The Complexity of Primal-Dual Fixed Point Methods for Ridge Regression

We study the ridge regression (L2 regularized least squares) problem and its dual, which is also a ridge regression problem. We observe that the optimality conditions describing the primal and dual optimal solutions can be formulated in several different but equivalent ways. The optimality conditions we identify form a linear system involving a structured matrix depending on a single relaxation parameter which we introduce for regularization purposes. This leads to the idea of studying and comparing, in theory and practice, the performance of the fixed point method applied to these reformulations. We compute the optimal relaxation parameters and uncover interesting connections between the complexity bounds of the variants of the fixed point scheme we consider. These connections follow from a close link between the spectral properties of the associated matrices. For instance, some reformulations involve purely imaginary eigenvalues; some involve real eigenvalues and others have all eigenvalues on the complex circle. We show that the deterministic Quartz method---which is a special case of the randomized dual coordinate ascent method with arbitrary sampling recently developed by Qu, Richt\'{a}rik and Zhang---can be cast in our framework, and achieves the best rate in theory and in numerical experiments among the fixed point methods we study. Remarkably, the method achieves an accelerated convergence rate. Numerical experiments indicate that our main algorithm is competitive with the conjugate gradient method.Comment: 29 pages, 5 algorithms, 8 figures, 2 tables (this is a revision

FADI: a fault-tolerant environment for open distributed computing

FADI is a complete programming environment that serves the reliable execution of distributed application programs. FADI encompasses all aspects of modern fault-tolerant distributed computing. The built-in user-transparent error detection mechanism covers processor node crashes and hardware transient failures. The mechanism also integrates user-assisted error checks into the system failure model. The nucleus non-blocking checkpointing mechanism combined with a novel selective message logging technique delivers an efficient, low-overhead backup and recovery mechanism for distributed processes. FADI also provides means for remote automatic process allocation on the distributed system nodes

Oxidation and reduction rates for organic carbon in the Amazon mainstream tributary and floodplain, inferred from distributions of dissolved gases

Concentrations of CO2, O2, CH4, and N2O in the Amazon River system reflect an oxidation-reduction sequence in combination with physical mixing between the floodplain and the mainstem. Concentrations of CO2 ranged from 150 microM in the Amazon mainstem to 200 to 300 microM in aerobic waters of the floodplain, and up to 1000 microM in oxygen-depleted environments. Apparent oxygen utilization (AOU) ranged from 80 to 250 microM. Methane was highly supersaturated, with concentrations ranging from 0.06 microM in the mainstem to 100 microM on the floodplain. Concentrations of N2O were slightly supersaturated in the mainstem, but were undersaturated on the floodplain. Fluxes calculated from these concentrations indicated decomposition of 1600 g C sq m y(-1) of organic carbon in Amazon floodplain waters. Analysis of relationships between CH4, O2, and CO2 concentrations indicated that approximately 50 percent of carbon mineralization on the floodplain is anaerobic, with 20 percent lost to the atmoshphere as CH4. The predominance of anaerobic metabolism leads to consumption of N2O on the flood plane. Elevated concentrations of CH4 in the mainstem probably reflect imput from the floodplain, while high levels of CO2 in the mainstem are derived from a combination of varzea drainage and in situ respiration

Stacking tolerance to drought and resistance to a parasitic weed in tropical hybrid maize for enhancing resilience to stress combinations

Open Access JournalMaize is a food security crop cultivated in the African savannas that are vulnerable to the occurrence of drought stress and Striga hermonthica infestation. The co-occurrence of these stresses can severely damage crop growth and productivity of maize. Until recently, maize breeding in International Institute of Tropical Agriculture (IITA) has focused on the development of either drought tolerant or S. hermonthica resistant germplasm using independent screening protocols. The present study was therefore conducted to examine the extent to which maize hybrids simultaneously expressing resistance to S. hermonthica and tolerance to drought (DTSTR) could be developed through sequential selection of parental lines using the two screening protocols. Regional trials involving 77 DTSTR and 22 commercial benchmark hybrids (STR and non-DTSTR) were then conducted under Striga-infested and non-infested conditions, managed drought stress and fully irrigated conditions as well as in multiple rainfed environments for 5 years. The observed yield reductions of 61% under managed drought stress and 23% under Striga-infestation created desirable stress levels leading to the detection of significant differences in grain yield among hybrids at individual stress and non-stress conditions. On average, the DTSTR hybrids out-yielded the STR and non-DTSTR commercial hybrids by 13–19% under managed drought stress and fully irrigated conditions and by −4 to 70% under Striga-infested and non-infested conditions. Among the DTSTR hybrids included in the regional trials, 33 were high yielders with better adaptability across environments under all stressful and non-stressful testing conditions. Twenty-four of the 33 DTSTR hybrids also yielded well across diverse rainfed environments. The genetic correlations of grain yield under managed drought stress with yield under Striga-infestation and multiple rainfed environments were 0.51 and 0.57, respectively. Also, a genetic correlation between yields under Striga-infestation with that recorded in multiple rainfed environments was 0.58. These results suggest that the sequential selection scheme offers an opportunity to accumulate desirable stress-related traits in parents contributing to superior agronomic performance in hybrids across stressful and diverse rainfed field environments that are commonly encountered in the tropical savannas of Africa

Career guidance for social justice: Webinar, March 11, 2022

This article is a summary of the main issues and discussions raised at a webinar organised by the Career Guidance for Social Justice website on the 11th March 2022

A SYSTEMATIC REVIEW FOR CREATIVE THINKING SKILLS IN PHYSICS SUBJECTS

This study aims to obtain information on efforts to improve high school students creative thinking abilities in physics learning. The review method was chosen to obtain research journals with keywords in students' creative thinking abilities in high school physics learning with Google undergraduate reference sources, hands-on science, and research gates. Twenty-five journals were reviewed based on author (year), research design, creative thinking skills, and findings. Based on a study of 15 international and ten national articles, applying the Problem Based Solving learning model is the most widely used effort to improve creative thinking skills. In addition to Problem-Based Learning, several efforts can be made to enhance creative thinking skills, including implementing Project Based Learning, Creative Problem Solving, and developing physics learning tools. This research can contribute to the world of education, especially in evaluating physics learning

Does it have to be so complicated? : municipal renewable energy projects in Massachusetts

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2006.Includes bibliographical references (leaves 95-97).This thesis examines municipal implementation of renewable energy projects in Massachusetts. It explores projects that have been planned and completed, drivers for municipal adoption of renewable energy, the implementation experience, barriers, and key success factors. The data presented include a survey of Massachusetts municipalities, stakeholder interviews, and an in-depth case study of a solar Brightfield project implemented in Brockton, Massachusetts. The case study describes in detail the city's experience implementing a "Brownfields to Brightfields" solar project initiated through the US Department of Energy's Brightfields program. The Brockton Brightfield is a 425 kW utility scale solar array on a former brownfield site. The case study of Brockton's Brightfields experience reveals a series of obstacles and success factors that ought to be considered in future efforts to implement municipal renewable energy projects. The barriers include inadequate government resources and capacity building dedicated to program implementation; institutional policy barriers (requiring legislative fixes), and the complexity surrounding the joint action required to navigate the administrative processes involved. The thesis concludes with a series of policy recommendations.(cont.) Recommended state legislative changes include 1) providing municipalities explicit legal authority to finance, develop, operate and maintain alternative energy projects; 2) increasing the allowable length of time for municipal borrowing for alternative energy from ten to twenty years; 3) clarifying procurement regulations; 4) increasing the net metering limit; 5) modifying interconnection standards to allow electricity generated at one municipal site to be used at another; and, 6) allowing third party behind the meter power sales. The thesis further recommends both federal and state adoption of sufficient and consistent grant and financing programs required to assist local governments. Finally, the thesis identifies a provision in the Massachusetts constitution regarding protection of open space and conservation land that municipalities must be aware of in identifying municipal land available for renewable energy projects. Special legislation may be required for individual projects.by Lori A. Riberio.S.M

Towards a virtual museum of public art and urban design

[eng] This article comes from the communication that the authors presented at the International Seminar on "Public Art and Urban Design" held in Almada (Portugal) in 2006 and later in Barcelona, 2007. Through a series of questions, the authors raise the issues of production, management and dissemination of public art in the context of Urban Design. These questions arise from the analysis carried out on a series of manuals of "good practice" disseminated by several municipalities and public agencies devoted to the Public Art Finally, the authors outline the open possibilities for a Virtual Museum of Public Art and Urban Design, based on the existence of Public Art Information Systems that have cities like Barcelona and Saragossa and that are being developed in Lisbon and Almada.[por] Este artigo trata da comunicação de que os autores apresentaram no Seminário Internacional sobre "Arte Pública e Desenho Urbano", realizado em Almada (Portugal) em 2006 e depois em Barcelona, 2007. Através de uma série de perguntas, os autores levantam as questões de Produção, Gestão e Difusão da arte pública no contexto do Desenho Urbano. Estas questões surgem a partir da análise realizada sobre uma série de manuais de boas práticas divulgados por vários municípios e órgãos públicos dedicados à Arte Pública. Finalmente, os autores descrevem as possibilidades para um Museu Virtual da Arte Pública e o Desenho Urbano, com base na existência de Sistemas de Informação da Arte Pública que existem em cidades como Barcelona e Saragoça e que estão sendo desenvolvidos em Lisboa e Almad