety of novel
phenomena known to exist in this envelope equation are shown to also exist in
the full equation including wave blowup, periodic bound states and solitary
wave solutions.

25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con