Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hydra Code Release   A revised version of Hydra, an adaptive particle-particle, particle-mesh plus
smoothed particle hydrodynamics code developed by; Hugh Couchman, University of
Western Ontario, Frazer Pearce, University of Durham, Peter Thomas, University
of Sussex, is now available as a tar file from;
http://coho.astro.uwo.ca/pub/hydra/hydra.html or
http://star-www.maps.susx.ac.uk/~pat/hydra/hydra.html .

12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat