66 research outputs found
Satisfiability Parsimoniously Reduces to the Tantrix(TM) Rotation Puzzle Problem
Holzer and Holzer (Discrete Applied Mathematics 144(3):345--358, 2004) proved
that the Tantrix(TM) rotation puzzle problem is NP-complete. They also showed
that for infinite rotation puzzles, this problem becomes undecidable. We study
the counting version and the unique version of this problem. We prove that the
satisfiability problem parsimoniously reduces to the Tantrix(TM) rotation
puzzle problem. In particular, this reduction preserves the uniqueness of the
solution, which implies that the unique Tantrix(TM) rotation puzzle problem is
as hard as the unique satisfiability problem, and so is DP-complete under
polynomial-time randomized reductions, where DP is the second level of the
boolean hierarchy over NP.Comment: 19 pages, 16 figures, appears in the Proceedings of "Machines,
Computations and Universality" (MCU 2007
The Three-Color and Two-Color Tantrix(TM) Rotation Puzzle Problems are NP-Complete via Parsimonious Reductions
Holzer and Holzer (Discrete Applied Mathematics 144(3):345--358, 2004) proved
that the Tantrix(TM) rotation puzzle problem with four colors is NP-complete,
and they showed that the infinite variant of this problem is undecidable. In
this paper, we study the three-color and two-color Tantrix(TM) rotation puzzle
problems (3-TRP and 2-TRP) and their variants. Restricting the number of
allowed colors to three (respectively, to two) reduces the set of available
Tantrix(TM) tiles from 56 to 14 (respectively, to 8). We prove that 3-TRP and
2-TRP are NP-complete, which answers a question raised by Holzer and Holzer in
the affirmative. Since our reductions are parsimonious, it follows that the
problems Unique-3-TRP and Unique-2-TRP are DP-complete under randomized
reductions. We also show that the another-solution problems associated with
4-TRP, 3-TRP, and 2-TRP are NP-complete. Finally, we prove that the infinite
variants of 3-TRP and 2-TRP are undecidable.Comment: 30 pages, 25 figure
Acceptance in Incomplete Argumentation Frameworks
A Abstract argumentation frameworks (AFs), originally proposed by Dung, constitute a central formal model for the study of computational aspects of argumentation in AI. Credulous and skeptical acceptance of arguments in a given AF are well-studied problems both in terms of theoretical analysis-especially computational complexity-and the development of practical decision procedures for the problems. However, AFs make the assumption that all attacks between arguments are certain (i.e., present attacks are known to exist, and missing attacks are known to not exist), which can in various settings be a restrictive assumption. A generalization of AFs to incomplete AFs was recently proposed as a formalism that allows the representation of both uncertain attacks and uncertain arguments in AFs. In this article, we explore the impact of allowing for modeling such uncertainties in AFs on the computational complexity of natural generalizations of acceptance problems to incomplete AFs under various central AF semantics. Complementing the complexity-theoretic analysis, we also develop the first practical decision procedures for all of the NP-hard variants of acceptance in incomplete AFs. In terms of complexity analysis, we establish a full complexity landscape, showing that depending on the variant of acceptance and property/semantics, the complexity of acceptance in incomplete AFs ranges from polynomial-time decidable to completeness for Sigma(p)(3). In terms of algorithms, we show through an extensive empirical evaluation that an implementation of the proposed decision procedures, based on boolean satisfiability (SAT) solving, is effective in deciding variants of acceptance under uncertainties. We also establish conditions for what type of atomic changes are guaranteed to be redundant from the perspective of preserving extensions of completions of incomplete AFs, and show that the results allow for considerably improving the empirical efficiency of the proposed SAT-based counterexample-guided abstraction refinement algorithms for acceptance in incomplete AFs for problem variants with complexity beyond NP. (C) 2021 The Authors. Published by Elsevier B.V.Peer reviewe
Proposal for Quantum Simulation via All-Optically Generated Tensor Network States
We devise an all-optical scheme for the generation of entangled multimode
photonic states encoded in temporal modes of light. The scheme employs a
nonlinear down-conversion process in an optical loop to generate one- and
higher-dimensional tensor network states of light. We illustrate the principle
with the generation of two different classes of entangled tensor network states
and report on a variational algorithm to simulate the ground-state physics of
many-body systems. We demonstrate that state-of-the-art optical devices are
capable of determining the ground-state properties of the spin-1/2 Heisenberg
model. Finally, implementations of the scheme are demonstrated to be robust
against realistic losses and mode mismatch.Comment: 6 pages main text plus 6 pages Supplementary Material and many
figures. Updated to published version. Comments welcom
The Complexity of Computing Minimal Unidirectional Covering Sets
Given a binary dominance relation on a set of alternatives, a common thread
in the social sciences is to identify subsets of alternatives that satisfy
certain notions of stability. Examples can be found in areas as diverse as
voting theory, game theory, and argumentation theory. Brandt and Fischer [BF08]
proved that it is NP-hard to decide whether an alternative is contained in some
inclusion-minimal upward or downward covering set. For both problems, we raise
this lower bound to the Theta_{2}^{p} level of the polynomial hierarchy and
provide a Sigma_{2}^{p} upper bound. Relatedly, we show that a variety of other
natural problems regarding minimal or minimum-size covering sets are hard or
complete for either of NP, coNP, and Theta_{2}^{p}. An important consequence of
our results is that neither minimal upward nor minimal downward covering sets
(even when guaranteed to exist) can be computed in polynomial time unless P=NP.
This sharply contrasts with Brandt and Fischer's result that minimal
bidirectional covering sets (i.e., sets that are both minimal upward and
minimal downward covering sets) are polynomial-time computable.Comment: 27 pages, 7 figure
Processing of social and monetary rewards in autism spectrum disorders
Background: Reward processing has been proposed to underpin the atypical social feature of autism spectrum disorder (ASD). However, previous neuroimaging studies have yielded inconsistent results regarding the specificity of atypicalities for social reward processing in ASD.
Aims: Utilising a large sample, we aimed to assess reward processing in response to reward type (social, monetary) and reward phase (anticipation, delivery) in ASD.
Method: Functional magnetic resonance imaging during social and monetary reward anticipation and delivery was performed in 212 individuals with ASD (7.6-30.6 years of age) and 181 typically developing participants (7.6-30.8 years of age).
Results: Across social and monetary reward anticipation, whole-brain analyses showed hypoactivation of the right ventral striatum in participants with ASD compared with typically developing participants. Further, region of interest analysis across both reward types yielded ASD-related hypoactivation in both the left and right ventral striatum. Across delivery of social and monetary reward, hyperactivation of the ventral striatum in individuals with ASD did not survive correction for multiple comparisons. Dimensional analyses of autism and attention-deficit hyperactivity disorder (ADHD) scores were not significant. In categorical analyses, post hoc comparisons showed that ASD effects were most pronounced in participants with ASD without co-occurring ADHD.
Conclusions: Our results do not support current theories linking atypical social interaction in ASD to specific alterations in social reward processing. Instead, they point towards a generalised hypoactivity of ventral striatum in ASD during anticipation of both social and monetary rewards. We suggest this indicates attenuated reward seeking in ASD independent of social content and that elevated ADHD symptoms may attenuate altered reward seeking in ASD
- …