Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Group Analysis of Nonlinear Internal Waves in Oceans. I:
  Self-adjointness, conservation laws, invariant solutions   The paper is devoted to the group analysis of equations of motion of
two-dimensional uniformly stratified rotating fluids used as a basic model in
geophysical fluid dynamics. It is shown that the nonlinear equations in
question have a remarkable property to be self-adjoint.
  This property is crucial for constructing conservation laws provided in the
present paper. Invariant solutions are constructed using certain symmetries.
The invariant solutions are used for defining internal wave beams.

29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph