A Parallel Riccati Factorization Algorithm with Applications to Model Predictive Control

Model Predictive Control (MPC) is increasing in popularity in industry as more efficient algorithms for solving the related optimization problem are developed. The main computational bottle-neck in on-line MPC is often the computation of the search step direction, i.e. the Newton step, which is often done using generic sparsity exploiting algorithms or Riccati recursions. However, as parallel hardware is becoming increasingly popular the demand for efficient parallel algorithms for solving the Newton step is increasing. In this paper a tailored, non-iterative parallel algorithm for computing the Riccati factorization is presented. The algorithm exploits the special structure in the MPC problem, and when sufficiently many processing units are available, the complexity of the algorithm scales logarithmically in the prediction horizon. Computing the Newton step is the main computational bottle-neck in many MPC algorithms and the algorithm can significantly reduce the computation cost for popular state-of-the-art MPC algorithms

Reduced Memory Footprint in Multiparametric Quadratic Programming by Exploiting Low Rank Structure

In multiparametric programming an optimization problem which is dependent on a parameter vector is solved parametrically. In control, multiparametric quadratic programming (mp-QP) problems have become increasingly important since the optimization problem arising in Model Predictive Control (MPC) can be cast as an mp-QP problem, which is referred to as explicit MPC. One of the main limitations with mp-QP and explicit MPC is the amount of memory required to store the parametric solution and the critical regions. In this paper, a method for exploiting low rank structure in the parametric solution of an mp-QP problem in order to reduce the required memory is introduced. The method is based on ideas similar to what is done to exploit low rank modifications in generic QP solvers, but is here applied to mp-QP problems to save memory. The proposed method has been evaluated experimentally, and for some examples of relevant problems the relative memory reduction is an order of magnitude compared to storing the full parametric solution and critical regions

Low-Rank Modifications of Riccati Factorizations for Model Predictive Control

In Model Predictive Control (MPC) the control input is computed by solving a constrained finite-time optimal control (CFTOC) problem at each sample in the control loop. The main computational effort is often spent on computing the search directions, which in MPC corresponds to solving unconstrained finite-time optimal control (UFTOC) problems. This is commonly performed using Riccati recursions or generic sparsity exploiting algorithms. In this work the focus is efficient search direction computations for active-set (AS) type methods. The system of equations to be solved at each AS iteration is changed only by a low-rank modification of the previous one, and exploiting this structured change is important for the performance of AS type solvers. In this paper, theory for how to exploit these low-rank changes by modifying the Riccati factorization between AS iterations in a structured way is presented. A numerical evaluation of the proposed algorithm shows that the computation time can be significantly reduced by modifying, instead of re-computing, the Riccati factorization. This speed-up can be important for AS type solvers used for linear, nonlinear and hybrid MPC

Issues relating to information and communication technology in middle schools in northern China with specific reference to two cities

The use of information and communications technology (ICT) in schools has become widespread in many countries throughout the world. The extent to which it has been incorporated into the work of schools varies widely from simply as a tool to help produce documents to one that is fully integrated into the whole school curriculum. Initiatives taken to encourage teaches to use ICT in their teaching and learning methodologies inevitably raise awareness of pedagogical issues and how these should be reappraised in the light of the demands of encompassing the new technology. China started the process of introducing ICT into its schools later than many other countries. This study examines the use of ICT in middle schools in cities in north east China to discover the attitudes of teachers and students to how effective the use of ICT is from their viewpoints. In addition the study ascertains the possibilities for further development of the use of ICT to enrich the students’ education. Where possible the interpretation of the analyses of the findings are generalised further from the two cities in which the survey took place.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Ethics and Globalisation: A Namibian Perspective - Ramatex Case

Globalisation can bring about many positive and negative changes to any economy. Namibia has enjoyed stability since gaining independence about 3 decades ago. Today, Namibia is struggling to stay afloat amid financial crisis. Numerous international companies such as Ramatex from Malaysia entered the business sphere shortly after independence, with promises to improve the livelihoods of a young economy. However, this only lasted for a very short while, as most of the promises were not met. As with many global companies, Ramatex packed up and left Namibia in less than 10 years. This had a very big impact on Namibia, as the economy had to find new ways to survive. A substantial number of citizens lost their jobs, and the psychological impacts of recovery were very detrimental on the families. Namibians from all across the country flocked to the capital city Windhoek, with the aim of improving their lives, but all these dreams, hopes and aspirations were short lived. This chapter will make use of secondary research documents and in-depth interviews with some of the key stakeholders. On a positive side, the closure of Ramatex led to the birth local manufacturing giant Dinapama Manufacturing and Supplies, which is striving using lessons from the past to build capacity in the local economy

Empowering Namibian Indigenous People through Entrepreneurship: The Case from the Nama People

The challenge emanating from the colonial and apartheid regimes on the Nama people of Namibia have not only resulted in them losing nearly half of its population, but they also appeared to have lost their social identity. To that end we continually find convergences and divergences in clothing and accessories, food, traditional dances, homes, and traditional beauty cosmetics, between the past and present. This chapter seeks to explore whether the Nama people have always used money to acquire the aforementioned past? If not, what have they done right in the past to acquire all these items? These are one of the few questions this chapter seeks to explore and understand, and the role Nama entrepreneurial activities play for their own socio-economic advancement. Critical discourse can lead to a better understanding and appreciation of entrepreneurship among indigenous people in Namibia. This will in turn result in an enhanced understanding of the role entrepreneurship and culture can play in both a local and international context. After a brief introduction to Namibia and the Nama people, the cultural values and entrepreneurial initiatives of the Nama people are discussed, followed by discussions, recommendations and conclusions. Research methods employed were in-depth interviews and participant observation

Creating pseudo-tactile feedback in virtual reality using shared crossmodal properties of audio and tactile feedback

Virtual reality has the potential to enhance a variety of real-world training and entertainment applications by creating the illusion that a user of virtual reality is physically present inside the digitally created environment. However, the use of tactile feedback to convey information about this environment is often lacking in VR applications. New methods for inducing a degree of tactile feedback in users are described, which induced the illusion of a tactile experience, referred to as pseudo-tactile feedback. These methods utilised shared properties between audio and tactile feedback that can be crossmodally mapped between the two modalities in the design of a virtual reality prototype for a qualitative usability study in order to test the effectiveness and underlying causes of such feedback in the total absence of any real-world tactile feedback. Results show that participants required believable audio stimuli that they could conceive as real-world textures as well a sense of hand-ownership to suspend disbelief and construct an internally consistent mental model of the virtual environment. This allowed them to conceive believable tactile sensations that result from interaction with virtual objects inside this environment.http://sacj.cs.uct.ac.zaInformation Scienc

Virtual and Augmented Reality for Environmental Sustainability: A Systematic Review

In recent years, extended reality (XR) technology has seen a rise in use in environmental subjects, i.e., climate change or biodiversity loss, as a potential tool to inform and engage the public with current and future environmental issues. However, research on the potential of XR technology for environmental sustainability is still in the early stages, and there is no clear synthesis of the methods studied in this field. To provide a clearer view of existing approaches and research objectives, we systematically reviewed current literature dealing with XR use in environmental topics. Although the results indicate that the volume of literature exploring XR in environmental applications is increasing, empirical evidence of its impact is limited, hindering the possibility of presently drawing significant conclusions on its potential benefits. Based on our analyses, we identified thematic, theoretical, and methodological knowledge gaps and provide a guideline to aid future research in the field.Peer reviewe

The HETDEX Survey: Emission Line Exploration and Source Classification

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the Universe at $z \sim 2.4$ to 1% precision for both $H(z)$ and $D_A(z)$. HETDEX is in the process of mapping in excess of one million Lyman Alpha emitting (LAE) galaxies and a similar number of lower-z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly$\alpha$ emission from the lower-$z$ interloping galaxies, primarily [OII], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Angstrom rest-frame equivalent width cut commonly used to distinguish LAEs from lower-$z$ [OII] emitting galaxies. Despite a spectral resolving power, R $\sim800$, that cannot resolve the [OII] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly$\alpha$ by [OII] of 1.2% and a Ly$\alpha$ recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements.Comment: 38 pages, 11 figure