Massively parallel approximate Gaussian process regression

We explore how the big-three computing paradigms -- symmetric multi-processor (SMC), graphical processing units (GPUs), and cluster computing -- can together be brought to bare on large-data Gaussian processes (GP) regression problems via a careful implementation of a newly developed local approximation scheme. Our methodological contribution focuses primarily on GPU computation, as this requires the most care and also provides the largest performance boost. However, in our empirical work we study the relative merits of all three paradigms to determine how best to combine them. The paper concludes with two case studies. One is a real data fluid-dynamics computer experiment which benefits from the local nature of our approximation; the second is a synthetic data example designed to find the largest design for which (accurate) GP emulation can performed on a commensurate predictive set under an hour.Comment: 24 pages, 6 figures, 1 tabl

Application of supercomputers to computational aerodynamics

Computers are playing an increasingly important role in the field of aerodynamics such that they now serve as a major complement to wind tunnels in aerospace research and development. Factors pacing advances in computational aerodynamics are identified, including the amount of computational power required to take the next major step in the discipline. Example results obtained from the successively refined forms of the governing equations are discussed, both in the context of levels of computer power required and the degree to which they either further the frontiers of research or apply to problems of practical importance. Finally, the Numerical Aerodynamic Simulation (NAS) Program - with its 1988 target of achieving a sustained computational rate of 1 billion floating point operations per second and operating with a memory of 240 million words - is discussed in terms of its goals and its projected effect on the future of computational aerodynamics

Flexible working policies and environments in UK Local Authorities: current practice

The research surveys the uptake of 'modern' or flexible working practices in UK Local Authorities, especially as it impacts on property and office accommodation. Nearly all permit flexible starting and finishing times for as many employees as is practical while forms of accredited hours working for at least some appropriate employees are policy in a majority. Flexible practices with property and ICT implications, working from home without a dedicated work station, formal policies, 'hot' desking, flexible offices and satellite or drop-in offices are less common (ca 10%) but have grown significantly in the last two years. A number of councils also report being at the stage of planning pilots. Five detailed case studies are reported. Three authorities have expanding strategic programmes for 'workstyle' changes or new ways of working. One has shifted its emphasis away from such plans toward higher density office usage only and one was awaiting the election result before anticipated permission to start. These cases do all come from authorities in areas of much higher than average property values and costs. While they have seen savings, they emphasise that the initiatives were equally about better work life balance and improved office environments. Green benefits and service enhancements are harder to quantify but are believed to have been achieved. Higher density of net space utilisation has uniformly been achieved. Executive commitment and clear member support are seen as critical strategic success factors. Clear liaison between HR, Property/ Facilities and ICT has been essential to operational success. Entrenched management attitudes and, at least initially, staff reluctance to change, are cited as the major drawbacks. Accounting and valuation practices can also be a barrier. Similar messages are provided by a variety of pilots, some undertaken deliberately as strategic tests, others as much more of an ad hoc response to local circumstances. Most have not, or not yet, seen net office space reduced. The more successful pilots were not 'just' either property or HR policy initiatives: indeed there is some evidence that initiatives involving only one of the two functions have been less successful. Service areas most frequently cited as being involved in changes are various property functions. Trading Standards and Social Services are other areas where the real or potential development of flexible working and shared desking is highlighted though the latter in particular is also cited as an area where workers in the office have particular mutual support needs. Higher density officing for less mobile workers is, in principle, an option more widely available. Workplace strategy should reflect future service delivery models, asset management plans and organisational development. New ways of working have been a tool for achieving changes in culture and delivery, but were, and are, a challenge to traditional mindsets. They will involve senior property professionals in a range of issues with which they have not traditionally been associated. Future property and workplace strategy will be driven by an authority's service models and aspirations as to working culture: but will also be a tool, alongside organisational development (OD) and ICT, to achieve change and improvement

Throughput analysis in manufacturing networds [sic]

"December 1990."Includes bibliographical references.Research partially supported by the Leaders for Manufacturing Program.by Gabriel R. Bitran, Deb Sarkar

A review of GIS-based information sharing systems

GIS-based information sharing systems have been implemented in many of England and Wales' Crime and Disorder Reduction Partnerships (CDRPs). The information sharing role of these systems is seen as being vital to help in the review of crime, disorder and misuse of drugs; to sustain strategic objectives, to monitor interventions and initiatives; and support action plans for service delivery. This evaluation into these systems aimed to identify the lessons learned from existing systems, identify how these systems can be best used to support the business functions of CDRPs, identify common weaknesses across the systems, and produce guidelines on how these systems should be further developed. At present there are in excess of 20 major systems distributed across England and Wales. This evaluation considered a representative sample of ten systems. To date, little documented evidence has been collected by the systems that demonstrate the direct impact they are having in reducing crime and disorder, and the misuse of drugs. All point to how they are contributing to more effective partnership working, but all systems must be encouraged to record how they are contributing to improving community safety. Demonstrating this impact will help them to assure their future role in their CDRPs. By reviewing the systems wholly, several key ingredients were identified that were evident in contributing to the effectiveness of these systems. These included the need for an effective partnership business model within which the system operates, and the generation of good quality multi-agency intelligence products from the system. In helping to determine the future development of GIS-based information sharing systems, four key community safety partnership business service functions have been identified that these systems can most effectively support. These functions support the performance review requirements of CDRPs, operate a problem solving scanning and analysis role, and offer an interface with the public. By following these business service functions as a template will provide for a more effective application of these systems nationally

MATEX: A Distributed Framework for Transient Simulation of Power Distribution Networks

We proposed MATEX, a distributed framework for transient simulation of power distribution networks (PDNs). MATEX utilizes matrix exponential kernel with Krylov subspace approximations to solve differential equations of linear circuit. First, the whole simulation task is divided into subtasks based on decompositions of current sources, in order to reduce the computational overheads. Then these subtasks are distributed to different computing nodes and processed in parallel. Within each node, after the matrix factorization at the beginning of simulation, the adaptive time stepping solver is performed without extra matrix re-factorizations. MATEX overcomes the stiff-ness hinder of previous matrix exponential-based circuit simulator by rational Krylov subspace method, which leads to larger step sizes with smaller dimensions of Krylov subspace bases and highly accelerates the whole computation. MATEX outperforms both traditional fixed and adaptive time stepping methods, e.g., achieving around 13X over the trapezoidal framework with fixed time step for the IBM power grid benchmarks.Comment: ACM/IEEE DAC 2014. arXiv admin note: substantial text overlap with arXiv:1505.0669

Breaking Instance-Independent Symmetries In Exact Graph Coloring

Code optimization and high level synthesis can be posed as constraint satisfaction and optimization problems, such as graph coloring used in register allocation. Graph coloring is also used to model more traditional CSPs relevant to AI, such as planning, time-tabling and scheduling. Provably optimal solutions may be desirable for commercial and defense applications. Additionally, for applications such as register allocation and code optimization, naturally-occurring instances of graph coloring are often small and can be solved optimally. A recent wave of improvements in algorithms for Boolean satisfiability (SAT) and 0-1 Integer Linear Programming (ILP) suggests generic problem-reduction methods, rather than problem-specific heuristics, because (1) heuristics may be upset by new constraints, (2) heuristics tend to ignore structure, and (3) many relevant problems are provably inapproximable. Problem reductions often lead to highly symmetric SAT instances, and symmetries are known to slow down SAT solvers. In this work, we compare several avenues for symmetry breaking, in particular when certain kinds of symmetry are present in all generated instances. Our focus on reducing CSPs to SAT allows us to leverage recent dramatic improvement in SAT solvers and automatically benefit from future progress. We can use a variety of black-box SAT solvers without modifying their source code because our symmetry-breaking techniques are static, i.e., we detect symmetries and add symmetry breaking predicates (SBPs) during pre-processing. An important result of our work is that among the types of instance-independent SBPs we studied and their combinations, the simplest and least complete constructions are the most effective. Our experiments also clearly indicate that instance-independent symmetries should mostly be processed together with instance-specific symmetries rather than at the specification level, contrary to what has been suggested in the literature