621 research outputs found
Two New Proofs of Afriat's Theorem
We provide two, new simple proofs of Afriat's celebrated theorem..Afriat's theorem, SARP, GARP
Bayesian estimation for selective trace gas detection
We present a Bayesian estimation analysis for a particular trace gas
detection technique with species separation provided by differential diffusion.
The proposed method collects a sample containing multiple gas species into a
common volume, and then allows it to diffuse across a linear array of optical
absorption detectors, using, for example, high-finesse Fabry-Perot cavities.
The estimation procedure assumes that all gas parameters (e.g. diffusion
constants, optical cross sections) are known except for the number population
of each species, which are determined from the time-of-flight absorption
profiles in each detector
Sums of hermitian squares and the BMV conjecture
Recently Lieb and Seiringer showed that the Bessis-Moussa-Villani conjecture
from quantum physics can be restated in the following purely algebraic way: The
sum of all words in two positive semidefinite matrices where the number of each
of the two letters is fixed is always a matrix with nonnegative trace. We show
that this statement holds if the words are of length at most 13. This has
previously been known only up to length 7. In our proof, we establish a
connection to sums of hermitian squares of polynomials in noncommuting
variables and to semidefinite programming. As a by-product we obtain an example
of a real polynomial in two noncommuting variables having nonnegative trace on
all symmetric matrices of the same size, yet not being a sum of hermitian
squares and commutators.Comment: 21 pages; minor changes; a companion Mathematica notebook is now
available in the source fil
Smart Focal Plane Technologies for VLT Instruments
As we move towards the era of ELTs, it is timely to think about the future
role of the 8-m class telescopes. Under the OPTICON programme, novel
technologies have been developed that are intended for use in multi-object and
integral-field spectrographs. To date, these have been targeted at instrument
concepts for the European ELT, but there are also significant possibilities for
their inclusion in new VLT instruments, ensuring the continued success and
productivity of these unique telescopes.Comment: 5 pages, to appear in the proceedings of the ESO Workshop "Science
with the VLT in the ELT era
Polyhedral Analysis using Parametric Objectives
The abstract domain of polyhedra lies at the heart of many program analysis techniques. However, its operations can be expensive, precluding their application to polyhedra that involve many variables. This paper describes a new approach to computing polyhedral domain operations. The core of this approach is an algorithm to calculate variable elimination (projection) based on parametric linear programming. The algorithm enumerates only non-redundant inequalities of the projection space, hence permits anytime approximation of the output
Strong duality in conic linear programming: facial reduction and extended duals
The facial reduction algorithm of Borwein and Wolkowicz and the extended dual
of Ramana provide a strong dual for the conic linear program in the absence of any constraint qualification. The facial
reduction algorithm solves a sequence of auxiliary optimization problems to
obtain such a dual. Ramana's dual is applicable when (P) is a semidefinite
program (SDP) and is an explicit SDP itself. Ramana, Tuncel, and Wolkowicz
showed that these approaches are closely related; in particular, they proved
the correctness of Ramana's dual using certificates from a facial reduction
algorithm.
Here we give a clear and self-contained exposition of facial reduction, of
extended duals, and generalize Ramana's dual:
-- we state a simple facial reduction algorithm and prove its correctness;
and
-- building on this algorithm we construct a family of extended duals when
is a {\em nice} cone. This class of cones includes the semidefinite cone
and other important cones.Comment: A previous version of this paper appeared as "A simple derivation of
a facial reduction algorithm and extended dual systems", technical report,
Columbia University, 2000, available from
http://www.unc.edu/~pataki/papers/fr.pdf Jonfest, a conference in honor of
Jonathan Borwein's 60th birthday, 201
Structural, item, and test generalizability of the psychopathology checklist - revised to offenders with intellectual disabilities
The Psychopathy Checklist–Revised (PCL-R) is the most widely used measure of psychopathy in forensic clinical practice, but the generalizability of the measure to offenders with intellectual disabilities (ID) has not been clearly established. This study examined the structural equivalence and scalar equivalence of the PCL-R in a sample of 185 male offenders with ID in forensic mental health settings, as compared with a sample of 1,212 male prisoners without ID. Three models of the PCL-R’s factor structure were evaluated with confirmatory factor analysis. The 3-factor hierarchical model of psychopathy was found to be a good fit to the ID PCL-R data, whereas neither the 4-factor model nor the traditional 2-factor model fitted. There were no cross-group differences in the factor structure, providing evidence of structural equivalence. However, item response theory analyses indicated metric differences in the ratings of psychopathy symptoms between the ID group and the comparison prisoner group. This finding has potential implications for the interpretation of PCL-R scores obtained with people with ID in forensic psychiatric settings
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