Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Weak periodic solutions of $x\ddot{x} + 1 = 0$ and the harmonic balance
  method
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin