Parallel structurally-symmetric sparse matrix-vector products on multi-core processors

We consider the problem of developing an efficient multi-threaded implementation of the matrix-vector multiplication algorithm for sparse matrices with structural symmetry. Matrices are stored using the compressed sparse row-column format (CSRC), designed for profiting from the symmetric non-zero pattern observed in global finite element matrices. Unlike classical compressed storage formats, performing the sparse matrix-vector product using the CSRC requires thread-safe access to the destination vector. To avoid race conditions, we have implemented two partitioning strategies. In the first one, each thread allocates an array for storing its contributions, which are later combined in an accumulation step. We analyze how to perform this accumulation in four different ways. The second strategy employs a coloring algorithm for grouping rows that can be concurrently processed by threads. Our results indicate that, although incurring an increase in the working set size, the former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo

Occupational Stress and Instigator Workplace Incivility as Moderated by Personality: A Test of an Occupational Stress and Workplace Incivility Model

This research investigates the relationship between occupational stress and instigator workplace incivility, as moderated by personality, to select organizational outcomes (i.e., perceived physical health and intent to turnover). Data were collected from 206 fulltime working adults in the healthcare industry utilizing Amazon MTurk. Moderated hierarchical regressions were conducted to test the possible moderating role of personality on the stress-incivility relationship; the results demonstrated that conscientiousness and agreeableness dampened the stress-incivility relationship and neuroticism and extraversion strengthened the relationship. Hierarchical regression analyses were conducted also to explore the degree stress and incivility predicted the outcome variables of perceived physical health and intentions to turnover; the data indicated support for the notion that greater stress and incivility positively predicted turnover intent

On the consistency of a repulsive gravity phase in the early Universe

We exploit the possibility of existence of a repulsive gravity phase in the evolution of the Universe. A toy model with a free scalar field minimally coupled to gravity, but with the "wrong sign" for the energy and negative curvature for the spatial section, is studied in detail. The background solutions display a bouncing, non-singular Universe. The model is well-behaved with respect to tensor perturbations. But, it exhibits growing models with respect to scalar perturbations whose maximum occurs in the bouncing. Hence, large inhomogeneties are produced. At least for this case, a repulsive phase may destroy homogeneity, and in this sense it may be unstable. A newtonian analogous model is worked out; it displays qualitatively the same behaviour. The generality of this result is discussed. In particular, it is shown that the addition of an attractive radiative fluid does not change essentially the results. We discuss also a quantum version of the classical repulsive phase, through the Wheeler-de Witt equation in mini-superspace, and we show that it displays essentially the same scenario as the corresponding attractive phase.Comment: Latex file, 15 pages, 7 figures. There is a new figure, a new section and some other minor correction

Teto de gastos: manifestos pró e contra

A Folha de São Paulo publicou recentemente dois interessantes manifestos. O primeiro, assinado por 96 economistas, muitos deles ligados a instituições financeiras privadas, defendeu o teto constitucional de gastos como “âncora fiscal”, apontando medidas para preservá-lo. O segundo, subscrito por 380 economistas e outros profissionais que trabalham com economia, defendeu a extinção do teto, mostrando as implicações de tentar cumpri-lo a todo o custo. O segundo manifesto é uma resposta ao primeiro. Desde então, foram divulgados o Projeto de Lei Orçamentária Anual para 2021 (PLOA-2021), a proposta do governo para a Reforma Administrativa e uma nota do Ministério da Economia sobre teto. Esses três documentos fornecem elementos adicionais, mas não alteram os termos do debate tal como colocados nos dois manifestos de economistas. Chama atenção o número de signatários, sobretudo considerando que os dois textos são longos e entram em detalhes. Uma realização e tanto, não há dúvida, reunir debaixo dos mesmos tetos um grande número de economistas – tribo eminentemente facciosa e propensa à fragmentação. Pois bem, fiel à tradição da tribo a que pertenço, vou botar defeito nos dois manifestos