Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Inverse Problem for the Euler-Poisson system in Cosmology   The motion of a continuum of matter subject to gravitational interaction is
classically described by the Euler-Poisson system. Prescribing the density of
matter at initial and final times, we are able to obtain weak solutions for
this equation by minimizing the action of the Lagrangian which is a convex
functional. Then we see that such minimizing solutions are consistent with
smooth solutions of the Euler-Poisson system and enjoy some special regularity
properties. Meanwhile some intersting links with with Hamilton-Jacobi equations
are found.

23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph