Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hamiltonian description of vortex systems   In the framework of 2D ideal Hydrodynamics a vortex system is defined as a
smooth vorticity function having few positive local maxima and negative local
minima separated by curves of zero vorticity. Invariants of such structures are
discussed following from the vorticity conservation law and invertibility of
Lagrangian motion. Hamiltonian formalism for vortex systems is developed by
introducing new functional variables diagonalizing the original non-canonical
Poisson bracket.

33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
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The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys