Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Classification of head-on collisions of ion-acoustic solitary waves in a
  plasma with cold ions and Boltzmann elecrons
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat