3,421 research outputs found
Estimates for the volume of a Lorentzian manifold
We prove new estimates for the volume of a Lorentzian manifold and show
especially that cosmological spacetimes with crushing singularities have finite
volume.Comment: 8 pages, a pdf version of the preprint can also be retrieved from
http://www.math.uni-heidelberg.de/studinfo/gerhardt/LM-Volume.pdf v2: A
further estimate has been added covering the case when the mean curvature is
merely non-negative resp. non-positive (Theorem 1.1
South Dakota Mosquitoes and Their Control
This bulletin is intended for extension service personnel, local health agencies, and city or county personnel who may have occasion to use the information. It is not an entomological treatise and thus omits species synonymy and the usual collection data of more precise distributional studies. The use of coined or registered trade names of insecticides or equipment does not constitute an endorsement of these products by South Dakota State University or the author and criticism is not implied of products not mentioned
Accelerating Large-Scale Data Analysis by Offloading to High-Performance Computing Libraries using Alchemist
Apache Spark is a popular system aimed at the analysis of large data sets,
but recent studies have shown that certain computations---in particular, many
linear algebra computations that are the basis for solving common machine
learning problems---are significantly slower in Spark than when done using
libraries written in a high-performance computing framework such as the
Message-Passing Interface (MPI).
To remedy this, we introduce Alchemist, a system designed to call MPI-based
libraries from Apache Spark. Using Alchemist with Spark helps accelerate linear
algebra, machine learning, and related computations, while still retaining the
benefits of working within the Spark environment. We discuss the motivation
behind the development of Alchemist, and we provide a brief overview of its
design and implementation.
We also compare the performances of pure Spark implementations with those of
Spark implementations that leverage MPI-based codes via Alchemist. To do so, we
use data science case studies: a large-scale application of the conjugate
gradient method to solve very large linear systems arising in a speech
classification problem, where we see an improvement of an order of magnitude;
and the truncated singular value decomposition (SVD) of a 400GB
three-dimensional ocean temperature data set, where we see a speedup of up to
7.9x. We also illustrate that the truncated SVD computation is easily scalable
to terabyte-sized data by applying it to data sets of sizes up to 17.6TB.Comment: Accepted for publication in Proceedings of the 24th ACM SIGKDD
International Conference on Knowledge Discovery and Data Mining, London, UK,
201
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