Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Spectral and Energy Efficiency of Multi-pair Massive MIMO Relay Network
  with Hybrid Processing
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph