Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: The Quasi-Linear Evolution of the Density Field in Models of
  Gravitational Instability
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph