Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Triangle packing in (sparse) tournaments: approximation and
  kernelization   Given a tournament T and a positive integer k, the C_3-Pakcing-T problem asks
if there exists a least k (vertex-)disjoint directed 3-cycles in T. This is the
dual problem in tournaments of the classical minimal feedback vertex set
problem. Surprisingly C_3-Pakcing-T did not receive a lot of attention in the
literature. We show that it does not admit a PTAS unless P=NP, even if we
restrict the considered instances to sparse tournaments, that is tournaments
with a feedback arc set (FAS) being a matching. Focusing on sparse tournaments
we provide a (1+6/(c-1)) approximation algorithm for sparse tournaments having
a linear representation where all the backward arcs have "length" at least c.
Concerning kernelization, we show that C_3-Pakcing-T admits a kernel with O(m)
vertices, where m is the size of a given feedback arc set. In particular, we
derive a O(k) vertices kernel for C_3-Pakcing-T when restricted to sparse
instances. On the negative size, we show that C_3-Pakcing-T does not admit a
kernel of (total bit) size O(k^{2-\epsilon}) unless NP is a subset of coNP /
Poly. The existence of a kernel in O(k) vertices for C_3-Pakcing-T remains an
open question.

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The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
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The categories of this paper are: acc-phys