Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exact solution of the hydrodynamical Riemann problem with nonzero
  tangential velocities and the ultrarelativistic equation of state   We give a solution of the Riemann problem in relativistic hydrodynamics in
the case of ultrarelativistic equation of state and nonvanishing components of
the velocity tangent to the initial discontinuity. Simplicity of the
ultra-relativistic equation of state (the pressure being directly proportional
to the energy density) allows us to express this solution in analytical terms.
The result can be used both to construct and test numerical schemes for
relativistic Euler equations in (3 + 1) dimensions.

11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph