Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Regular reflection in self-similar potential flow and the sonic
  criterion   Reflection of a shock from a solid wedge is a classical problem in gas
dynamics. Depending on the parameters either a regular or a irregular
(Mach-type) reflection results. We construct regular reflection as an exact
self-similar solution for potential flow. For some upstream Mach numbers and
isentropic coefficients, a solution exists for all wedge angles allowed by the
sonic criterion. This demonstrates that, at least for potential flow, weaker
criteria are false.

21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin