Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Filling-Control Metal-Insulator Transition in the Hubbard Model Studied
  by the Operator Projection Method
28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex