Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generalised energy conservation law for the wave equations with variable
  propagation speed   We investigate the long time behaviour of the $L^2$-energy of solutions to
wave equations with variable speed. The novelty of the approach is the
combination of estimates for higher order derivatives of the coefficient with a
stabilisation property.

15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
3
The categories of this paper are: physics
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat