18,959 research outputs found
Algorithms on Minimizing the Maximum Sensor Movement for Barrier Coverage of a Linear Domain
In this paper, we study the problem of moving sensors on a line to form a
barrier coverage of a specified segment of the line such that the maximum
moving distance of the sensors is minimized. Previously, it was an open
question whether this problem on sensors with arbitrary sensing ranges is
solvable in polynomial time. We settle this open question positively by giving
an time algorithm. For the special case when all sensors have
the same-size sensing range, the previously best solution takes time.
We present an time algorithm for this case; further, if all
sensors are initially located on the coverage segment, our algorithm takes
time. Also, we extend our techniques to the cycle version of the problem
where the barrier coverage is for a simple cycle and the sensors are allowed to
move only along the cycle. For sensors with the same-size sensing range, we
solve the cycle version in time, improving the previously best
time solution.Comment: This version corrected an error in the proof of Lemma 2 in the
previous version and the version published in DCG 2013. Lemma 2 is for
proving the correctness of an algorithm (see the footnote of Page 9 for why
the previous proof is incorrect). Everything else of the paper does not
change. All algorithms in the paper are exactly the same as before and their
time complexities do not change eithe
DynamO: A free O(N) general event-driven molecular-dynamics simulator
Molecular-dynamics algorithms for systems of particles interacting through
discrete or "hard" potentials are fundamentally different to the methods for
continuous or "soft" potential systems. Although many software packages have
been developed for continuous potential systems, software for discrete
potential systems based on event-driven algorithms are relatively scarce and
specialized. We present DynamO, a general event-driven simulation package which
displays the optimal O(N) asymptotic scaling of the computational cost with the
number of particles N, rather than the O(N log(N)) scaling found in most
standard algorithms. DynamO provides reference implementations of the best
available event-driven algorithms. These techniques allow the rapid simulation
of both complex and large (>10^6 particles) systems for long times. The
performance of the program is benchmarked for elastic hard sphere systems,
homogeneous cooling and sheared inelastic hard spheres, and equilibrium
Lennard-Jones fluids. This software and its documentation are distributed under
the GNU General Public license and can be freely downloaded from
http://marcusbannerman.co.uk/dynamo
Interning Ground Terms in XSB
This paper presents an implementation of interning of ground terms in the XSB
Tabled Prolog system. This is related to the idea of hash-consing. I describe
the concept of interning atoms and discuss the issues around interning ground
structured terms, motivating why tabling Prolog systems may change the
cost-benefit tradeoffs from those of traditional Prolog systems. I describe the
details of the implementation of interning ground terms in the XSB Tabled
Prolog System and show some of its performance properties. This implementation
achieves the effects of that of Zhou and Have but is tuned for XSB's
representations and is arguably simpler.Comment: Proceedings of the 13th International Colloquium on Implementation of
Constraint LOgic Programming Systems (CICLOPS 2013), Istanbul, Turkey, August
25, 201
Look before you Hop: Conversational Question Answering over Knowledge Graphs Using Judicious Context Expansion
Fact-centric information needs are rarely one-shot; users typically ask follow-up questions to explore a topic. In such a conversational setting, the user's inputs are often incomplete, with entities or predicates left out, and ungrammatical phrases. This poses a huge challenge to question answering (QA) systems that typically rely on cues in full-fledged interrogative sentences. As a solution, we develop CONVEX: an unsupervised method that can answer incomplete questions over a knowledge graph (KG) by maintaining conversation context using entities and predicates seen so far and automatically inferring missing or ambiguous pieces for follow-up questions. The core of our method is a graph exploration algorithm that judiciously expands a frontier to find candidate answers for the current question. To evaluate CONVEX, we release ConvQuestions, a crowdsourced benchmark with 11,200 distinct conversations from five different domains. We show that CONVEX: (i) adds conversational support to any stand-alone QA system, and (ii) outperforms state-of-the-art baselines and question completion strategies
Two Decades of Maude
This paper is a tribute to José Meseguer, from the rest of us in the Maude team, reviewing the past, the present, and the future of the language and system with which we have been working for around two decades under his leadership. After reviewing the origins and the language's main features, we present the latest additions to the language and some features currently under development. This paper is not an introduction to Maude, and some familiarity with it and with rewriting logic are indeed assumed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Best-first heuristic search for multicore machines
To harness modern multicore processors, it is imperative to develop parallel versions of fundamental algorithms. In this paper, we compare different approaches to parallel best-first search in a shared-memory setting. We present a new method, PBNF, that uses abstraction to partition the state space and to detect duplicate states without requiring frequent locking. PBNF allows speculative expansions when necessary to keep threads busy. We identify and fix potential livelock conditions in our approach, proving its correctness using temporal logic. Our approach is general, allowing it to extend easily to suboptimal and anytime heuristic search. In an empirical comparison on STRIPS planning, grid pathfinding, and sliding tile puzzle problems using 8-core machines, we show that A*, weighted A* and Anytime weighted A* implemented using PBNF yield faster search than improved versions of previous parallel search proposals
A Stable Marriage Requires Communication
The Gale-Shapley algorithm for the Stable Marriage Problem is known to take
steps to find a stable marriage in the worst case, but only
steps in the average case (with women and men). In
1976, Knuth asked whether the worst-case running time can be improved in a
model of computation that does not require sequential access to the whole
input. A partial negative answer was given by Ng and Hirschberg, who showed
that queries are required in a model that allows certain natural
random-access queries to the participants' preferences. A significantly more
general - albeit slightly weaker - lower bound follows from Segal's general
analysis of communication complexity, namely that Boolean queries
are required in order to find a stable marriage, regardless of the set of
allowed Boolean queries.
Using a reduction to the communication complexity of the disjointness
problem, we give a far simpler, yet significantly more powerful argument
showing that Boolean queries of any type are indeed required for
finding a stable - or even an approximately stable - marriage. Notably, unlike
Segal's lower bound, our lower bound generalizes also to (A) randomized
algorithms, (B) allowing arbitrary separate preprocessing of the women's
preferences profile and of the men's preferences profile, (C) several variants
of the basic problem, such as whether a given pair is married in every/some
stable marriage, and (D) determining whether a proposed marriage is stable or
far from stable. In order to analyze "approximately stable" marriages, we
introduce the notion of "distance to stability" and provide an efficient
algorithm for its computation
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