Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generating potentials via difference equations   The condition for pressure isotropy, for spherically symmetric gravitational
fields with charged and uncharged matter, is reduced to a recurrence equation
with variable, rational coefficients. This difference equation is solved in
general using mathematical induction leading to an exact solution to the
Einstein field equations which extends the isotropic model of John and Maharaj.
The metric functions, energy density and pressure are well behaved which
suggests that this model could be used to describe a relativistic sphere. The
model admits a barotropic equation of state which approximates a polytrope
close to the stellar centre.

29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess