Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Randomness and collectivity in nuclear structure: Three theoretical
  puzzles   We show and interpret three examples of nontrivial results obtained in
numerical simulations of many-body systems: exponential convergence of
low-lying energy eigenvalues in the process of progressive truncation of huge
shell-model matrices, apparently ordered spectra generated by random
interactions, and regular behavior of complex many-body energies in a system
with single-particle orbitals in continuum. The possible practical applications
and new approaches are suggested.

35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph