Marco Cesati, Luca Trevisan

A polynomial time approximation scheme (PTAS) for an optimization

problem $A$ is an algorithm that on input an instance of $A$ and

$\epsilon > 0$ finds a $(1+\epsilon)$-approximate solution in time

that is polynomial for each fixed $\epsilon$. Typical running times

are $n^{O(1/\epsilon)}$ or $2^{1/\epsilon^{O(1)}} ...
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Marco Cesati, Miriam Di Ianni

We consider the framework of Parameterized Complexity, and we

investigate the issue of which problems do admit efficient fixed

parameter parallel algorithms by introducing two different

degrees of efficiently parallelizable parameterized problems, PNC

and FPP. We sketch both some FPP-algorithms solving natural

parameterized problems and ...
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Marco Cesati

We show that the parameterized problem Perfect Code belongs to W[1].

This result closes an old open question, because it was often

conjectured that Perfect Code could be a natural problem having

complexity degree intermediate between W[1] and W[2]. This result

also shows W[1]-membership of the parameterized problem Weighted

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Jochen Alber, Henning Fernau, Rolf Niedermeier

A parameterized problem is called fixed parameter tractable

if it admits a solving algorithm whose running time on

input instance $(I,k)$ is $f(k) \cdot |I|^\alpha$, where $f$

is an arbitrary function depending only on~$k$. Typically,

$f$ is some exponential function, e.g., $f(k)=c^k$ for ...
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Henning Fernau

We derive the first lower bound results on kernel sizes of parameterized problems. The same idea also allows us to sometimes "de-parameterize"

parameterized algorithms.

Yijia Chen, Martin Grohe

We establish a close connection between (sub)exponential time complexity and parameterized complexity by proving that the so-called miniaturization mapping is a reduction preserving isomorphism between the two theories.

more >>>Henning Fernau

We are going to analyze simple search tree algorithms

for Weighted d-Hitting Set. Although the algorithms are simple, their analysis is technically rather involved. However, this approach allows us to even improve on elsewhere published algorithm running time estimates for the more restricted case of (unweighted) d-Hitting Set.

Stefan S. Dantchev, Barnaby Martin, Stefan Szeider

We propose a proof-theoretic approach for gaining evidence that certain parameterized problems are not fixed-parameter tractable. We consider proofs that witness that a given propositional formula cannot be satisfied by a truth assignment that sets at most k variables to true, considering k as the parameter. One could separate the ... more >>>

Martin Grohe

Algorithmic meta theorems are algorithmic results that apply to whole families of combinatorial problems, instead of just specific problems. These families are usually defined in terms of logic and graph theory. An archetypal algorithmic meta theorem is Courcelle's Theorem, which states that all graph properties definable in monadic second-order logic ... more >>>

Yijia Chen, Martin Grohe, Magdalena Grüber

Combining classical approximability questions with parameterized complexity, we introduce a theory of parameterized approximability.

The main intention of this theory is to deal with the efficient approximation of small cost solutions for optimisation problems.

Yijia Chen, Jörg Flum, Moritz Müller

Among others, refining the methods of [Fortnow and Santhanam, ECCC Report TR07-096] we improve a result of this paper and show for any parameterized problem with a ``linear weak OR'' and with NP-hard underlying classical problem that there is no polynomial reduction from the problem to itself that assigns to ... more >>>

Müller Moritz

We show analogues of a theorem due to Valiant and Vazirani

for intractable parameterized complexity classes such as W[P], W[SAT]

and the classes of the W-hierarchy as well as those of the A-hierarchy.

We do so by proving a general ``logical'' version of it which may be of

independent interest

Yijia Chen, Jörg Flum

In [Blass, Gurevich, and Shelah, 99] a logic L_Y has been introduced as a possible candidate for a logic capturing the PTIME properties of structures (even in the absence of an ordering of their universe). A reformulation of this problem in terms of a parameterized halting problem p-Acc for nondeterministic ... more >>>

Stephan Kreutzer, Anuj Dawar

We show that if $\mathcal C$ is a class of graphs which is

"nowhere dense" then first-order model-checking is

fixed-parameter tractable on $\mathcal C$. As all graph classes which exclude a fixed minor, or are of bounded local tree-width or locally exclude a minor are nowhere dense, this generalises algorithmic ...
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Stephan Kreutzer

Algorithmic meta-theorems are general algorithmic results applying to a whole range of problems, rather than just to a single problem alone. They often have a logical and a

structural component, that is they are results of the form:

"every computational problem that can be formalised in a given logic L ...
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Dieter van Melkebeek, Holger Dell

Consider the following two-player communication process to decide a language $L$: The first player holds the entire input $x$ but is polynomially bounded; the second player is computationally unbounded but does not know any part of $x$; their goal is to cooperatively decide whether $x$ belongs to $L$ at small ... more >>>

Olaf Beyersdorff, Nicola Galesi, Massimo Lauria

Parameterized Resolution and, moreover, a general framework for parameterized proof complexity was introduced by Dantchev, Martin, and Szeider (FOCS'07). In that paper, Dantchev et al. show a complexity gap in tree-like Parameterized Resolution for propositional formulas arising from translations of first-order principles.

We broadly investigate Parameterized Resolution obtaining the following ...
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Olaf Beyersdorff, Nicola Galesi, Massimo Lauria, Alexander Razborov

A general framework for parameterized proof complexity was introduced by Dantchev, Martin, and Szeider (FOCS'07). In that framework the parameterized version of any proof system is not fpt-bounded for some technical reasons, but we remark that this question becomes much more interesting if we restrict ourselves to those parameterized contradictions ... more >>>

Serge Gaspers, Stefan Szeider

We investigate the parameterized complexity of deciding whether a constraint network is $k$-consistent. We show that, parameterized by $k$, the problem is complete for the complexity class co-W[2]. As secondary parameters we consider the maximum domain size $d$ and the maximum number $\ell$ of constraints in which a variable occurs. ... more >>>

Danny Hermelin, Xi Wu

We introduce a new form of composition called \emph{weak composition} that allows us to obtain polynomial kernelization lower-bounds for several natural parameterized problems. Let $d \ge 2$ be some constant and let $L_1, L_2 \subseteq \{0,1\}^* \times \N$ be two parameterized problems where the unparameterized version of $L_1$ is \NP-hard. ... more >>>

Janka Chlebíková, Morgan Chopin

We consider the complexity of the firefighter problem where ${b \geq 1}$ firefighters are available at each time step. This problem is proved NP-complete even on trees of degree at most three and budget one (Finbow et al. 2007) and on trees of bounded degree $b+3$ for any fixed budget ... more >>>

Hasan Abasi, Nader Bshouty, Ariel Gabizon, Elad Haramaty

An $r$-simple $k$-path is a {path} in the graph of length $k$ that

passes through each vertex at most $r$ times. The \simpath{r}{k}

problem, given a graph $G$ as input, asks whether there exists an

$r$-simple $k$-path in $G$. We first show that this problem is

NP-Complete. We then show ...
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Holger Dell

Drucker (2012) proved the following result: Unless the unlikely complexity-theoretic collapse coNP is in NP/poly occurs, there is no AND-compression for SAT. The result has implications for the compressibility and kernelizability of a whole range of NP-complete parameterized problems. We present a simple proof of this result.

An AND-compression is ... more >>>

Vikraman Arvind, Sebastian Kuhnert, Johannes Köbler, Jacobo Toran

Given a system of linear equations $Ax=b$ over the binary field $\mathbb{F}_2$ and an integer $t\ge 1$, we study the following three algorithmic problems:

1. Does $Ax=b$ have a solution of weight at most $t$?

2. Does $Ax=b$ have a solution of weight exactly $t$?

3. Does $Ax=b$ have a ...
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Rahul Mehta

We prove that a variant of 2048, a popular online puzzle game, is PSPACE-Complete. Our hardness result

holds for a version of the problem where the player has oracle access to the computer player's moves.

Specifically, we show that for an $n \times n$ game board $G$, computing a

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Martin Lück, Arne Meier, Irina Schindler

We present a complete classification of the parameterized complexity of all operator fragments of the satisfiability problem in computation tree logic CTL. The investigated parameterization is temporal depth and pathwidth. Our results show a dichotomy between W[1]-hard and fixed-parameter tractable fragments. The two real operator fragments which are in FPT ... more >>>

Subhash Khot, Igor Shinkar

In the $Gap-clique(k, \frac{k}{2})$ problem, the input is an $n$-vertex graph $G$, and the goal is to decide whether $G$ contains a clique of size $k$ or contains no clique of size $\frac{k}{2}$. It is an open question in the study of fixed parameterized tractability whether the $Gap-clique(k, \frac{k}{2})$ problem ... more >>>

Ronald de Haan

We consider several non-uniform variants of parameterized complexity classes that have been considered in the literature. We do so in a homogenous notation, allowing a clear comparison of the various variants. Additionally, we consider some novel (non-uniform) parameterized complexity classes that come up in the framework of parameterized knowledge compilation. ... more >>>

Vikraman Arvind, Johannes Köbler, Sebastian Kuhnert, Jacobo Toran

We consider the PermCode problem to decide, given a representation of a permutation group G and a parameter k, whether there is a non-trivial element of G with support at most k. This problem generalizes several problems in the literature. We introduce a new method that allows to reduce the ... more >>>

Karthik C. S., Bundit Laekhanukit, Pasin Manurangsi

We study the parameterized complexity of approximating the $k$-Dominating Set (domset) problem where an integer $k$ and a graph $G$ on $n$ vertices are given as input, and the goal is to find a dominating set of size at most $F(k) \cdot k$ whenever the graph $G$ has a dominating ... more >>>