Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Two-Stage Subspace Constrained Precoding in Massive MIMO Cellular
  Systems
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat