Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The importance of anisotropy for relativistic fluids with spherical
  symmetry   It is shown that an effective anisotropic spherically symmetric fluid model
with heat flow can absorb the addition to a perfect fluid of pressure
anisotropy, heat flow, bulk and shear viscosity, electric field and null fluid.
In most cases the induction of effective heat flow can be avoided.

18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
4
The categories of this paper are: cond-mat