2,101 research outputs found
Generic Subsequence Matching Framework: Modularity, Flexibility, Efficiency
Subsequence matching has appeared to be an ideal approach for solving many
problems related to the fields of data mining and similarity retrieval. It has
been shown that almost any data class (audio, image, biometrics, signals) is or
can be represented by some kind of time series or string of symbols, which can
be seen as an input for various subsequence matching approaches. The variety of
data types, specific tasks and their partial or full solutions is so wide that
the choice, implementation and parametrization of a suitable solution for a
given task might be complicated and time-consuming; a possibly fruitful
combination of fragments from different research areas may not be obvious nor
easy to realize. The leading authors of this field also mention the
implementation bias that makes difficult a proper comparison of competing
approaches. Therefore we present a new generic Subsequence Matching Framework
(SMF) that tries to overcome the aforementioned problems by a uniform frame
that simplifies and speeds up the design, development and evaluation of
subsequence matching related systems. We identify several relatively separate
subtasks solved differently over the literature and SMF enables to combine them
in straightforward manner achieving new quality and efficiency. This framework
can be used in many application domains and its components can be reused
effectively. Its strictly modular architecture and openness enables also
involvement of efficient solutions from different fields, for instance
efficient metric-based indexes. This is an extended version of a paper
published on DEXA 2012.Comment: This is an extended version of a paper published on DEXA 201
Non-Gaussian Component Analysis using Entropy Methods
Non-Gaussian component analysis (NGCA) is a problem in multidimensional data
analysis which, since its formulation in 2006, has attracted considerable
attention in statistics and machine learning. In this problem, we have a random
variable in -dimensional Euclidean space. There is an unknown subspace
of the -dimensional Euclidean space such that the orthogonal
projection of onto is standard multidimensional Gaussian and the
orthogonal projection of onto , the orthogonal complement
of , is non-Gaussian, in the sense that all its one-dimensional
marginals are different from the Gaussian in a certain metric defined in terms
of moments. The NGCA problem is to approximate the non-Gaussian subspace
given samples of .
Vectors in correspond to `interesting' directions, whereas
vectors in correspond to the directions where data is very noisy. The
most interesting applications of the NGCA model is for the case when the
magnitude of the noise is comparable to that of the true signal, a setting in
which traditional noise reduction techniques such as PCA don't apply directly.
NGCA is also related to dimension reduction and to other data analysis problems
such as ICA. NGCA-like problems have been studied in statistics for a long time
using techniques such as projection pursuit.
We give an algorithm that takes polynomial time in the dimension and has
an inverse polynomial dependence on the error parameter measuring the angle
distance between the non-Gaussian subspace and the subspace output by the
algorithm. Our algorithm is based on relative entropy as the contrast function
and fits under the projection pursuit framework. The techniques we develop for
analyzing our algorithm maybe of use for other related problems
Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interaction
Chiral magnets are an emerging class of topological matter harbouring
localized and topologically protected vortex-like magnetic textures called
skyrmions, which are currently under intense scrutiny as a new entity for
information storage and processing. Here, on the level of micromagnetics we
rigorously show that chiral magnets cannot only host skyrmions but also
antiskyrmions as least-energy configurations over all non-trivial homotopy
classes. We derive practical criteria for their occurrence and coexistence with
skyrmions that can be fulfilled by (110)-oriented interfaces in dependence on
the electronic structure. Relating the electronic structure to an atomistic
spin-lattice model by means of density-functional calculations and minimizing
the energy on a mesoscopic scale applying spin-relaxation methods, we propose a
double layer of Fe grown on a W(110) substrate as a practical example. We
conjecture that ultrathin magnetic films grown on semiconductor or heavy metal
substrates with symmetry are prototype classes of materials hosting
magnetic antiskyrmions.Comment: 20 pages (11 pages + 9 pages supplementary material
A Lower Bound Technique for Communication in BSP
Communication is a major factor determining the performance of algorithms on
current computing systems; it is therefore valuable to provide tight lower
bounds on the communication complexity of computations. This paper presents a
lower bound technique for the communication complexity in the bulk-synchronous
parallel (BSP) model of a given class of DAG computations. The derived bound is
expressed in terms of the switching potential of a DAG, that is, the number of
permutations that the DAG can realize when viewed as a switching network. The
proposed technique yields tight lower bounds for the fast Fourier transform
(FFT), and for any sorting and permutation network. A stronger bound is also
derived for the periodic balanced sorting network, by applying this technique
to suitable subnetworks. Finally, we demonstrate that the switching potential
captures communication requirements even in computational models different from
BSP, such as the I/O model and the LPRAM
SciQL, Bridging the Gap between Science and Relational DBMS
Scientific discoveries increasingly rely on the ability to efficiently grind massive amounts of experimental data using database technologies. To bridge the gap between the needs of the Data-Intensive Research fields and the current DBMS technologies, we propose SciQL (pronounced as ‘cycle’), the first SQL-based query language for scientific applications with both tables and arrays as first class citizens. It provides a seamless symbiosis of array-, set- and sequence- interpretations. A key innovation is the extension of value-based grouping of SQL:2003 with structural grouping, i.e., fixed-sized and unbounded groups based on explicit relationships between elements positions. This leads to a generalisation of window-based query processing with wide applicability in science domains. This paper describes the main language features of SciQL and illustrates
it using time-series concepts
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