Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Non-linearity of Vaidya spacetime and forces in the central naked
  singularity
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga