Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Approximation of the Double Travelling Salesman Problem with Multiple
  Stacks   The Double Travelling Salesman Problem with Multiple Stacks, DTSPMS, deals
with the collect and delivery of n commodities in two distinct cities, where
the pickup and the delivery tours are related by LIFO constraints. During the
pickup tour, commodities are loaded into a container of k rows, or stacks, with
capacity c. This paper focuses on computational aspects of the DTSPMS, which is
NP-hard.
  We first review the complexity of two critical subproblems: deciding whether
a given pair of pickup and delivery tours is feasible and, given a loading
plan, finding an optimal pair of pickup and delivery tours, are both polynomial
under some conditions on k and c.
  We then prove a (3k)/2 standard approximation for the MinMetrickDTSPMS, where
k is a universal constant, and other approximation results for various versions
of the problem.
  We finally present a matching-based heuristic for the 2DTSPMS, which is a
special case with k=2 rows, when the distances are symmetric. This yields a
1/2-o(1), 3/4-o(1) and 3/2+o(1) standard approximation for respectively
Max2DTSPMS, its restriction Max2DTSPMS-(1,2) with distances 1 and 2, and
Min2DTSPMS-(1,2), and a 1/2-o(1) differential approximation for Min2DTSPMS and
Max2DTSPMS.

35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: econ
9
The categories of this paper are: nlin
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The categories of this paper are: comp-gas
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The categories of this paper are: quant-ph
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: nucl-th