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Multiway merging in parallel

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IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 1996年第1期7卷 11-17页

作者： Wen, ZF Hewlwtt-Packard Convex Technology Center Richardson TX USA

The problem of merging k (k greater than or equal to 2) sorted lists is considered. We give an optimal parallel algorithm which takes O(n log k/p + log n) time using p processors on a parallel random access machine that allows concurrent reads and exclusive writes, where n is the total size of the input lists. This algorithm achieves O(log n) time using p = n log k/log n processors. Most of the previous research for this problem has been focused on the case when k = 2. Very recently, parallel solutions for the case when k > 2 have been reported. Our solution is the first logarithmic time optimal parallel algorithm for the problem when k greater than or equal to 2. It can also be seen as a unified optimal parallel algorithm for sorting and merging. In order to support the algorithm, a new processor assignment strategy is also presented.

关键词： analysis of algorithms databases information retrieval merging parallel computation processors assignment sorting

Design considerations for air cooling electronic systems in high altitude conditions

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Design considerations for air cooling electronic systems in ...

IEEE Symposium on Semiconductor Thermal Measurement and Management (SEMI-THERM)

作者： C.L. Belady Convex Technology Center Hewlett Packard Company Richardson TX USA

Covers the impact of altitude on electronics cooling. MIL-STD 210 is reviewed to demonstrate the relationship of altitude to density as well as to outside air temperature. Once these relationships are understood the paper discusses the impact of altitude on the performance of air moving devices using the widely accepted fan laws. A discussion of both constant speed and altitude compensating fans addresses performance issues such as power dissipation, pressure drop, and free delivery of fans under these conditions. Once the fan performance has been characterized, the system impedance (or pressure drop) must be determined for the appropriate altitude. The paper covers how system impedance changes under laminar and turbulent flow regimes as altitude varies. This is most important since poor thermal designs have resulted when the flow regime was not known. Since every altitude has a unique system impedance, a modified system impedance curve, called the Sigma-Delta P curve, is presented. This collapses all of the altitude curves to one curve and is a powerful way to characterize a system for all altitudes. The impact of altitude on heat transfer is also discussed along with the effects of operating in the turbulent and laminar regimes. In order to demonstrate the concepts, an example problem is worked.

关键词： Electronics cooling Fans Impedance Ocean temperature Heat transfer Temperature dependence Power dissipation Delta-sigma modulation Aerospace electronics Sea level

RECONSTRUCTING TRIANGLES INSCRIBED IN convex BODIES FROM X-RAY FUNCTIONS

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Acta Mathematica Scientia 2004年第4期24卷 608-612页

作者：熊革李德宜 Department of Mathematics Shanghai University Shanghai 200436 China Department of Mathematics Wuhan University of Science and Technology Wuhan 430081 Chinahis paper provides a method using fixed-point theory for the reconstruction of the triangle inscribed in convex bodies from X-ray functions in three arbitrary mutual directions.

This paper provides a method using fixed-point theory for the reconstruction of the triangle inscribed in convex bodies from X-ray functions in three arbitrary mutual directions.

关键词： convex body X-ray reconstruction

Issues on the architecture and the design of distributed shared memory systems

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Issues on the architecture and the design of distributed sha...

IEEE International Conference on Computer Design: VLSI in Computers and Processors, (ICCD)

作者： Nian-Feng Tzeng S.J. Wallach Center for Advanced Computer Studies University of Southwestern Louisiana Lafayette USA Convex Technology Hewlett Packard Company Richardson TX USA

Distributed shared memory (DSM) systems could overcome major obstacles of the widespread use of distributed-memory multiprocessors, while retaining the attractive features of low cost and good scalability common to distributed-memory machines. A DSM system allows a natural and portable programming model on distributed-memory machines, making it possible to construct a relatively inexpensive and scalable parallel system on which programmers can develop parallel application codes. Due to its potential advantages, DSM has received increasing attention. In this panel, challenges in building efficient DSM systems for a wide range of applications are addressed and discussed.

关键词： Costs Hardware Scalability Computer networks Programming profession Space technology Electronic mail Parallel programming Buildings Distributed computing

FDR-Controlled Portfolio Optimization for Sparse Financial Index Tracking

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arXiv 2024年

作者： Machkour, Jasin Palomar, Daniel P. Muma, Michael The Robust Data Science Group Technische Universität Darmstadt Germany The Convex Optimization Group The Hong Kong University of Science and Technology Hong Kong

In high-dimensional data analysis, such as financial index tracking or biomedical applications, it is crucial to select the few relevant variables while maintaining control over the false discovery rate (FDR). In these applications, strong dependencies often exist among the variables (e.g., stock returns), which can undermine the FDR control property of existing methods like the model-X knockoff method or the T-Rex selector. To address this issue, we have expanded the T-Rex framework to accommodate overlapping groups of highly correlated variables. This is achieved by integrating a nearest neighbors penalization mechanism into the framework, which provably controls the FDR at the user-defined target level. A real-world example of sparse index tracking demonstrates the proposed method's ability to accurately track the S&P 500 index over the past 20 years based on a small number of stocks. An open-source implementation is provided within the R package TRexSelector on CRAN. Copyright © 2024, The Authors. All rights reserved.

关键词： Investments

High-Dimensional False Discovery Rate Control for Dependent Variables

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arXiv 2024年

作者： Machkour, Jasin Muma, Michael Palomar, Daniel P. The Robust Data Science Group Technische Universität Darmstadt Germany The Convex Optimization Group The Hong Kong University of Science and Technology Hong Kong

Algorithms that ensure reproducible findings from large-scale, high-dimensional data are pivotal in numerous signal processing applications. In recent years, multivariate false discovery rate (FDR) controlling methods have emerged, providing guarantees even in high-dimensional settings where the number of variables surpasses the number of samples. However, these methods often fail to reliably control the FDR in the presence of highly dependent variable groups, a common characteristic in fields such as genomics and finance. To tackle this critical issue, we introduce a novel framework that accounts for general dependency structures. Our proposed dependency-aware T-Rex selector integrates hierarchical graphical models within the T-Rex framework to effectively harness the dependency structure among variables. Leveraging martingale theory, we prove that our variable penalization mechanism ensures FDR control. We further generalize the FDR-controlling framework by stating and proving a clear condition necessary for designing both graphical and non-graphical models that capture dependencies. Additionally, we formulate a fully integrated optimal calibration algorithm that concurrently determines the parameters of the graphical model and the T-Rex framework, such that the FDR is controlled while maximizing the number of selected variables. Numerical experiments and a breast cancer survival analysis use-case demonstrate that the proposed method is the only one among the state-of-the-art benchmark methods that controls the FDR and reliably detects genes that have been previously identified to be related to breast cancer. An open-source implementation is available within the R package TRexSelector on CRAN. Copyright © 2024, The Authors. All rights reserved.

关键词： Genome

The Terminating-Random Experiments Selector: Fast High-Dimensional Variable Selection with False Discovery Rate Control

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arXiv 2021年

作者： Machkour, Jasin Muma, Michael Palomar, Daniel P. The Robust Data Science Group Technische Universität Darmstadt Germany The Convex Optimization Group Hong Kong University of Science and Technology Hong Kong

We propose the Terminating-Random Experiments (T-Rex) selector, a fast variable selection method for high-dimensional data. The T-Rex selector controls a user-defined target false discovery rate (FDR) while maximizing the number of selected variables. This is achieved by fusing the solutions of multiple early terminated random experiments. The experiments are conducted on a combination of the original predictors and multiple sets of randomly generated dummy predictors. A finite sample proof based on martingale theory for the FDR control property is provided. Numerical simulations confirm that the FDR is controlled at the target level while allowing for high power. We prove that the dummies can be sampled from any univariate probability distribution with finite expectation and variance. The computational complexity of the proposed method is linear in the number of variables. The T-Rex selector outperforms state-of-the-art methods for FDR control in numerical experiments and on a simulated genome-wide association study (GWAS), while its sequential computation time is more than two orders of magnitude lower than that of the strongest benchmark methods. The open source R package TRexSelector containing the implementation of the T-Rex selector is available on CRAN. Copyright © 2021, The Authors. All rights reserved.

关键词： Probability distributions

ON CERTAIN CONDITIONS FOR convex OPTIMIZATION IN HILBERT SPACES

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arXiv 2019年

作者： Okelo, N.B. Optimization problem Convex function Hilbert space Department of Pure and Applied Mathematics School of Mathematics and Actuarial Science Jaramogi Oginga Odinga University of Science and Technology Box 210-40601 Bondo Kenya

In this paper convex optimization techniques are employed for convex optimization problems in infinite dimensional Hilbert spaces. A first order optimality condition is given. Let f: Rn → R and let x ∈ Rn be a local solution to the problem minx∈Rn f(x). Then f′(x, d) ≥ 0 for every direction d ∈ Rn for which f′(x, d) exists. Moreover, Let f: Rn → R be differentiable at x∗ ∈ Rn. If x∗ is a local minimum of f, then ∇f(x∗) = 0. A simple application involving the Dirichlet problem is also given.46N10, 47N10 Copyright © 2019, The Authors. All rights reserved.

关键词： Hilbert spaces

Missing step detection in a high speed micro stepping motor using current feedback

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Missing step detection in a high speed micro stepping motor ...

International Conference on Control, Automation and Systems ( ICCAS)

作者： Sung-Wook Moon Young-Jin Kim Yoon-Taek Lim Dong Hwan Kim NID Graduate School Seoul National University of Science and Technology Seoul South Korea Nano Manufacturing Research Center Seoul National University of Science and Technology Seoul South Korea Convex Computer Corporation Seoul South Korea Department of Mechanical System Design Engineering Seoul National University of Science and Technology Seoul South Korea

In this work, new approach of missing step detection without using costly encoder in a micro stepping motor is proposed. For a steeping motor driver, a MOSFET driven H-bridge driver was adopted, and sinusoidal type of current is controlled to implement the micro stepping. Also, in order to investigate the missing step the current flowing the coil which is generated from the operational amplifier was given feedback and the feedback data was analyzed to detect the missing step. As a sequence, the missing step was compensated as much as the amount of the missing steps, yielding the control of the desired micro stepping angle.

关键词： Coils Torque Position control Educational institutions MOSFET circuits Power electronics