Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Integral transform approach to solving Klein-Gordon equation with
  variable coefficients   In this paper we describe the integral transform that allows to write
solutions of one partial differential equation via solution of another one.
This transform was suggested by the author in the case when the last equation
is a wave equation, and then it was used to investigate several well-known
equations such as Tricomi-type equation, the Klein-Gordon equation in the
de~Sitter and Einstein-de~Sitter spacetimes. A generalization given in this
paper allows us to consider also the Klein-Gordon equations with coefficients
depending on the spatial variables.

35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org