A Global Communication Optimization Technique Based on Data-Flow Analysis and Linear Algebra

Reducing communication overhead is extremely important in distributed-memory message-passing architectures. In this paper, we present a technique to improve communication that considers data access patterns of the entire program. Our approach is based on a combination of traditional data-flow analysis and a linear algebra framework, and works on structured programs with conditional statements and nested loops but without arbitrary goto statements. The distinctive features of the solution are the accuracy in keeping communication set information, support for general alignments and distributions including block-cyclic distributions and the ability to simulate some of the previous approaches with suitable modifications. We also show how optimizations such as message vectorization, message coalescing and redundancy elimination are supported by our framework. Experimental results on several benchmarks show that our technique is effective in reducing the number of messages (an average of 32% reduction), the volume of the data communicated (an average of 37% reduction), and the execution time (an average of 26% reduction)

HDArray: Parallel Array Interface for Distributed Heterogeneous Devices

Heterogeneous clusters with nodes containing one or more accelerators, such as GPUs, have become common. While MPI provides a mechanism and management of interaddress space communication, and OpenCL provides a way to manage computation and communication within a process with access to heterogeneous computational resources, programmers are forced to write hybrid programs that manage the interaction of both of these systems. This paper describes an array programming interface that provides users with automatic or manual distributions of data and work. Using the distribution and information about what data is used and defined by kernels, communication among processes and among devices in a process is performed automatically. The interface provides a unified programming model to the user, thus simplifying program development

Raising Household Leverage: Evidence from Co-Financed Mortgages

This article studies the impact on mortgage origination conditions and performance of a product that aims at raising household leverage: bank mortgages co-financed with a housing provident fund (HPF), a compulsory saving scheme for all private sector workers in Mexico. Relative to traditional bank mortgages, our estimates show that down payment of the co-financed declines substantially, by 7.6 percentage points, whereas purchased properties are not more expensive. Despite their higher leverage, co-financed bank mortgages do not exhibit higher default rates---their lower liquidity needs to cover upfront costs and monthly payments reduce credit risk. We also find distributional effects: The scheme alleviates borrowing constraints more at lower incomes, especially when banks are smaller. Larger banks, with a greater share of low-income borrowers, use co-financing to reduce the amount lent to those segments. Thus, when the HPF's lending conditions become relatively less generous at lower incomes, we find that larger banks neutralize the substitution between traditional and co-financed mortgages that is found on smaller banks' portfolios

Runtime Coupling of Data-parallel Programs

We consider the problem of efficiently coupling multiple data-parallel programs at runtime. We propose an approach that establishes a mapping between data structures in different data-parallel programs and implements a user specified consistency model. Mappings are established at runtime and new mappings between programs can be added and deleted while the programs are in execution. Mappings, or the identity of the processors involved, do not have to be known at compile-time or even link-time. Programs can be made to interact with different granularities of interaction without requiring any re-coding. A priori knowledge of data movement requirements allows for buffering of data and overlap of computations between coupled applications. Efficient data movement is achieved by pre-computing an optimized schedule. We describe our prototype implementation and evaluate its performance for a set of synthetic benchmarks that examine the variation of performance with coupling parameters. We demonstrate that the cost of the added flexibility gained by our coupling method is not prohibitive when compared with a monolithic code that does the same computation. (Also cross-referenced as UMIACS-TR-95-116

Compiler Techniques for Optimizing Communication and Data Distribution for Distributed-Memory Computers

Advanced Research Projects Agency (ARPA)National Aeronautics and Space AdministrationOpe

Spread spectrum-based video watermarking algorithms for copyright protection

Merged with duplicate record 10026.1/2263 on 14.03.2017 by CS (TIS)Digital technologies know an unprecedented expansion in the last years. The consumer can now benefit from hardware and software which was considered state-of-the-art several years ago. The advantages offered by the digital technologies are major but the same digital technology opens the door for unlimited piracy. Copying an analogue VCR tape was certainly possible and relatively easy, in spite of various forms of protection, but due to the analogue environment, the subsequent copies had an inherent loss in quality. This was a natural way of limiting the multiple copying of a video material. With digital technology, this barrier disappears, being possible to make as many copies as desired, without any loss in quality whatsoever. Digital watermarking is one of the best available tools for fighting this threat. The aim of the present work was to develop a digital watermarking system compliant with the recommendations drawn by the EBU, for video broadcast monitoring. Since the watermark can be inserted in either spatial domain or transform domain, this aspect was investigated and led to the conclusion that wavelet transform is one of the best solutions available. Since watermarking is not an easy task, especially considering the robustness under various attacks several techniques were employed in order to increase the capacity/robustness of the system: spread-spectrum and modulation techniques to cast the watermark, powerful error correction to protect the mark, human visual models to insert a robust mark and to ensure its invisibility. The combination of these methods led to a major improvement, but yet the system wasn't robust to several important geometrical attacks. In order to achieve this last milestone, the system uses two distinct watermarks: a spatial domain reference watermark and the main watermark embedded in the wavelet domain. By using this reference watermark and techniques specific to image registration, the system is able to determine the parameters of the attack and revert it. Once the attack was reverted, the main watermark is recovered. The final result is a high capacity, blind DWr-based video watermarking system, robust to a wide range of attacks.BBC Research & Developmen

The Role of Sox4 in Ocular Morphogenesis and Retinal Differentiation

Visual impairment ranges from mild forms that can be corrected with glasses to more severe cases that result in permanent loss of vision. Microphthalmia, anophthalmia, and coloboma (collectively referred to as MAC) account for 11% of cases of pediatric blindness and are a result of improper ocular morphogenesis. Retinitis Pigmentosa (RP) is a retinal degenerative disease that affects 1 in 3000 people worldwide. It is a progressive disorder that initially begins with loss of vision in low light settings due to rod photoreceptor degeneration but progresses to complete blindness upon loss of cone photoreceptors. Currently, there is no cure for either MAC or RP. Further insight into the essential components of ocular morphogenesis and the generation of retinal neurons could provide the base of knowledge needed for better patient screening and treatments like cell therapies. The transcription factor Sox4 has previously been implicated as an important factor in both ocular morphogenesis and retinal development. Studies in humans, mice, zebrafish, and Xenopus have all linked Sox4 to microphthalmia and coloboma. Additional studies suggest a role for Sox4 in the generation of specific retinal neurons. Interestingly, in zebrafish, the absence of maternal sox4 transcripts in the developing embryo results in both microphthalmia and a reduction of rod photoreceptors. This suggests that Sox4 has a critical role early in specification of the eyefield that influences later retinal differentiation, however the precise functions of Sox4 during vertebrate ocular morphogenesis and retinal cell type differentiation remain unclear. The studies presented in this Dissertation provide new insights into the role of Sox4 in eye development. Chapter 1 of this dissertation presents a review of ocular morphogenesis, retinal development, and what is currently known about the function of SoxC transcription factors and particularly Sox4 in embryonic and ocular development. In Chapter 2, a method to visualize ocular morphogenesis in living zebrafish embryos with high spatial and temporal resolution is demonstrated. Chapter 3 describes a detailed characterization of the ocular phenotypes of zebrafish sox4 mutants, and an in-depth analysis into the role Sox4 plays in both ocular morphogenesis and retinal differentiation. In vivo time lapse imaging, assays to assess cell proliferation and cell death, and immunohistochemistry to detect retinal cell types were used to characterize the phenotypes of microphthalmia and a reduction of rod photoreceptors in the sox4 mutants. Furthermore, scRNA-seq was used to address if there is any heterogeneity prior to ocular morphogenesis that may affect later retinal differentiation. Chapter 4 will address the impact of findings in the sox4 mutants, and the suggested future directions for this project. Finally, an appendix chapter will include additional data about a possible role for Sox4 in neural crest cells