16,037,379 research outputs found
Finally, results from Gravity Probe-B
Nearly fifty years after its inception, the Gravity Probe B satellite mission
delivers the first measurements of how a spinning gyroscope precesses in the
gravitational warping of spacetime.Comment: A Viewpoint article, published in Physics 4, 43 (2011), available at
http://physics.aps.org/articles/v4/43 Submitted to the arXiv by permission of
the American Physical Societ
Dynamic temperature selection for parallel-tempering in Markov chain Monte Carlo simulations
Modern problems in astronomical Bayesian inference require efficient methods
for sampling from complex, high-dimensional, often multi-modal probability
distributions. Most popular methods, such as Markov chain Monte Carlo sampling,
perform poorly on strongly multi-modal probability distributions, rarely
jumping between modes or settling on just one mode without finding others.
Parallel tempering addresses this problem by sampling simultaneously with
separate Markov chains from tempered versions of the target distribution with
reduced contrast levels. Gaps between modes can be traversed at higher
temperatures, while individual modes can be efficiently explored at lower
temperatures. In this paper, we investigate how one might choose the ladder of
temperatures to achieve more efficient sampling, as measured by the
autocorrelation time of the sampler. In particular, we present a simple,
easily-implemented algorithm for dynamically adapting the temperature
configuration of a sampler while sampling. This algorithm dynamically adjusts
the temperature spacing to achieve a uniform rate of exchanges between chains
at neighbouring temperatures. We compare the algorithm to conventional
geometric temperature configurations on a number of test distributions and on
an astrophysical inference problem, reporting efficiency gains by a factor of
1.2-2.5 over a well-chosen geometric temperature configuration and by a factor
of 1.5-5 over a poorly chosen configuration. On all of these problems a sampler
using the dynamical adaptations to achieve uniform acceptance ratios between
neighbouring chains outperforms one that does not.Comment: 21 pages, 21 figure
If the government wants to introduce a real revolution in law and order, it should devolve powers and budgets for all criminal justice and emergency services to PCCs
Will Tanner argues that if the Prime Minister is serious about his ‘tough but intelligent’ approach to crime and justice then resources should be directed to what is proven to work. The astonishing success of the Violence Reduction Unit (VRU) in Glasgow is just such a project. Only through such localism could initiatives like the VRU become the norm
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Police force mergers are unnecessary and miss the point; the best policing is local
Much of the focus during the PCC elections has been on the principle of representation. Will Tanner argues that localism is equally important and that the future of policing in England and Wales must be local and democratic, not regional and bureaucratic
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