Sorting Integers on the AP1000

Sorting is one of the classic problems of computer science. Whilst well understood on sequential machines, the diversity of architectures amongst parallel systems means that algorithms do not perform uniformly on all platforms. This document describes the implementation of a radix based algorithm for sorting positive integers on a Fujitsu AP1000 Supercomputer, which was constructed as an entry in the Joint Symposium on Parallel Processing (JSPP) 1994 Parallel Software Contest (PSC94). Brief consideration is also given to a full radix sort conducted in parallel across the machine.Comment: 1994 Project Report, 23 page

Parallel alogorithms for MIMD parallel computers

This thesis mainly covers the design and analysis of asynchronous parallel algorithms that can be run on MIMD (Multiple Instruction Multiple Data) parallel computers, in particular the NEPTUNE system at Loughborough University. Initially the fundamentals of parallel computer architectures are introduced with different parallel architectures being described and compared. The principles of parallel programming and the design of parallel algorithms are also outlined. Also the main characteristics of the 4 processor MIMD NEPTUNE system are presented, and performance indicators, i.e. the speed-up and the efficiency factors are defined for the measurement of parallelism in a given system. Both numerical and non-numerical algorithms are covered in the thesis. In the numerical solution of partial differential equations, a new parallel 9-point block iterative method is developed. Here, the organization of the blocks is done in such a way that each process contains its own group of 9 points on the network, therefore, they can be run in parallel. The parallel implementation of both 9-point and 4- point block iterative methods were programmed using natural and redblack ordering with synchronous and asynchronous approaches. The results obtained for these different implementations were compared and analysed. Next the parallel version of the A.G.E. (Alternating Group Explicit) method is developed in which the explicit nature of the difference equation is revealed and exploited when applied to derive the solution of both linear and non-linear 2-point boundary value problems. Two strategies have been used in the implementation of the parallel A.G.E. method using the synchronous and asynchronous approaches. The results from these implementations were compared. Also for comparison reasons the results obtained from the parallel A.G.E. were compared with the ~ corresponding results obtained from the parallel versions of the Jacobi, Gauss-Seidel and S.O.R. methods. Finally, a computational complexity analysis of the parallel A.G.E. algorithms is included. In the area of non-numeric algorithms, the problems of sorting and searching were studied. The sorting methods which were investigated was the shell and the digit sort methods. with each method different parallel strategies and approaches were used and compared to find the best results which can be obtained on the parallel machine. In the searching methods, the sequential search algorithm in an unordered table and the binary search algorithms were investigated and implemented in parallel with a presentation of the results. Finally, a complexity analysis of these methods is presented. The thesis concludes with a chapter summarizing the main results

Data access pattern protection in cloud storage

Cloud-based storage service has been popular nowadays. Due to the convenience and unprecedent cost-effectiveness, more and more individuals and organizations have utilized cloud storage servers to host their data. However, because of security and privacy concerns, not all data can be outsourced without reservation. The concerns are rooted from the users\u27 loss of data control from their hands to the cloud servers\u27 premise and the infeasibility for them to fully trust the cloud servers. The cloud servers can be compromised by hackers, and they themselves may not be fully trustable. As found by Islam et. al.~\cite{Islam12}, data encryption alone is not sufficient. The server is still able to infer private information from the user\u27s {\em access pattern}. Furthermore, it is possible for an attacker to use the access pattern information to construct the data query and infer the plaintext of the data. Therefore, Oblivious RAMs (ORAM) have been proposed to allow a user to access the exported data while preserving user\u27s data access pattern. In recent years, interests in ORAM research have increased, and many ORAM constructions have been proposed to improve the performance in terms of the communication cost between the user and the server, the storage costs at the server and the user, and the computational costs at the server and the user. However, the practicality of the existing ORAM constructions is still questionable: Firstly, in spite of the improvement in performance, the existing ORAM constructions still require either large bandwidth consumption or storage capacity. %in practice. Secondly, these ORAM constructions all assume a single user mode, which has limited the application to more general, multiple user scenarios. In this dissertation, we aim to address the above limitations by proposing four new ORAM constructions: S-ORAM, which adopts piece-wise shuffling and segment-based query techniques to improve the performance of data shuffling and query through factoring block size into design; KT-ORAM, which organizes the server storage as a $k$-ary tree with each node acting as a fully-functional PIR storage, and adopts a novel delayed eviction technique to optimize the eviction process; GP-ORAM, a general partition-based ORAM that can adapt the number of partitions to the available user-side storage and can outsource the index table to the server to reduce local storage consumption; and MU-ORAM, which can deal with stealthy privacy attack in the application scenarios where multiple users share a data set outsourced to a remote storage server and meanwhile want to protect each individual\u27s data access pattern from being revealed to one another. We have rigorously quantified and proved the security strengths of these constructions and demonstrated their performance efficiency through detailed analysis

Dynamic diffracting trees

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 109-111).by Giovanni M. Della-Libera.M.Eng

Analysis and design of parallel algorithms

The present state of electronic technology is such that factors affecting computation speed have almost been minimised; switching for instance is almost instantaneous. Electronic components are so good, in fact, that the time taken for a logic signal to travel between two points is now a significant factor of instruction times. Clearly, with the actual physical size of components being very small and the high circuit density, there is little scope for improving computation speech significantly by such means as even denser circuitry or still faster electronic components. Thus, development of faster computers will require a new approach that depends on the imaginative use of existing knowledge. One such approach is to increase computation speed through parallelism. Obviously, a parallel computer with p identical processors is potentially p times as fast as a single computer, although this limit can rarely be achieved

Future Computer Requirements for Computational Aerodynamics

Recent advances in computational aerodynamics are discussed as well as motivations for and potential benefits of a National Aerodynamic Simulation Facility having the capability to solve fluid dynamic equations at speeds two to three orders of magnitude faster than presently possible with general computers. Two contracted efforts to define processor architectures for such a facility are summarized