Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the regularity of solutions to the equation - \Delta u + b \nabla u =
  0   We consider the equation - \Delta u + b \nabla u = 0. The dependence of the
local regularity of a solution on the properties of the coefficient b is
investigated.

36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph