Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Self-Organized Hydrodynamics with congestion and path formation in
  crowds
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat