Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Matricial Range of $E_{21}$   The matricial range of the $2\times2$ matrix $E_{21}$ (i.e., the $2\times 2$
unilateral shift) is described very simply: it consists of all matrices with
numerical radius at most $1/2$. The known proofs of this simple statement,
however, are far from trivial and they depend on subtle results on dilations.
We offer here a brief introduction to the matricial range and a recap of those
two proofs, following independent work of Arveson and Ando in the early 1970s.

23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs