669 research outputs found
Characteristic extraction tool for gravitational waveforms
We develop and calibrate a characteristic waveform extraction tool whose major improvements and corrections of prior versions allow satisfaction of the accuracy standards required for advanced LIGO data analysis. The extraction tool uses a characteristic evolution code to propagate numerical data on an inner worldtube supplied by a 3+1 Cauchy evolution to obtain the gravitational waveform at null infinity. With the new extraction tool, high accuracy and convergence of the numerical error can be demonstrated for an inspiral and merger of mass M binary black holes even for an extraction worldtube radius as small as R=20M. The tool provides a means for unambiguous comparison between waveforms generated by evolution codes based upon different formulations of the Einstein equations and based upon different numerical approximations
Comparison of Various Improved-Partition Fuzzy c-Means Clustering Algorithms in Fast Color Reduction
This paper provides a comparative study of sev-
eral enhanced versions of the fuzzy
c
-means clustering al-
gorithm in an application of histogram-based image color
reduction. A common preprocessing is performed before clus-
tering, consisting of a preliminary color quantization, histogram
extraction and selection of frequently occurring colors of the
image. These selected colors will be clustered by tested
c
-means
algorithms. Clustering is followed by another common step,
which creates the output image. Besides conventional hard
(HCM) and fuzzy
c
-means (FCM) clustering, the so-called
generalized improved partition FCM algorithm, and several
versions of the suppressed FCM (s-FCM) in its conventional
and generalized form, are included in this study. Accuracy is
measured as the average color difference between pixels of the
input and output image, while efficiency is mostly characterized
by the total runtime of the performed color reduction. Nu-
merical evaluation found all enhanced FCM algorithms more
accurate, and four out of seven enhanced algorithms faster than
FCM. All tested algorithms can create reduced color images of
acceptable quality
Strategies for the characteristic extraction of gravitational waveforms
We develop, test, and compare new numerical and geometrical methods for improving the accuracy of extracting waveforms using characteristic evolution. The new numerical method involves use of circular boundaries to the stereographic grid patches which cover the spherical cross sections of the outgoing null cones. We show how an angular version of numerical dissipation can be introduced into the characteristic code to damp the high frequency error arising form the irregular way the circular patch boundary cuts through the grid. The new geometric method involves use of the Weyl tensor component Psi4 to extract the waveform as opposed to the original approach via the Bondi news function. We develop the necessary analytic and computational formula to compute the O(1/r) radiative part of Psi4 in terms of a conformally compactified treatment of null infinity. These methods are compared and calibrated in test problems based upon linearized waves
Optimal simple monetary policy rules and welfare in a DSGE Model for Hungary
We explore the properties of welfare-maximizing monetary policy in a medium-scale DSGE model for Hungary. In order to make our results operational from a policymaker’s perspective, we approximate the optimal policy rule with a set of simple rules reacting only to observable variables. Our results suggest that “science of monetary policy” that is found robust in simple models, holds in this medium-scaled setting as well. That is, the welfare-maximizing policy that aims to eliminate distortions associated with nominal rigidities can be approximated by a simple inflation targeting rule. Adding exchange rate into the feedback rule only marginally improves the stabilization properties of the policy rule. However, a rule reacting to wage inflation can be significantly welfare-improving. These results may suggest that in our medium-sized model the distortions associated with sticky wage setting have at least as important welfare implications as those related to the price stickiness in product markets.monetary policy, central banking, policy design
Unambiguous determination of gravitational waveforms from binary black hole mergers
Gravitational radiation is properly defined only at future null infinity
(\scri), but in practice it is estimated from data calculated at a finite
radius. We have used characteristic extraction to calculate gravitational
radiation at \scri for the inspiral and merger of two equal mass non-spinning
black holes. Thus we have determined the first unambiguous merger waveforms for
this problem. The implementation is general purpose, and can be applied to
calculate the gravitational radiation, at \scri, given data at a finite
radius calculated in another computation.Comment: 4 pages, 3 figures, published versio
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