6,904 research outputs found
Linguistic Optimization
Optimality Theory (OT) is a model of language that combines aspects of generative and connectionist linguistics. It is unique in the field in its use of a rank ordering on constraints, which is used to formalize optimization, the choice of the best of a set of potential linguistic forms. We show that phenomena argued to require ranking fall out equally from the form of optimization in OT's predecessor Harmonic Grammar (HG), which uses numerical weights to encode the relative strength of constraints. We further argue that the known problems for HG can be resolved by adopting assumptions about the nature of constraints that have precedents both in OT and elsewhere in computational and generative linguistics. This leads to a formal proof that if the range of each constraint is a bounded number of violations, HG generates a finite number of languages. This is nontrivial, since the set of possible weights for each constraint is nondenumerably infinite. We also briefly review some advantages of HG
The Ohio State 1991 geopotential and sea surface topography harmonic coefficient models
The computation is described of a geopotential model to deg 360, a sea surface topography model to deg 10/15, and adjusted Geosat orbits for the first year of the exact repeat mission (ERM). This study started from the GEM-T2 potential coefficient model and it's error covariance matrix and Geosat orbits (for 22 ERMs) computed by Haines et al. using the GEM-T2 model. The first step followed the general procedures which use a radial orbit error theory originally developed by English. The Geosat data was processed to find corrections to the a priori geopotential model, corrections to a radial orbit error model for 76 Geosat arcs, and coefficients of a harmonic representation of the sea surface topography. The second stage of the analysis took place by doing a combination of the GEM-T2 coefficients with 30 deg gravity data derived from surface gravity data and anomalies obtained from altimeter data. The analysis has shown how a high degree spherical harmonic model can be determined combining the best aspects of two different analysis techniques. The error analysis was described that has led to the accuracy estimates for all the coefficients to deg 360. Significant work is needed to improve the modeling effort
A Study of a Mini-drift GEM Tracking Detector
A GEM tracking detector with an extended drift region has been studied as
part of an effort to develop new tracking detectors for future experiments at
RHIC and for the Electron Ion Collider that is being planned for BNL or JLAB.
The detector consists of a triple GEM stack with a small drift region that was
operated in a mini TPC type configuration. Both the position and arrival time
of the charge deposited in the drift region were measured on the readout plane
which allowed the reconstruction of a short vector for the track traversing the
chamber. The resulting position and angle information from the vector could
then be used to improve the position resolution of the detector for larger
angle tracks, which deteriorates rapidly with increasing angle for conventional
GEM tracking detectors using only charge centroid information. Two types of
readout planes were studied. One was a COMPASS style readout plane with 400
micron pitch XY strips and the other consisted of 2x10mm2 chevron pads. The
detector was studied in test beams at Fermilab and CERN, along with additional
measurements in the lab, in order to determine its position and angular
resolution for incident track angles up to 45 degrees. Several algorithms were
studied for reconstructing the vector using the position and timing information
in order to optimize the position and angular resolution of the detector for
the different readout planes. Applications for large angle tracking detectors
at RHIC and EIC are also discussed.Comment: Submitted to the IEEE Transactions on Nuclear Scienc
Convergence Analysis of the Approximate Newton Method for Markov Decision Processes
Recently two approximate Newton methods were proposed for the optimisation of
Markov Decision Processes. While these methods were shown to have desirable
properties, such as a guarantee that the preconditioner is
negative-semidefinite when the policy is -concave with respect to the
policy parameters, and were demonstrated to have strong empirical performance
in challenging domains, such as the game of Tetris, no convergence analysis was
provided. The purpose of this paper is to provide such an analysis. We start by
providing a detailed analysis of the Hessian of a Markov Decision Process,
which is formed of a negative-semidefinite component, a positive-semidefinite
component and a remainder term. The first part of our analysis details how the
negative-semidefinite and positive-semidefinite components relate to each
other, and how these two terms contribute to the Hessian. The next part of our
analysis shows that under certain conditions, relating to the richness of the
policy class, the remainder term in the Hessian vanishes in the vicinity of a
local optimum. Finally, we bound the behaviour of this remainder term in terms
of the mixing time of the Markov chain induced by the policy parameters, where
this part of the analysis is applicable over the entire parameter space. Given
this analysis of the Hessian we then provide our local convergence analysis of
the approximate Newton framework.Comment: This work has been removed because a more recent piece (A
Gauss-Newton method for Markov Decision Processes, T. Furmston & G. Lever) of
work has subsumed i
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