Primal-Dual Active-Set Methods for Convex Quadratic Optimization with Applications

Primal-dual active-set (PDAS) methods are developed for solving quadratic optimization problems (QPs). Such problems arise in their own right in optimal control and statistics–two applications of interest considered in this dissertation–and as subproblems when solving nonlinear optimization problems. PDAS methods are promising as they possess the same favorable properties as other active-set methods, such as their ability to be warm-started and to obtain highly accurate solutions by explicitly identifying sets of constraints that are active at an optimal solution. However, unlike traditional active-set methods, PDAS methods have convergence guarantees despite making rapid changes in active-set estimates, making them well suited for solving large-scale problems.Two PDAS variants are proposed for efficiently solving generally-constrained convex QPs. Both variants ensure global convergence of the iterates by enforcing montonicity in a measure of progress. Besides identifying an estimate set estimate, a novel uncertain set is introduced into the framework in order to house indices of variables that have been identified as being susceptible to cycling. The introduction of the uncertainty set guarantees convergence of the algorithm, and with techniques proposed to keep the set from expanding quickly, the practical performance of the algorithm is shown to be very efficient. Another PDAS variant is proposed for solving certain convex QPs that commonly arise when discretizing optimal control problems. The proposed framework allows inexactness in the subproblem solutions, which can significantly reduce computational cost in large-scale settings. By controlling the level inexactness either by exploiting knowledge of an upper bound of a matrix inverse or by dynamic estimation of such a value, the method achieves convergence guarantees and is shown to outperform a method that employs exact solutions computed by direct factorization techniques.Finally, the application of PDAS techniques for applications in statistics, variants are proposed for solving isotonic regression (IR) and trend filtering (TR) problems. It is shown that PDAS can solve an IR problem with n data points with only O(n) arithmetic operations. Moreover, the method is shown to outperform the state-of-the-art method for solving IR problems, especially when warm-starting is considered. Enhancements to themethod are proposed for solving general TF problems, and numerical results are presented to show that PDAS methods are viable for a broad class of such problems

Model Specification and Prediction in Joint Modelling

This thesis explores several methodological aspects of joint modelling of longitudinal outcomes and recurrent and terminal events, including variable selection, description, prediction, causal inference and model specification. The methods we discuss were motivated by the Community Ageing Research study (CARE75+) to investigate the relationships between frailty, falls and mortality. These outcomes have previously been analyzed with marginal models, but not as joint outcomes. We propose a variable selection strategy to optimize prediction of joint models for longitudinal and time-to-event outcomes. This strategy combines penalized likelihood with the LASSO penalty and cross-validation methods to select the fixed effects that optimize simultaneously the mean-squared error (MSE) and the Integrated Brier Score (IBS). Our simulation studies suggest that it is not always possible to optimize simultaneously MSE and IBS, but there seems to be a region defined by the constraints close to an optimal solution. In such a case a small compromise between MSE and IBS is required, depending on which outcome is the priority. Joint modelling has been an area of active research for description and prediction, but causal inference has received less attention. Using Direct Acyclic Graphs, we state our hypotheses about the paths between frailty, falls and mortality and confounders to formulate joint models adjusting for confounders. Via simulation studies we assessed the consequences of model misspecification, finding that even when link of the joint model and some features of the mean structure are not the correct ones, the fixed effects can still be correctly estimated

MATLAB

A well-known statement says that the PID controller is the "bread and butter" of the control engineer. This is indeed true, from a scientific standpoint. However, nowadays, in the era of computer science, when the paper and pencil have been replaced by the keyboard and the display of computers, one may equally say that MATLAB is the "bread" in the above statement. MATLAB has became a de facto tool for the modern system engineer. This book is written for both engineering students, as well as for practicing engineers. The wide range of applications in which MATLAB is the working framework, shows that it is a powerful, comprehensive and easy-to-use environment for performing technical computations. The book includes various excellent applications in which MATLAB is employed: from pure algebraic computations to data acquisition in real-life experiments, from control strategies to image processing algorithms, from graphical user interface design for educational purposes to Simulink embedded systems

Online learning of physics during a pandemic: A report from an academic experience in Italy

The arrival of the Sars-Cov II has opened a new window on teaching physics in academia. Frontal lectures have left space for online teaching, teachers have been faced with a new way of spreading knowledge, adapting contents and modalities of their courses. Students have faced up with a new way of learning physics, which relies on free access to materials and their informatics knowledge. We decided to investigate how online didactics has influenced students’ assessments, motivation, and satisfaction in learning physics during the pandemic in 2020. The research has involved bachelor (n = 53) and master (n = 27) students of the Physics Department at the University of Cagliari (N = 80, 47 male; 33 female). The MANOVA supported significant mean differences about gender and university level with higher values for girls and master students in almost all variables investigated. The path analysis showed that student-student, student-teacher interaction, and the organization of the courses significantly influenced satisfaction and motivation in learning physics. The results of this study can be used to improve the standards of teaching in physics at the University of Cagliar

Study on open science: The general state of the play in Open Science principles and practices at European life sciences institutes

Nowadays, open science is a hot topic on all levels and also is one of the priorities of the European Research Area. Components that are commonly associated with open science are open access, open data, open methodology, open source, open peer review, open science policies and citizen science. Open science may a great potential to connect and influence the practices of researchers, funding institutions and the public. In this paper, we evaluate the level of openness based on public surveys at four European life sciences institute

Space-time modelling of terrorism and counter-terrorism

In this thesis multiple approaches are presented which demonstrate the effectiveness of mathematical modelling to the study of terrorism and counter-terrorism strategies. In particular, theories of crime science are quantified to obtain objective outcomes. The layout of the research findings is in four parts. The first model studied is a Hawkes point process. This model describes events where past occurrence can lead to an increase in future events. In the context of this thesis a point process is used to capture dependence among terrorist attacks committed by the Provisional Irish Republican Army (PIRA) during ``The Troubles'' in Northern Ireland. The Hawkes process is adapted to produce a method capable of determining quantitatively temporally distinct phases within the PIRA movement. Expanding on the Hawkes model the next area of research introduces a time-varying background rate. In particular, using the Fast Fourier Transform a sinusoidal background rate is derived. This model then enables a study of seasonal trends in the attack profile of the Al Shabaab (AS) group. To study the spatial dynamics of terrorist activity a Dirichlet Process Mixture (DPM) model is examined. The DPM is used in a novel setting by considering the influence of improvised explosive device (IED) factory closures on PIRA attacks. The final research area studied in this thesis is data collection methods. An information retrieval (IR) tool is designed which can automatically obtain terrorist event details. Machine learning techniques are used to compare this IR data to a manually collected dataset. Future research ideas are introduced for each of the topics covered in this dissertation

Space station systems: A bibliography with indexes (supplement 10)

This bibliography lists 1,422 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to researchers, designers and managers engaged in Space Station technology development and mission design. Coverage includes documents that define major systems and subsystems related to structures and dynamic control, electronics and power supplies, propulsion, and payload integration. In addition, orbital construction methods, servicing and support requirements, procedures and operations, and missions for the current and future Space Station are included

Technology for large space systems: A bibliography with indexes (supplement 22)

This bibliography lists 1077 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to the researcher or manager engaged in the development of technologies related to large space systems. Subject areas include mission and program definition, design techniques, structural and thermal analysis, structural dynamics and control systems, electronics, advanced materials, assembly concepts, and propulsion

Proceedings of the Seventeenth Annual Conference on Manual Control

Manual control is considered, with concentration on perceptive/cognitive man-machine interaction and interface