Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A Statistical Study on Force-Freeness of Solar Magnetic Fields in the
  Photosphere
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys