A Regularized Jacobi Method for Large-Scale Linear Programming

A parallel algorithm based on Jacobi iterations is proposed to minimize the augmented Lagrangian functions of the multiplier method for large-scale linear programming. Sparsity is efficiently exploited for determining stepsizes (column-wise) for the Jacobi iterations. Linear convergence is shown with convergence ratio depending on sparsity but not on the penalty parameter and on problem size. Employing simulation of parallel computations, an experimental code is tested extensively on 68 Netlib problems. Results are compared with the simplex method, an interior point algorithm and a Gauss-Seidel approach. We observe that speedup against the simplex method generally increases with the problem size, while the parallel solution times increase slowly, if at all. Our preliminary results compared with the other two methods are highly encouraging as well

Stochastic Resonance: influence of a f−κf^{-\kappa} noise spectrum

Here, in order to study \textit{stochastic resonance} (SR) in a double-well potential when the noise source has a spectral density of the form $f^{-\kappa}$ with varying $\kappa$, we have extended a procedure, introduced by Kaulakys et al (Phys. Rev. E \textbf{70}, 020101 (2004)). In order to have an analytical understanding of the results, we have obtained an effective Markovian approximation, that allows us to make a systematic study of the effect of such kind of noises on the SR phenomenon. The comparison of numerical and analytical results shows an excellent qualitative agreement indicating that the effective Markovian approximation is able to correctly describe the general trends.Comment: 11 pages, 6 figures, submitted to Euro.Phys.J.

Robust Algorithm to Generate a Diverse Class of Dense Disordered and Ordered Sphere Packings via Linear Programming

We have formulated the problem of generating periodic dense paritcle packings as an optimization problem called the Adaptive Shrinking Cell (ASC) formulation [S. Torquato and Y. Jiao, Phys. Rev. E {\bf 80}, 041104 (2009)]. Because the objective function and impenetrability constraints can be exactly linearized for sphere packings with a size distribution in $d$-dimensional Euclidean space $\mathbb{R}^d$, it is most suitable and natural to solve the corresponding ASC optimization problem using sequential linear programming (SLP) techniques. We implement an SLP solution to produce robustly a wide spectrum of jammed sphere packings in $\mathbb{R}^d$ for $d=2,3,4,5$ and $6$ with a diversity of disorder and densities up to the maximally densities. This deterministic algorithm can produce a broad range of inherent structures besides the usual disordered ones with very small computational cost by tuning the radius of the {\it influence sphere}. In three dimensions, we show that it can produce with high probability a variety of strictly jammed packings with a packing density anywhere in the wide range $[0.6, 0.7408...]$. We also apply the algorithm to generate various disordered packings as well as the maximally dense packings for $d=2,3, 4,5$ and 6. Compared to the LS procedure, our SLP protocol is able to ensure that the final packings are truly jammed, produces disordered jammed packings with anomalously low densities, and is appreciably more robust and computationally faster at generating maximally dense packings, especially as the space dimension increases.Comment: 34 pages, 6 figure

Exposition de la population française aux champs magnétiques 50 Hz : résultats partiels

Les champs magnétiques (CM) alternatifs de fréquence 50 Hz, liés à l'électricité en particulier, sont suspectés depuis une trentaine d'années d'être responsables de pathologies, notamment de leucémies chez l'enfant [1]. Les dernières expertises collectives (OMS 2007, SCENHIR 2009) ont conclu que la dernière grande interrogation en ce qui concerne les CM basse fréquence est l'association statistique observée dans plusieurs analyses conjointes entre l'augmentation du risque de leucémie de l'enfant et une exposition aux CM supérieure à 0,4 μT en valeur moyenne sur 24 h [2]. Actuellement, l'exposition de la population française à ces champs n'est connue que de manière très approximative. Une étude effectuée dans le département de la Côte d'Or sur des logements situés à proximité de lignes à haute et très haute tension a permis d'évaluer les expositions à l'intérieur de ces logements [3]. Mais, d'une part il s'agit d'un faible échantillon compte tenu de la diversité du parc de logements en France, d'autre part, il s'agit d'une exposition du logement et non des personnes. En effet, tout un chacun est exposé à de nombreuses sources de champ magnétique du simple fait qu'on ne reste pas chez soi 24 heures sur 24. Les transports, en particulier, représentent des sources d'exposition significatives, mais d'autres lieux de vie peuvent constituer des sources d'exposition, que ce soit le lieu de travail, le terrain de sport, le centre commercial ou l'école. Dans le cas où le CM supérieur 0,4 μT en moyenne représenterait un risque pour la santé, comment estimer la proportion de la population française à risque et identifier les sources favorisant l'exposition ? Pour répondre à cette question, la Direction Générale de la Santé a initié une étude sur l'exposition aux CM 50 Hz d'un échantillon représentatif de la population française. Une des problématiques de cette étude a été de réaliser cet échantillon et de collecter toutes les informations nécessaires. Pour réaliser cette étude, le recrutement des volontaires et les mesures du CM ont été effectués en trois campagnes. Nous présentons les résultats des deux premières campagnes

French population exposure to 50 Hz magnetic fields : intermediate results

International audienceFor the last thirty years, the electricity related 50 Hz magnetic fields (MF) have been suspected of being responsible for several pathologies, in particular childhood leukemia [1]. The most recent collective expertise (WHO 2007 and SCENHIR 2009) concluded that the last major interrogation with regard to low frequency MF is the statistical association observed in several joint analyses between the increase of risk of the childhood leukemia and a higher than 0.4 μT exposure to MF on average in a 24-hour period [2]. Currently, the exposure of the French population to these magnetic fields is only approximately known. A study carried out in residences located near high voltage power lines in the "département1 de la Côte d'Or" made it possible to assess the MF background level inside these residences [3]. However, these residences are a limited sample compared to the diversity of the housing developments in France and the study characterized the exposure of the houses and not of the resident people. We are all exposed to many sources of magnetic fields due the fact that we do not remain at home 24 hours a day. Transportation in particular, significantly contributes to the individual exposure. Other places or activities can also constitute sources of exposure such as the workplace, sport activity areas, shopping centers or schools. Should the MF in excess to 0.4 μT on average carry health risk, would the authorities be able to manage it, i.e. estimate the proportion of the French population at risk and identify and mitigate the main sources causing the exposure? To answer this question the Ministry of Health and Solidarities initiated a study on the exposure of a representative sample of the French population to 50 Hz MF. The major issues of this study were to select randomly a representative sample and to collect all of necessary data. Measurements were performed in three campaigns at winter time (October to April). The present paper gives the results of the two first campaigns

MM Algorithms for Geometric and Signomial Programming

This paper derives new algorithms for signomial programming, a generalization of geometric programming. The algorithms are based on a generic principle for optimization called the MM algorithm. In this setting, one can apply the geometric-arithmetic mean inequality and a supporting hyperplane inequality to create a surrogate function with parameters separated. Thus, unconstrained signomial programming reduces to a sequence of one-dimensional minimization problems. Simple examples demonstrate that the MM algorithm derived can converge to a boundary point or to one point of a continuum of minimum points. Conditions under which the minimum point is unique or occurs in the interior of parameter space are proved for geometric programming. Convergence to an interior point occurs at a linear rate. Finally, the MM framework easily accommodates equality and inequality constraints of signomial type. For the most important special case, constrained quadratic programming, the MM algorithm involves very simple updates.Comment: 16 pages, 1 figur

The impact on staff of working with personality disordered offenders: A systematic review

© 2015 Freestone et al. Background: Personality disordered offenders (PDOs) are generally considered difficult to manage and to have a negative impact on staff working with them. Aims: This study aimed to provide an overview of studies examining the impact on staff of working with PDOs, identify impact areas associated with working with PDOs, identify gaps in existing research,and direct future research efforts. Methods: The authors conducted a systematic review of the English-language literature from 1964-2014 across 20 databases in the medical and social sciences. Results: 27 papers were included in the review. Studies identified negative impacts upon staff including: negative attitudes, burnout, stress, negative counter-transferential experiences; two studies found positive impacts of job excitement and satisfaction, and the evidence related to perceived risk of violence from PDOs was equivocal. Studies demonstrated considerable heterogeneity and meta-analysis was not possible. The overall level of identified evidence was low: 23 studies (85%) were descriptive only, and only one adequately powered cohort study was found. Conclusions: The review identified a significant amount of descriptive literature, but only one cohort study and no trials or previous systematic reviews of literatures. Clinicians and managers working with PDOs should be aware of the potential impacts identified, but there is an urgent need for further research focusing on the robust evaluation of interventions to minimise harm to staff working with offenders who suffer from personality disorder Copyright

The Continuous Sample of Working Lives: improving its representativeness

This paper studies the representativeness of the Continuous Sample of Working Lives (CSWL), a set of anonymized microdata containing information on individuals from Spanish Social Security records. We examine several CSWL waves (2005-2013) and show that it is not representative for the population with a pension income. We then develop a methodology to draw a large dataset from the CSWL that is much more representative of the retired population in terms of pension type, gender and age. This procedure also makes it possible for users to choose between goodness of fit and subsample size. In order to illustrate the practical significance of our methodology, the paper also contains an application in which we generate a large subsample distribution from the 2010 CSWL. The results are striking: with a very small reduction in the size of the original CSWL, we significantly reduce errors in estimating pension expenditure for 2010, with a p value greater or equal to 0.999