728,718 research outputs found
Analysis of approximate nearest neighbor searching with clustered point sets
We present an empirical analysis of data structures for approximate nearest
neighbor searching. We compare the well-known optimized kd-tree splitting
method against two alternative splitting methods. The first, called the
sliding-midpoint method, which attempts to balance the goals of producing
subdivision cells of bounded aspect ratio, while not producing any empty cells.
The second, called the minimum-ambiguity method is a query-based approach. In
addition to the data points, it is also given a training set of query points
for preprocessing. It employs a simple greedy algorithm to select the splitting
plane that minimizes the average amount of ambiguity in the choice of the
nearest neighbor for the training points. We provide an empirical analysis
comparing these two methods against the optimized kd-tree construction for a
number of synthetically generated data and query sets. We demonstrate that for
clustered data and query sets, these algorithms can provide significant
improvements over the standard kd-tree construction for approximate nearest
neighbor searching.Comment: 20 pages, 8 figures. Presented at ALENEX '99, Baltimore, MD, Jan
15-16, 199
PRICE-RESPONSE ASYMMETRY IN DOMESTIC WHOLESALE AND RETAIL DIESEL 2 MARKETS IN PERU
This paper tests and confirms the hypothesis that retail and wholesale Diesel 2 prices respond more quickly to increases than to decreases in wholesale and crude oil prices, respectively. Among the possible sources of this asymmetry, we find: production / inventory adjustment lags, refining adjustments, market power of some sellers, searching costs, among others. By analyzing price transmission at different points of the distribution chain, this paper attempts to shed light on these theories for the Peruvian oil industry. Wholesale prices for Diesel 2 show asymmetry in responding to crude oil price changes, which may refl ect inventory adjustment effects. Asymmetry also appears in the response that retail prices give to wholesale price changes, presumably indicating short-run local market power among retailers or the existence of searching costs.Price-response asymmetry, oil, Diesel 2 prices, impulse response analysis
Use of the MultiNest algorithm for gravitational wave data analysis
We describe an application of the MultiNest algorithm to gravitational wave
data analysis. MultiNest is a multimodal nested sampling algorithm designed to
efficiently evaluate the Bayesian evidence and return posterior probability
densities for likelihood surfaces containing multiple secondary modes. The
algorithm employs a set of live points which are updated by partitioning the
set into multiple overlapping ellipsoids and sampling uniformly from within
them. This set of live points climbs up the likelihood surface through nested
iso-likelihood contours and the evidence and posterior distributions can be
recovered from the point set evolution. The algorithm is model-independent in
the sense that the specific problem being tackled enters only through the
likelihood computation, and does not change how the live point set is updated.
In this paper, we consider the use of the algorithm for gravitational wave data
analysis by searching a simulated LISA data set containing two non-spinning
supermassive black hole binary signals. The algorithm is able to rapidly
identify all the modes of the solution and recover the true parameters of the
sources to high precision.Comment: 18 pages, 4 figures, submitted to Class. Quantum Grav; v2 includes
various changes in light of referee's comment
Algorithms for morphological profile filters and their comparison
Morphological filters, regarded as the complement of mean-line based filters, are useful in the analysis of surface texture and the prediction of functional performance. The paper first recalls two existing algorithms, the naive algorithm and the motif combination algorithm, originally developed for the traditional envelope filter. With minor extension, they could be used to compute morphological filters. A recent novel approach based on the relationship between the alpha shape and morphological closing and opening operations is presented as well. Afterwards two novel algorithms are developed. By correlating the convex hull and morphological operations, the Graham scan algorithm, original developed for the convex hull is modified to compute the morphological envelopes. The alpha shape method depending on the Delaunay triangulation is costly and redundant for the computation for the alpha shape for a given radius. A recursive algorithm is proposed to solve this problem. A series of observations are presented for searching the contact points. Based on the proposed observations, the algorithm partitions the profile data into small segments and searches the contact points in a recursive manner. The paper proceeds to compare the five distinct algorithms in five aspects: algorithm verification, algorithm analysis, performance evaluation, end effects correction, and areal extension. By looking into these aspects, the merits and shortcomings of these algorithms are evaluated and compared
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