Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The matter Lagrangian of an ideal fluid   We show that the matter Lagrangian of an ideal fluid equals (up to a sign
-depending on its definition and on the chosen signature of the metric) the
total energy density of the fluid, i.e. rest energy density plus internal
energy density.

20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph