Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A smoothing theory for open quantum systems: The least mean square
  approach   Unlike the classical smoothing theory, it is well known that quantum
smoothers are, in general, not well--defined by the quantum conditional
expectation. The purpose of this paper is to propose a new quantum smoothing
theory based on the least mean squared errors. The least mean square estimate
of quantum physical quantity composes from symmetric part and skew part, and we
developed the recursive equations, respectively.

37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
18
The categories of this paper are: econ