942 research outputs found
On the Disambiguation of Weighted Automata
We present a disambiguation algorithm for weighted automata. The algorithm
admits two main stages: a pre-disambiguation stage followed by a transition
removal stage. We give a detailed description of the algorithm and the proof of
its correctness. The algorithm is not applicable to all weighted automata but
we prove sufficient conditions for its applicability in the case of the
tropical semiring by introducing the *weak twins property*. In particular, the
algorithm can be used with all acyclic weighted automata, relevant to
applications. While disambiguation can sometimes be achieved using
determinization, our disambiguation algorithm in some cases can return a result
that is exponentially smaller than any equivalent deterministic automaton. We
also present some empirical evidence of the space benefits of disambiguation
over determinization in speech recognition and machine translation
applications
Parallel Metric Tree Embedding based on an Algebraic View on Moore-Bellman-Ford
A \emph{metric tree embedding} of expected \emph{stretch~}
maps a weighted -node graph to a weighted tree with such that, for all ,
and
. Such embeddings are highly useful for designing
fast approximation algorithms, as many hard problems are easy to solve on tree
instances. However, to date the best parallel -depth algorithm that achieves an asymptotically optimal expected stretch of
requires
work and a metric as input.
In this paper, we show how to achieve the same guarantees using
depth and
work, where and is an arbitrarily small constant.
Moreover, one may further reduce the work to at the expense of increasing the expected stretch to
.
Our main tool in deriving these parallel algorithms is an algebraic
characterization of a generalization of the classic Moore-Bellman-Ford
algorithm. We consider this framework, which subsumes a variety of previous
"Moore-Bellman-Ford-like" algorithms, to be of independent interest and discuss
it in depth. In our tree embedding algorithm, we leverage it for providing
efficient query access to an approximate metric that allows sampling the tree
using depth and work.
We illustrate the generality and versatility of our techniques by various
examples and a number of additional results
Off-diagonal impedance in amorphous wires and application to linear magnetic sensors
The magnetic-field behaviour of the off-diagonal impedance in Co-based
amorphous wires is investigated under the condition of sinusoidal (50 MHz) and
pulsed (5 ns rising time) current excitations. For comparison, the field
characteristics of the diagonal impedance are measured as well. In general,
when an alternating current is applied to a magnetic wire the voltage signal is
generated not only across the wire but also in the coil mounted on it. These
voltages are related with the diagonal and off-diagonal impedances,
respectively. It is demonstrated that these impedances have a different
behaviour as a function of axial magnetic field: the former is symmetrical and
the latter is antisymmetrical with a near linear portion within a certain field
interval. In the case of the off-diagonal response, the dc bias current
eliminating circular domains is necessary. The pulsed excitation that combines
both high and low frequency harmonics produces the off-diagonal voltage
response without additional bias current or field. This suits ideal for a
practical sensor circuit design. The principles of operation of a linear
magnetic sensor based on C-MOS transistor circuit are discussed.Comment: Accepted to IEEE Trans. Magn. (2004
Feature weighting techniques for CBR in software effort estimation studies: A review and empirical evaluation
Context : Software effort estimation is one of the most important activities in the software development process. Unfortunately, estimates are often substantially wrong. Numerous estimation methods have been proposed including Case-based Reasoning (CBR). In order to improve CBR estimation accuracy, many researchers have proposed feature weighting techniques (FWT). Objective: Our purpose is to systematically review the empirical evidence to determine whether FWT leads to improved predictions. In addition we evaluate these techniques from the perspectives of (i) approach (ii) strengths and weaknesses (iii) performance and (iv) experimental evaluation approach including the data sets used. Method: We conducted a systematic literature review of published, refereed primary studies on FWT (2000-2014). Results: We identified 19 relevant primary studies. These reported a range of different techniques. 17 out of 19 make benchmark comparisons with standard CBR and 16 out of 17 studies report improved accuracy. Using a one-sample sign test this positive impact is significant (p = 0:0003). Conclusion: The actionable conclusion from this study is that our review of all relevant empirical evidence supports the use of FWTs and we recommend that researchers and practitioners give serious consideration to their adoption
Hybrid expansions for local structural relaxations
A model is constructed in which pair potentials are combined with the cluster
expansion method in order to better describe the energetics of structurally
relaxed substitutional alloys. The effect of structural relaxations away from
the ideal crystal positions, and the effect of ordering is described by
interatomic-distance dependent pair potentials, while more subtle
configurational aspects associated with correlations of three- and more sites
are described purely within the cluster expansion formalism. Implementation of
such a hybrid expansion in the context of the cluster variation method or Monte
Carlo method gives improved ability to model phase stability in alloys from
first-principles.Comment: 8 pages, 1 figur
Assessing the Positional Planimetric Accuracy of DBpedia Georeferenced Resources
International audienceAssessing the quality of the main linked data sources on the Web like DBpedia or Yago is an important research topic. The existing approaches for quality assessment mostly focus on determining whether data sources are compliant with Web of data best practices or on their completeness, semantic accuracy, consistency, relevancy or trustworthi-ness. In this article, we aim at assessing the accuracy of a particular type of information often associated with Web of data resources: direct spatial references. We present the approaches currently used for assessing the planimetric accuracy of geographic databases. We explain why they cannot be directly applied to the resources of the Web of data. Eventually , we propose an approach for assessing the planimetric accuracy of DBpedia resources, adapted to the open nature of this knowledge base
Reachability problems for products of matrices in semirings
We consider the following matrix reachability problem: given square
matrices with entries in a semiring, is there a product of these matrices which
attains a prescribed matrix? We define similarly the vector (resp. scalar)
reachability problem, by requiring that the matrix product, acting by right
multiplication on a prescribed row vector, gives another prescribed row vector
(resp. when multiplied at left and right by prescribed row and column vectors,
gives a prescribed scalar). We show that over any semiring, scalar reachability
reduces to vector reachability which is equivalent to matrix reachability, and
that for any of these problems, the specialization to any is
equivalent to the specialization to . As an application of this result and
of a theorem of Krob, we show that when , the vector and matrix
reachability problems are undecidable over the max-plus semiring
. We also show that the matrix, vector, and scalar
reachability problems are decidable over semirings whose elements are
``positive'', like the tropical semiring .Comment: 21 page
First-Principles Calculations of Spinodal Ordering Temperature and Diffuse Intensity Scattering Spectrum for Fe-Pt System
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Containment and equivalence of weighted automata: Probabilistic and max-plus cases
This paper surveys some results regarding decision problems for probabilistic and max-plus automata, such as containment and equivalence. Probabilistic and max-plus automata are part of the general family of weighted automata, whose semantics are maps from words to real values. Given two weighted automata, the equivalence problem asks whether their semantics are the same, and the containment problem whether one is point-wise smaller than the other one. These problems have been studied intensively and this paper will review some techniques used to show (un)decidability and state a list of open questions that still remain
Quiver Theories from D6-branes via Mirror Symmetry
We study N=1 four dimensional quiver theories arising on the worldvolume of
D3-branes at del Pezzo singularities of Calabi-Yau threefolds. We argue that
under local mirror symmetry D3-branes become D6-branes wrapped on a three torus
in the mirror manifold. The type IIB (p,q) 5-brane web description of the local
del Pezzo, being closely related to the geometry of its mirror manifold,
encodes the geometry of 3-cycles and is used to obtain gauge groups, quiver
diagrams and the charges of the fractional branes.Comment: 30 pages, citations adde
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