Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Exact diagonalisation study of charge order in the quarter-filled
  two-leg ladder system NaV2O5
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom