Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Oscillatory instability and routes to chaos in Rayleigh-B\'enard
  convection: effect of external magnetic field
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga