Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lagrangian reduction of nonholonomic discrete mechanical systems by
  stages   In this work we introduce a category $LDP_d$ of discrete-time dynamical
systems, that we call discrete Lagrange--D'Alembert--Poincar\'e systems, and
study some of its elementary properties. Examples of objects of $LDP_d$ are
nonholonomic discrete mechanical systems as well as their lagrangian reductions
and, also, discrete Lagrange-Poincar\'e systems. We also introduce a notion of
symmetry group for objects of $LDP_d$ and a process of reduction when
symmetries are present. This reduction process extends the reduction process of
discrete Lagrange--Poincar\'e systems as well as the one defined for
nonholonomic discrete mechanical systems. In addition, we prove that, under
some conditions, the two-stage reduction process (first by a closed and normal
subgroup of the symmetry group and, then, by the residual symmetry group)
produces a system that is isomorphic in $LDP_d$ to the system obtained by a
one-stage reduction by the full symmetry group.

21
The categories of this paper are: adap-org
26
The categories of this paper are: bayes-an
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The categories of this paper are: eess
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th