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arXiv 2019年

作者： Mokhtari, Aryan Ozdaglar, Asuman Pattathil, Sarath Laboratory for Information and Decision Systems Massachusetts Institute of Technology CambridgeMA United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA United States

In this paper we consider solving saddle point problems using two variants of Gradient Descent- Ascent algorithms, Extra-gradient (EG) and Optimistic Gradient Descent Ascent (OGDA) methods. We show that both of these algorithms admit a unified analysis as approximations of the classical proximal point method for solving saddle point problems. This viewpoint enables us to develop a new framework for analyzing EG and OGDA for bilinear and strongly convex- strongly concave settings. Moreover, we use the proximal point approximation interpretation to generalize the results for OGDA for a wide range of parameters. Copyright © 2019, The Authors. All rights reserved.

关键词： Gradient methods

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Convergence rate of O(1/k) for optimistic gradient and extra-gradient methods in smooth convex-concave saddle point problems

arXiv

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arXiv 2019年

We study the iteration complexity of the optimistic gradient descent-ascent (OGDA) method and the extra-gradient (EG) method for finding a saddle point of a convex-convex uncon- strained min-max problem. To do so, we first show that both OGDA and EG can be interpreted as approximate variants of the proximal point method. We then exploit this interpretation to show that both algorithms produce iterates that remain within a bounded set. We further show that the function value of the averaged iterates generated by both of these algorithms converge with a rate of O(1/k) to the function value at the saddle point. Our theoretical analysis is of interest as it provides a simple convergence analysis for the EG algorithm in terms of function value without using compactness assumption. Moreover, it provides the first convergence rate estimate for OGDA in the general convex-concave setting. Copyright © 2019, The Authors. All rights reserved.

关键词： Gradient methods

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Competitive contagion with sparse seeding

arXiv

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arXiv 2019年

作者： Siami, Milad Ajorlou, Amir Jadbabaie, Ali Institute for Data Systems and Society Massachusetts Institute of Technology CambridgeMA02139 United States Electrical and Computer Engineering Department Northeastern University BostonMA02115 United States

This paper studies a strategic model of marketing and product diffusion in social networks. We consider two firms offering substitutable products which can improve their market share by seeding the key individuals in the market. Consumers update their consumption level for each of the two products as the best response to the consumption of their neighbors in the previous period. This results in linear update dynamics for the product consumption. Each consumer receives externality from the consumption of each neighbor where the strength of the externality is higher for consumption of the products of the same firm. We represent the above setting as a duopoly game between the firms and introduce a novel framework that allows for sparse seeding to emerge as an equilibrium strategy. We then study the effect of the network structure on the optimal seeding strategies and the extent to which the strategies can be sparsified. In particular, we derive conditions under which near Nash equilibrium strategies can asymptotically lead to sparse seeding in large populations. The results are illustrated using a coreperiphery network. Copyright © 2019, The Authors. All rights reserved.

关键词： Game theory

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From Population Games to Payoff Dynamics Models: A Passivity-Based Approac

From Population Games to Payoff Dynamics Models: A Passivity...

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IEEE Annual Conference on Decision and Control

作者： Shinkyu Park Nuno C. Martins Jeff S. Shamma Department of Mechanical and Aerospace Engineering Princeton University Princeton NJ USA Department of Electrical and Computer Engineering and the Institute for Systems Research University of Maryland College Park MD USA Computer Electrical and Mathematical Science and Engineering Division (CEMSE) King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia

ISBN: (数字)9781728113982

ISBN: (纸本)9781728113999

This tutorial article describes a dynamical systems framework rooted in evolutionary game principles to characterize non-cooperative strategic interactions among large populations of bounded rationality agents. It also overviews recent results that use passivity notions to characterize the stability of Nash-like equilibria. In our framework, each agent belongs to a population that prescribes to its members a strategy set and a strategy revision protocol. A so-called social state registers the proportions of agents in every population adopting each strategy and a pre-selected dynamic payoff mechanism, specified by a payoff dynamics model (PDM), determines the payoff as a causal map of the social state. According to the framework, each agent must take up a strategy at a time, which it can repeatedly revise over time based on its current strategy, and information about the payoff and social state available to it. The PDM class considered in our framework can model precisely or approximately prevalent dynamic behaviors such as inertia and delays that are inherent to learning and network effects, which cannot be captured using conventional memoryless payoff mechanisms (often referred to as population games).We organize the article in two main parts. The first introduces basic concepts prevailing in existing approaches in which a population game determines the payoff, while the second considers rather general PDM classes, of which every population game is a particular case. The latter expounds a passivity-based methodology to characterize convergence of the social state to Nash-like equilibria.

关键词： Sociology Statistics Games Stability analysis Tutorials Protocols Delays

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Wildfire Monitoring in Remote Areas using Autonomous Unmanned Aerial Vehicles

Wildfire Monitoring in Remote Areas using Autonomous Unmanne...

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IEEE Conference on computer Communications Workshops, INFOCOM Wksps

作者： Fatemeh Afghah Abolfazl Razi Jacob Chakareski Jonathan Ashdown School of Informatics Computing and Cyber Systems Northern Arizona University Flagstaff AZ USA Electrical and Computer Engineering University of Alabama Tuscaloosa AL USA Computer Information Systems Department SUNY Polytechnic Institute Utica NY USA

In this paper, we propose a drone-based wildfire monitoring system for remote and hard-to-reach areas. This system utilizes autonomous unmanned aerial vehicles (UAVs) with the main advantage of providing on-demand monitoring service faster than the current approaches of using satellite images, manned aircraft and remotely controlled drones. Furthermore, using autonomous drones facilitates minimizing human intervention in risky wildfire zones. In particular, to develop a fully autonomous system, we propose a distributed leader-follower coalition formation model to cluster a set of drones into multiple coalitions that collectively cover the designated monitoring field. The coalition leader is a drone that employs observer drones potentially with different sensing and imaging capabilities to hover in circular paths and collect imagery information from the impacted areas. The objectives of the proposed system include: i) to cover the entire fire zone with a minimum number of drones, and ii) to minimize the energy consumption and latency of the available drones to fly to the fire zone. Simulation results confirm that the performance of the proposed system- without the need for inter-coalition communications- approaches that of a centrally-optimized system.

关键词： Drones Monitoring Robot sensing systems Task analysis Observers Forestry

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Effective Computation of All Stabilizing Gain and Delay Regions for MIMO systems 14

Effective Computation of All Stabilizing Gain and Delay Regi...

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14th IEEE International Conference on Control and Automation, ICCA 2018

作者： Qing-Guo, Wang Nguyen, Le Binh Institute for Intelligent Systems Faculty of Engineering and the Built Environment University of Johannesburg South Africa Department of Electrical and Computer Engineering National University of Singapore Singapore Singapore

ISBN: (纸本)9781538660898

This paper deals with determining all the loop gain and delay regions for closed-loop stability of a multivariable system. Such a problem admits no analytical solutions in general. Instead, we graphically determine stability boundaries in the gain-delay space based on the condition of the intersection of the characteristic loci with the critical point and decide stability of the regions divided by these boundaries with helps of a new perturbation analysis of parameters on change of closed-loop poles. This procedure yields all the stable regions, each of which captures the full information on the stabilizing loop gain interval versus any loop delay. The regions then also contain, as by- product, the information on gain and delay margins for stability. The stabilizing set is useful for stability robustness analysis, robust control design and system optimization. Several examples are provided to illustrate the effectiveness of the method. © 2018 IEEE.

关键词： MIMO systems

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Perceived Stiffness Estimation for Robot Force Control

Perceived Stiffness Estimation for Robot Force Control

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IEEE International Conference on robotics and Automation

作者： Luis Santos Rui Cortesao Institute of Systems and Robotics University of Coimbra Portugal Electrical and Computer Engineering Department University of Coimbra Portugal

Typical robot force control architectures have a positive force feedback loop to decouple robot dynamics from contact dynamics. Due to the noisy profile of force measurements, it is common to filter force signals by low pass filters. This paper shows that, when force feedback is filtered, robot and environment dynamics are no longer decoupled, affecting force control performance. Additionally, the perceived stiffness from the force control perspective, is correlated with the robot effective mass. To cope with this issue, a force based stiffness estimation strategy that also includes the inertial properties (effective mass) in the estimation algorithm is proposed, allowing to adapt control gains based on the robot effective mass. In this way, the perceived stiffness can be seen as a control optimization parameter, rather than a well defined physical property. Simulation and experimental results with a 1-DoF robot and 7-DoF manipulator, respectively, validate the estimation strategy, showing better force control results with the perceived stiffness in the control loop, as compared to the real environment stiffness.

关键词： Robots Force Estimation Dynamics Force control Effective mass Adaptation models

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Enhanced algorithmic implementation to assist real-time indoor map generation for vision impaired individuals 13

Enhanced algorithmic implementation to assist real-time indo...

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13th International Conference on computer Science and Education, ICCSE 2018

作者： Jayakody, J.A.D.C. Murray, I. Hermann, J. Lokuliyana, S. Dunuwila, V.R. Curtin University of Technology Department of Electrical and Computer Engineering BentleyWA Australia Sri Lanka Institute of Information Technology Department of Information Systems Engineering Malabe Sri Lanka

ISBN: (纸本)9781538654958

The complexity of indoor environments has made navigation difficult for vision impaired individuals as well as individuals with clear vision. Although handheld mobility devices have been developed to assist the vision impaired in navigation, they are incapable of capturing parameters such as distance, angle and direction. This paper presents an appraised framework;the Accessible Building Information Model (AccessBIM), which could be used for generating an indoor map in real-time with the classification of real world objects and their locations. The AccessBIM database is equipped with two optimization algorithms;a database optimization algorithm that reduces the time of query execution through indexing, query re-writing, schema redesigning and a memory optimization algorithm known as 'Memcache'. Five scenarios were tested using a simulator to determine the accuracy of the map that is generated. The use of the two algorithms ensured that the real-time map generated through the data collected from the simulation environment was similar to the actual floor plan. Hence, it can be concluded that the AccessBIM framework has the potential to play an integral role in assistive technologies related to localization and mapping, thus significantly improving the quality of life for individuals with vision impairment. © 2018 IEEE.

关键词： Navigation

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Tempcache: A database optimization algorithm for real-time data handling in indoor spatial environments 13

Tempcache: A database optimization algorithm for real-time d...

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13th International Conference on computer Science and Education, ICCSE 2018

ISBN: (纸本)9781538654958

The unstable arrangement of modern indoor environments has made navigation within buildings a difficult task. Hence, this paper introduces the AccessBIM framework, which is an efficient real-time indoor navigation system that facilitates in generating a real-time indoor map by crowdsourcing spatial data through the sensors available in mobile devices of navigators. The framework is equipped with a database optimization algorithm known as 'Tempcache' which reduces the time and cost of searching data by examining the AccessBIM database for previously navigated paths, thus enabling faster data retrieval through efficient query processing. A simulation of a virtual environment similar to an actual indoor environment was used to test the algorithm. The significance of the algorithm was validated by comparing the total map generation time before and after the algorithm was applied for which the results demonstrated a reduction in map generation time with the use of the algorithm. The framework is also capable of capturing localization information with the support of i-Beacons which is then stored in a cloud server. © 2018 IEEE.

关键词： Crowdsourcing

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Beryllium polyhydride Be4H8(H2)2 synthesized at high pressure and temperature

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Physical Review Materials 2020年第12期4卷 125402-125402页

作者： Takahiro Matsuoka Hiroshi Fujihisa Takahiro Ishikawa Takaya Nakagawa Keiji Kuno Naohisa Hirao Yasuo Ohishi Katsuya Shimizu Shigeo Sasaki Department of Electrical Electronic and Computer Engineering Faculty of Engineering Gifu University Gifu 501-1193 Japan Material Science and Engineering Joint Institute for Advanced Materials (JIAM) The University of Tennessee Knoxville Tennessee 37996 USA National Institute of Advanced Industrial Science and Technology (AIST) Ibaraki 305-8565 Japan The Elements Strategy Initiative Center for Magnetic Materials National Institute for Materials Science Ibaraki 305-0047 Japan Materials Science and Technology Division Graduate School of Engineering Gifu University Gifu 501-1193 Japan Environmental and Renewable Energy Systems Division Gifu University Gifu 501-1193 Japan Japan Synchrotron Radiation Research Institute (JASRI) Hyogo 679-5198 Japan Center for Science and Technology under Extreme Conditions Graduate School of Engineering Science Osaka University Osaka 560-8531 Japan

We report x-ray diffraction and Raman scattering measurements in combination with density functional theory calculations that reveal the formation of beryllium polyhydride Be4H8(H2)2 by the laser heating of a Be-H2 mixture to above 1700 K at pressures between 5 and 8 GPa. Be4H8(H2)2 crystallizes in a P63/mmc structure and consists of the corner-sharing BeH4 tetrahedrons and the H2 molecules that occupy an interstitial site. Be4H8(H2)2 is stable at least to 14 GPa upon compression and stable down to 4 GPa at room temperature. Our ab initio calculations suggest that Be4H8(H2)2 is a metastable phase of the Be-H system.

关键词： Composition Pressure effects Structural properties Hydrides Ab initio calculations Density functional theory Raman spectroscopy X-ray diffraction

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