Distributed Maple: parallel computer algebra in networked environments

AbstractWe describe the design and use of Distributed Maple, an environment for executing parallel computer algebra programs on multiprocessors and heterogeneous clusters. The system embeds kernels of the computer algebra system Maple as computational engines into a networked coordination layer implemented in the programming language Java. On the basis of a comparatively high-level programming model, one may write parallel Maple programs that show good speedups in medium-scaled environments. We report on the use of the system for the parallelization of various functions of the algebraic geometry library CASA and demonstrate how design decisions affect the dynamic behaviour and performance of a parallel application. Numerous experimental results allow comparison of Distributed Maple with other systems for parallel computer algebra

Informal economic activities in Ghana: a case study of slums in Kumasi and Accra.

Doctor of Philosophy in Economics.University of KwaZulu-Natal, Pietermaritzburg, 2016.Slums are urban households, which lack permanently durable housing, adequate living space, access to clean water, suitable sanitation and land tenure security. Globally, slums house a third of the world’s population. These slums do not only accommodate individuals who cannot afford formal housing, but also, a vibrant informal sector. Slum operators engage in diverse economic activities to earn a living, mostly in cities where there is lack of employment opportunities. Slum activities are an integral part of the informal sector, which globally, is found to contribute significantly to employment and income, especially among low-skill individuals. In Ghana, the informal sector employs 86% of the total labour force. The Harris-Todaro model suggests that people migrate from rural to urban areas because of income differentials and employment opportunities. In the absence of adequate housing and employment facilities in Ghana, migration results in the growth of slums and urban slum informal activities as people look for a place to stay and earn a living in desperation. The informal sector is a flourishing segment of the economy, a springboard from which many dynamic small firms may graduate to the formal sector over time. There may be other motivations too that influence people in Ghana to engage in the informal slum activity. This study examined what factors motivate individuals to engage in that sector on the basis of a survey of 344 slum operators in Kumasi and Accra, two major cities in Ghana. Data collected by means of a questionnaire were analysed using SPSS and STATA. The study found out that, three levels are involved when one engages in slum activities; the entry, operation and exit phases. Factors that motivate operators to engage in slum activities represent the first stage. Using Principal Component Analysis, the study found out that avoidance of government regulation is the main motive for one’s involvement in slum activities. Hence, government initiatives that will take away some of the bureaucratic burdens and rigorous procedures of operating in the formal sector may assist in reducing the growth rate of slum activities in Ghana. Other driving forces include the ‘luxury’ of working at one’s own time, making use of one’s talents and relations, and the quest for higher income. An operator’s participation in slum activities represents the second stage. As one engages in these economic activities to generate income, the study found out that, the surveyed operators earn about US $8 a day, higher than the World Bank’s poverty line of US$2 a day. To find out what factors determine the average daily income earned, the OLS regression analysis is used. Amongst factors, iii an operator’s social networks, locus of control, type of economic activity, educational level, age of business and labour size, it was found that firm age was the main determinant of average daily income in slum activities in Ghana, with a 20% increase in average daily income for every extra year of operation. Some hypotheses are also tested regarding differences in performance between the two regions and between male and female operators. The mean income of males is found to be significantly higher than that of females while differences in average income are also found between the two regions. The study then investigated the constraints that limit the growth and development of enterprises, using Factor Analysis. Of the constraints, insufficient skills and business knowledge was most inhibiting. Other growth constraints include infrastructural challenges, difficulty in accessing credit, lack of tools and materials, security problems, poor communication and social networking. Exiting informal slum activities represents the third and final stage, which involves a slum operator’s willingness to move into formal activities. Formalising of the informal sector is crucial to generating sustainable income and employment. Results from logistic regression indicate that of all the constraints, addressing access to finance will prompt slum operators to move into formal sector. Many slum operators are happy to stay in the informal sector. Nevertheless, it is imperative that policy makers come up with suitable financing strategies to assist slum operators in order to help in formalisation

Parallel simulation of volume-coupled multi-field problems with special application to soil dynamics

Zur Lösung vieler ingenieur- und naturwissenschaftlichen Problemstellungen sind numerische Simulationen ein wichtiges Hilfsmittel. Sie dienen beispielsweise der Wettervorhersage in der Meteorologie oder der Strukturanalyse und Strukturoptimierung im Maschinenbau. In vielen Aufgabenstellungen kann das untersuchte Problem, aufgrund seiner starken Wechselwirkung mit den angrenzenden Systemen, nicht losgelöst betrachtet werden, so dass eine gesamtheitliche Betrachtungsweise notwendig wird. Diese Systeme werden in der Literatur als gekoppelte Probleme bezeichnet. Aufgrund der Komplexität der betrachteten Probleme sind zur effizienten Lösung der zugrunde liegenden Gleichungen parallele Lösungsstrategien von Vorteil. Hierbei wird das Gesamtproblem in kleinere Teilprobleme zerlegt, die gleichzeitig auf verschiedenen Rechnern oder Prozessoren gelöst werden. Um die Vorteile dieses Lösungsverfahrens bestmöglich nutzen zu können, sind erhebliche Anstrengungen zunächst für die initiale Entwicklung und Umsetzung eines effizienten Lösungsverfahrens sowie anschließend für dessen kontinuierliche Weiterentwicklung notwendig. Die vorliegende Monographie beschreibt einen Ansatz zur Kosimulation numerischer Probleme zwischen dem kommerziellen auf der Finite-Elemente-Methode (FEM) basierenden Programmpaket Abaqus und dem für die Forschung entwickelten Löser PANDAS. Durch die Entwicklung einer allgemeinen Schnittstelle können die Materialmodelle von PANDAS direkt, ohne eine langwierige und fehleranfällige Reimplementierung, in eine für die industrielle Anwendung wichtige Simulationsumgebung überführt werden. Hierbei kann direkt auf die umfangreiche Materialmodellbibliothek von PANDAS zurückgegriffen werden. Zur Illustration der Anwendungsmöglichkeiten der Abaqus-PANDAS-Kopplung wird diese exemplarisch zur Simulation verschiedener volumengekoppelter Mehrfeldprobleme herangezogen. Als bodenmechanisches Anwendungsbeispiel wird die Tragfähigkeit eines flüssigkeitgesättigten granularen Materials unter quasi-statischen und dynamischen zyklischen Belastungen untersucht. Weiterhin werden mehrphasige Strömungsprozesse, wie sie z. B. im Produktionsprozess von faserverstärkten Kunststoffen auftreten, numerisch simuliert. Im sogenannten Vaccum-Assisted-Resin-Transfer-Moulding (VARTM), wird ein zunächst trockenes (gasgesättigtes) Fasergewebe kontinuierlich mit Harz getränkt, wobei für die praktische Anwendung insbesondere die Zeit bis zur vollständigen Sättigung und der sich einstellende Faservolumenanteil im fertigen Bauteil von großem Interesse sind. Weiterhin werden die Effizienz und die parallele Skalierbarkeit des vorgeschlagenen Kosimulationsansatzes untersucht

Education and economic growth in Indonesia

Ph.DDOCTOR OF PHILOSOPH