Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational Collapse of a Massless Scalar Field and a Perfect Fluid
  with Self-Similarity of the First Kind in (2+1) Dimensions   Self-similar solutions of a collapsing perfect fluid and a massless scalar
field with kinematic self-similarity of the first kind in 2+1 dimensions are
obtained. Their local and global properties of the solutions are studied. It is
found that some of them represent gravitational collapse, in which black holes
are always formed, and some may be interpreted as representing cosmological
models.

35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph