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Structured learning in time-dependent Cox models

STATISTICS IN MEDICINE 2024年第17期43卷 3164-3183页

作者： Wang, Guanbo Lian, Yi Yang, Archer Y. Platt, Robert W. Wang, Rui Perreault, Sylvie Dorais, Marc Schnitzer, Mireille E. Harvard TH Chan Sch Publ Hlth Dept Epidemiol 677 Huntington Ave Boston MA 02115 USA Univ Penn Dept Biostat Epidemiol & Informat Philadelphia PA USA McGill Univ Dept Math & Stat Montreal PQ Canada Mila Quebec AI Inst Montreal PQ Canada McGill Univ Dept Epidemiol Biostat & Occupat Hlth Montreal PQ Canada Harvard Pilgrim Hlth Care Inst Dept Populat Med Boston MA USA Harvard Med Sch Boston MA USA Harvard TH Chan Sch Publ Hlth Dept Biostat Boston MA USA Univ Montreal Fac Pharm Montreal PQ Canada StatSciences Inc Notre Dame De Lile Perrot PQ Canada Univ Montreal Dept Med Sociale & Prevent Montreal PQ Canada

Cox models with time-dependent coefficients and covariates are widely used in survival analysis. In high-dimensional settings, sparse regularization techniques are employed for variable selection, but existing methods for time-dependent Cox models lack flexibility in enforcing specific sparsity patterns (ie, covariate structures). We propose a flexible framework for variable selection in time-dependent Cox models, accommodating complex selection rules. Our method can adapt to arbitrary grouping structures, including interaction selection, temporal, spatial, tree, and directed acyclic graph structures. It achieves accurate estimation with low false alarm rates. We develop the sox package, implementing a network flow algorithm for efficiently solving models with complex covariate structures. sox offers a user-friendly interface for specifying grouping structures and delivers fast computation. Through examples, including a case study on identifying predictors of time to all-cause death in atrial fibrillation patients, we demonstrate the practical application of our method with specific selection rules.

关键词： grouping structures high-dimensional data network flow algorithm structured sparse regularization structured variable selection survival analysis time-dependent Cox models

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Pin-Accessible Legalization for Mixed-Cell-Height Circuits

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IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS 2022年第1期41卷 143-154页

作者： Li, Haocheng Chow, Wing-Kai Chen, Gengjie Yu, Bei Young, Evangeline F. Y. Chinese Univ Hong Kong Dept Comp Sci & Engn Hong Kong Peoples R China Cadence Design Syst Austin TX 78759 USA

Placement is one of the most critical stages in the physical synthesis flow. Circuits with increasing numbers of cells of multirow height have brought challenges to traditional placers on efficiency and effectiveness. Besides providing an overlap-free solution close to the global placement (GP) solution, constraints on power and ground (P/G) alignments, fence region, and routability (e.g., edge spacing and pin short/inaccessible) should be considered. In this article, we propose a legalization method for mixed-cell-height circuits by a window-based cell insertion technique and two post-processing network flow-based optimizations. Compared with the champion of the ICCAD 2017 Contest, our algorithm achieves 35% and 13% less average and maximum displacement, respectively, as well as significantly fewer routability violations. Comparing our algorithm with the state-of-the-art algorithms on this problem, there is an 8% improvement in average displacement with comparable maximum displacement. The source code of our legalization is available at https://***/cuhk-eda/ripple.

关键词： Pins Rails Metals Linear programming Timing Standards Routing Bipartite matching legalization linear programming network flow algorithm overlap removal placement

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Mitigation of Saturated Cut-Sets During Multiple Outages to Enhance Power System Security

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IEEE TRANSACTIONS ON POWER SYSTEMS 2021年第6期36卷 5734-5745页

作者： Sen Biswas, Reetam Pal, Anamitra Werho, Trevor Vittal, Vijay Arizona State Univ Sch Elect Comp & Energy Engn Tempe AZ 85287 USA

Ensuring reliable operation of large power systems subjected to multiple outages is a challenging task because of the combinatorial nature of the problem. Traditional approaches for security assessment are often limited by their scope and/or speed, resulting in missing of critical contingencies that could lead to cascading failures. This paper proposes a two-component methodology to enhance power system security. The first component combines an efficient algorithm to detect cut-set saturation (called the feasibility test (FT) algorithm) with real-time contingency analysis (RTCA) to create an integrated corrective action (iCA), whose goal is to secure the system against cut-set saturation as well as critical branch overloads. The second component only employs the results of the FT to create a relaxed corrective action (rCA) to secure the system against post-contingency cut-set saturation. The first component is more comprehensive, but the latter is computationally more efficient. The effectiveness of the two components is evaluated based upon the number of cascade triggering contingencies alleviated, and the computation time. The results obtained by analyzing different case-studies on the IEEE 118-bus and 2000-bus synthetic Texas systems indicate that the proposed two-component methodology successfully enhances the scope and speed of power system security assessment during multiple outages.

关键词： Power systems Power system security Power system reliability Real-time systems Uninterruptible power systems Power system protection Power system faults Power system security assessment power system operations multiple outages saturated cut-set graph theory network flow algorithm

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A bi-objective optimization model to decide the lines attending a bus-stop with high passenger demands

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COMPUTERS & INDUSTRIAL ENGINEERING 2023年 186卷

作者： Esquivel-Gonzalez, Guillermo Leon, Gines Sedeno-Noda, Antonio Transportes Interurbanos Tenerife SA TITSA C-Punta Anaga 1 Santa Cruz De Tenerife Spain Univ La Laguna Dept Matemat Estadist & Invest Operat Santa Cruz De Tenerife 38271 Spain

A public transportation network must change dynamically along the time due to the variation of the mobility of the population in interurban areas. This research addresses the challenge of serving newly detected zones with high passenger demand. We present a bi-objective optimization model to determine the feasibility of meeting new demands within the existing lines of the public transportation network. The two objectives considered are to minimize passenger overload on the selected lines and minimize travel time increases for these lines. Subsequently, a polynomial-time algorithm utilizing network flow techniques is introduced to solve the bi-objective problem. The algorithm is then incorporated into the decision-making system of Transportes Interurbanos de Tenerife, S.A. We also explore the company's utilization of this tool and demonstrate its current implementation in a real case scenario where a high-demand area is detected.

关键词： Biobjective combinatorial optimization Public transportation network flow algorithm

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RippleFPGA: Routability-Driven Simultaneous Packing and Placement for Modern FPGAs

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IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS 2018年第10期37卷 2022-2035页

作者： Chen, Gengjie Pui, Chak-Wa Chow, Wing-Kai Lam, Ka-Chun Kuang, Jian Young, Evangeline F. Y. Yu, Bei Chinese Univ Hong Kong Dept Comp Sci & Engn Hong Kong Hong Kong Peoples R China

As a good tradeoff between central processing unit (CPU) and application specific integrated circuit (ASIC), field-programmable gate array (FPGA) is becoming more widely used in both industry and academia. The increasing complexity and scale of modern FPGA, however, impose great challenges on the RIGA placement and packing problem. In this paper, we propose RippleFPGA to solve the packing and placement simultaneously through a set of novel techniques: 1) smooth stair-step flow;2) implicit packing similar to ASIC legalization (LG);and 3) two-level detailed placement (DP). To enable the flow, a generic, efficient, and false-alarm-free legality checking method is also proposed. Besides, due to the insufficiency of ASIC-like congestion alleviation methods, some FPGA-routing-architecture-aware optimization techniques are proposed to improve the routability. When evaluated by ISPD 2016 Contest benchmarks, RippleFPGA has 5.1% better routed wirelength and 5.5x speedup compared to all the state-of-the-art FPGA placers.

关键词： Field-programmable gate array (FPGA) legalization network flow algorithm partitioning placement

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Finding extreme supported solutions of biobjective network flow problems: An enhanced parametric programming approach

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COMPUTERS & OPERATIONS RESEARCH 2017年 82卷 153-166页

作者： Raith, Andrea Sedeno-Noda, Antonio Univ Auckland Dept Engn Sci Private Bag 92019 Auckland New Zealand Univ La Laguna Dept Matemat Estadist & Invest Operat San Cristobal De La Lagu 38271 Santa Cruz De T Spain

We address the problem of determining a complete set of extreme supported efficient solutions of biobjective minimum cost flow (BMCF) problems. A novel method improving the classical parametric method for this biobjective problem is proposed. The algorithm runs in O(Nn(m + nlogn)) time determining all extreme supported non-dominated points in the outcome space and one extreme supported efficient solution associated with each one of them. Here n is the number of nodes, m is the number of arcs and N is the number of extreme supported non-dominated points in outcome space for the BMCF problem. The memory space required by the algorithm is O(n + m) when the extreme supported efficient solutions are not required to be stored in RAM. Otherwise, the algorithm requires O(N + m) space. Extensive computational experiments comparing the performance of the proposed method and a standard parametric network simplex method are presented. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Biobjective minimum cost flow problem Extreme supported efficient solutions network flow algorithm Parametric simplex method

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Evacuation Planning with Endogenous Transportation network Degradations: A Stochastic Cell-Based Model and Solution Procedure

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networkS & SPATIAL ECONOMICS 2015年第3期15卷 677-696页

作者： Li, Jian Ozbay, Kaan Hong Kong Polytech Univ Dept Civil & Environm Engn Kowloon Hong Kong Peoples R China NYU CUSP Dept Civil & Urban Engn Brooklyn NY 11201 USA

Capturing the impact of uncertain events in emergency evacuation time estimation is an important issue for public officials to avoid unexpected delays and related losses of life and property. However, most of the current studies in evacuation planning only focus on exogenous uncertainties, such as flooding damage in a hurricane, but ignore uncertainties caused by endogenously determined risks, or so called flow-related risks. This paper proposes an analytical framework along with an efficient solution methodology to evaluate the impact of endogenously determined risks in order to estimate evacuation time. We incorporate the probability function of endogenously determined risks in a cell-based macroscopic evacuation model. A network flow algorithm based on the sample average approximation approach is used as part of the solution procedure. Finally, a sample network is used to demonstrate the salient features of the proposed stochastic model and solution procedure.

关键词： Evacuation planning Endogenously determined risks network flow algorithm

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SlackProbe: A Flexible and Efficient In Situ Timing Slack Monitoring Methodology

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IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS 2014年第8期33卷 1168-1179页

作者： Lai, Liangzhen Chandra, Vikas Aitken, Robert C. Gupta, Puneet Univ Calif Los Angeles Dept Elect Engn Los Angeles CA 90095 USA ARM Inc San Jose CA 95134 USA

In situ monitoring is an accurate way to monitor circuit delay or timing slack, but usually incurs significant overhead. We observe that most existing slack monitoring methods focus exclusively on monitoring path endpoints, which is not cost efficient from power and area perspectives. In this paper, we first propose SlackProbe methodology, which inserts timing slack monitors like probes at a selected set of nets, including intermediate nets along critical paths. SlackProbe can be used to detect impending delay failures due to various reasons (process variations, ambient fluctuations, circuit aging, etc.) and can be used with various preventive actions (e. g., voltage/frequency scaling, clock stretching/time borrowing, etc.). Then we perform thorough analysis of the potential benefits and caveats of SlackProbe over conventional approaches in terms of number of monitors required, monitoring efficiency and observability, delay margin, and design perturbation. Experimental results on commercial processors show that with 5% extra timing margin, SlackProbe can reduce the number of monitors by 12-16X as compared to the number of monitors inserted at path ending pins. SlackProbe can also improve the monitoring efficiency by up to 1.9X and improve the monitoring observability by up to 32%, as compared to endpoint monitoring.

关键词： Average case design delay testing low-power design network flow algorithm timing

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BONNPLACE Legalization: Minimizing Movement by Iterative Augmentation

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IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS 2013年第8期32卷 1215-1227页

作者： Brenner, Ulrich Univ Bonn Res Inst Discrete Math D-53012 Bonn Germany

We describe BONNPLACELEGAL, an algorithm for VLSI placement legalization. Based on a minimum-cost flow algorithm that iteratively augments flows along paths, our approach ensures that only augmentations are considered that can be realized exactly by cell movements. Hence, this method avoids realization problems that are inherent to previous flow-based legalization algorithms. As a result, it combines the global perspective of minimum-cost flow approaches with the efficiency of local search algorithms. The tool is mainly designed to minimize total and maximum cell movement, but it is flexible enough to optimize other objective functions provided that the effect of single cell movements on them can be estimated efficiently. We compare our approach to legalization tools from industry and academia by experiments on dense recent real-world designs and public benchmarks. The results show that we are much faster and produce significantly better results in terms of average (linear and quadratic) and maximum movement than any other tool. The experiments also demonstrate that by minimizing squared movement we also produce a smaller increase in net length than the other tools.

关键词： Legalization network flow algorithm overlap removal physical design placement

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A network approach to modeling the multi-echelon spare-part inventory system with backorders and interval-valued demand

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INTERNATIONAL JOURNAL OF PRODUCTION ECONOMICS 2011年第1期132卷 43-51页

作者： Levner, Eugene Perlman, Yael Cheng, T. C. E. Levner, Ilya Bar Ilan Univ Dept Management IL-52900 Ramat Gan Israel Ashkelon Acad Coll Sch Econ Ashqelon Israel Hong Kong Polytech Univ Dept Logist & Maritime Studies Kowloon Hong Kong Peoples R China

A multi-echelon inventory system implies the existence of a hierarchy of stocking locations, and the dependence and interaction between them. We consider a multi-echelon, spare-part inventory management problem with outsourcing and backordering. The problem is characterized by deterministic repair time/cost, and supply and demand that lie within prescribed intervals and that vary over time. The objective is to minimize the total inventory and transportation costs. We develop a network model for problem analysis and present a network flow algorithm for solving the problem. We prove that the Wagner-Whitin property, known for the lot-sizing problem, can be extended to the spare-part inventory management problem under study. (C) 2011 Elsevier B.V. All rights reserved.

关键词： Spare-part inventory management Multi-suppliers Backorders network model network flow algorithm Wagner-Whitin property

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