The Experts below are selected from a list of 155079 Experts worldwide ranked by ideXlab platform
Sergey Yekhanin - One of the best experts on this subject based on the ideXlab platform.
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a Geometric Approach to information theoretic private information retrieval
SIAM Journal on Computing, 2007Co-Authors: David P Woodruff, Sergey YekhaninAbstract:A $t$-private private information retrieval (PIR) scheme allows a user to retrieve the $i$th bit of an $n$-bit string $x$ replicated among $k$ servers, while any coalition of up to $t$ servers learns no information about $i$. We present a new Geometric Approach to PIR and obtain the following: (1) A $t$-private $k$-server protocol with communication $O (\frac{k^2}{t} \log k n^{1/\left \lfloor (2k-1)/t \right \rfloor})$, removing the ${k}{t}$ term of previous schemes. This answers an open question of [Y. Ishai and E. Kushilevitz, in Proceedings of the $31$st ACM Symposium on Theory of Computing, 1999, pp. 79-88]. (2) A $2$-server protocol with $O(n^{1/3})$ communication, polynomial preprocessing, and online work $O(n/\log^r n)$ for any constant $r$. This improves the $O(n/\log^2 n)$ work of [A. Beimel, Y. Ishai, and T. Malkin, J. Cryptology, 17 (2004), pp. 125-151]. (3) Smaller communication for instance hiding [D. Beaver, J. Feigenbaum, J. Kilian, and P. Rogaway, J. Cryptology, 10 (1997), pp. 17-36; Y. Ishai and E. Kushilevitz, in Proceedings of the $31$st ACM Symposium on Theory of Computing, 1999, pp. 79-88], PIR with a polylogarithmic number of servers, and robust PIR [A. Beimel and Y. Stahl, in Proceedings of the $3$rd Conference on Security in Communications Networks (SCN $2002$), Lecture Notes in Comput. Sci. 2576, Springer, Berlin, 2003, pp. 326-341].
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a Geometric Approach to information theoretic private information retrieval
Conference on Computational Complexity, 2005Co-Authors: David P Woodruff, Sergey YekhaninAbstract:A t-private private information retrieval (PIR) scheme allows a user to retrieve the ith bit of an n-bit string x replicated among k servers, while any coalition of up to t servers learns no information about i. We present a new Geometric Approach to PIR, and obtain: 1) a t-private k-server protocol with communication O((k/sup 2//t) log k n/sup 1//spl lfloor//(2k - 1)/spl rfloor/) removing the (t) term of previous schemes. This answers an open question of Ishai and Kushilevitz (1999). 2) A 2-server protocol with O(n/sup 1/3/) communication, polynomial preprocessing, and online work O(n/log/sup r/ n) for any constant r. This improves the O(n/log/sup 2/ n) work of Beimel et al. (2000). 3) Smaller communication for instance hiding, PIR with a polylogarithmic number of servers, robust PIR, and PIR with fixed answer sizes. To illustrate the power of our Approach, we also give alternative, Geometric proofs of some of the best 1-private upper bounds.
Frederick A Matsen - One of the best experts on this subject based on the ideXlab platform.
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a Geometric Approach to tree shape statistics
Systematic Biology, 2006Co-Authors: Frederick A MatsenAbstract:This article presents a new way to quantify the descriptive ability of tree shape statistics. Where before, tree shape statistics were chosen by their ability to distinguish between macroevolutionary models, the resolution presented in this paper quantifies the ability of a statistic to differentiate between similar and different trees. This is termed the Geometric Approach to differentiate it from the model-based Approach previously explored. A distinct advantage of this perspective is that it allows evaluation of multiple tree shape statistics describing different aspects of tree shape. After developing the methodology, it is applied here to make specific recommendations for a suite of three statistics that may prove useful in applications. The article ends with an application of the statistics to clarify the impact of taxa omission on tree shape.
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a Geometric Approach to tree shape statistics
arXiv: Populations and Evolution, 2005Co-Authors: Frederick A MatsenAbstract:This article presents a new way to understand the descriptive ability of tree shape statistics. Where before tree shape statistics were chosen by their ability to distinguish between macroevolutionary models, the ``resolution'' presented in this paper quantifies the ability of a statistic to differentiate between similar and different trees. We term this a ``Geometric'' Approach to differentiate it from the model-based Approach previously explored. A distinct advantage of this perspective is that it allows evaluation of multiple tree shape statistics describing different aspects of tree shape. After developing the methodology, it is applied here to make specific recommendations for a suite of three statistics which will hopefully prove useful in applications. The article ends with an application of the tree shape statistics to clarify the impact of omission of taxa on tree shape.
David P Woodruff - One of the best experts on this subject based on the ideXlab platform.
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a Geometric Approach to information theoretic private information retrieval
SIAM Journal on Computing, 2007Co-Authors: David P Woodruff, Sergey YekhaninAbstract:A $t$-private private information retrieval (PIR) scheme allows a user to retrieve the $i$th bit of an $n$-bit string $x$ replicated among $k$ servers, while any coalition of up to $t$ servers learns no information about $i$. We present a new Geometric Approach to PIR and obtain the following: (1) A $t$-private $k$-server protocol with communication $O (\frac{k^2}{t} \log k n^{1/\left \lfloor (2k-1)/t \right \rfloor})$, removing the ${k}{t}$ term of previous schemes. This answers an open question of [Y. Ishai and E. Kushilevitz, in Proceedings of the $31$st ACM Symposium on Theory of Computing, 1999, pp. 79-88]. (2) A $2$-server protocol with $O(n^{1/3})$ communication, polynomial preprocessing, and online work $O(n/\log^r n)$ for any constant $r$. This improves the $O(n/\log^2 n)$ work of [A. Beimel, Y. Ishai, and T. Malkin, J. Cryptology, 17 (2004), pp. 125-151]. (3) Smaller communication for instance hiding [D. Beaver, J. Feigenbaum, J. Kilian, and P. Rogaway, J. Cryptology, 10 (1997), pp. 17-36; Y. Ishai and E. Kushilevitz, in Proceedings of the $31$st ACM Symposium on Theory of Computing, 1999, pp. 79-88], PIR with a polylogarithmic number of servers, and robust PIR [A. Beimel and Y. Stahl, in Proceedings of the $3$rd Conference on Security in Communications Networks (SCN $2002$), Lecture Notes in Comput. Sci. 2576, Springer, Berlin, 2003, pp. 326-341].
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a Geometric Approach to information theoretic private information retrieval
Conference on Computational Complexity, 2005Co-Authors: David P Woodruff, Sergey YekhaninAbstract:A t-private private information retrieval (PIR) scheme allows a user to retrieve the ith bit of an n-bit string x replicated among k servers, while any coalition of up to t servers learns no information about i. We present a new Geometric Approach to PIR, and obtain: 1) a t-private k-server protocol with communication O((k/sup 2//t) log k n/sup 1//spl lfloor//(2k - 1)/spl rfloor/) removing the (t) term of previous schemes. This answers an open question of Ishai and Kushilevitz (1999). 2) A 2-server protocol with O(n/sup 1/3/) communication, polynomial preprocessing, and online work O(n/log/sup r/ n) for any constant r. This improves the O(n/log/sup 2/ n) work of Beimel et al. (2000). 3) Smaller communication for instance hiding, PIR with a polylogarithmic number of servers, robust PIR, and PIR with fixed answer sizes. To illustrate the power of our Approach, we also give alternative, Geometric proofs of some of the best 1-private upper bounds.
Torra Porras Salvador - One of the best experts on this subject based on the ideXlab platform.
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A Geometric Approach to proxy economic uncertainty by a metric of disagreement among qualitative expectations
Universitat de Barcelona. Facultat d'Economia i Empresa, 2018Co-Authors: Clavería González Óscar, Monte Moreno Enric, Torra Porras SalvadorAbstract:In this study we present a Geometric Approach to proxy economic uncertainty. We design a positional indicator of disagreement among survey-based agents' expectations about the state of the economy. Previous dispersion-based uncertainty indicators derived from business and consumer surveys exclusively make use of the two extreme pieces of information coming from the respondents expecting a variable to rise and to fall. With the aim of also incorporating the information coming from the share of respondents expecting a variable to remain constant, we propose a Geometrical framework and use a barycentric coordinate system to generate a measure of disagreement, referred to as a discrepancy indicator. ..
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A Geometric Approach to proxy economic uncertainty by a metric of disagreement among qualitative expectations
2018Co-Authors: Clavería González Óscar, Monte Moreno Enrique, Torra Porras SalvadorAbstract:Working paperIn this study we present a Geometric Approach to proxy economic uncertainty. We design a positional indicator of disagreement among survey-based agents' expectations about the state of the economy. Previous dispersion-based uncertainty indicators derived from business and consumer surveys exclusively make use of the two extreme pieces of information coming from the respondents expecting a variable to rise and to fall. With the aim of also incorporating the information coming from the share of respondents expecting a variable to remain constant, we propose a Geometrical framework and use a barycentric coordinate system to generate a measure of disagreement, referred to as a discrepancy indicator. We assess its performance, both empirically and experimentally, by comparing it to the standard deviation of the share of positive and negative responses, which has been used by Bachman et al. (2013) as a proxy for economic uncertainty. When applied in sixteen European countries, we find that both time-varying metrics co-evolve in most countries for expectations about the country's overall economic situation in the present, but not in the future. Additionally, we obtain their simulated sampling distributions and we find that the proposed indicator gravitates uniformly towards the three vertices of the simplex representing the three answering categories, as opposed to the standard deviation, which tends to overestimate the level of uncertainty as a result of ignoring the no-change responses. Consequently, we find evidence that the information coming from agents expecting a variable to remain constant has an effect on the measurement of disagreement.Preprin
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A Geometric Approach to proxy economic uncertainty by a metric of disagreement among qualitative expectations
2018Co-Authors: Clavería González Óscar, Monte Moreno Enrique, Torra Porras SalvadorAbstract:Working paperIn this study we present a Geometric Approach to proxy economic uncertainty. We design a positional indicator of disagreement among survey-based agents' expectations about the state of the economy. Previous dispersion-based uncertainty indicators derived from business and consumer surveys exclusively make use of the two extreme pieces of information coming from the respondents expecting a variable to rise and to fall. With the aim of also incorporating the information coming from the share of respondents expecting a variable to remain constant, we propose a Geometrical framework and use a barycentric coordinate system to generate a measure of disagreement, referred to as a discrepancy indicator. We assess its performance, both empirically and experimentally, by comparing it to the standard deviation of the share of positive and negative responses, which has been used by Bachman et al. (2013) as a proxy for economic uncertainty. When applied in sixteen European countries, we find that both time-varying metrics co-evolve in most countries for expectations about the country's overall economic situation in the present, but not in the future. Additionally, we obtain their simulated sampling distributions and we find that the proposed indicator gravitates uniformly towards the three vertices of the simplex representing the three answering categories, as opposed to the standard deviation, which tends to overestimate the level of uncertainty as a result of ignoring the no-change responses. Consequently, we find evidence that the information coming from agents expecting a variable to remain constant has an effect on the measurement of disagreement
Karanjit Kalsi - One of the best experts on this subject based on the ideXlab platform.
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approximating flexibility in distributed energy resources a Geometric Approach
Power Systems Computation Conference, 2018Co-Authors: Soumya Kundu, Karanjit Kalsi, Scott BackhausAbstract:With increasing availability of communication and control infrastructure at the distribution systems, it is expected that the distributed energy resources (DERs) will take an active part in future power systems operations. One of the main challenges associated with integration of DERs in grid planning and control is in estimating the available flexibility in a collection of (heterogeneous) DERs, each of which may have local constraints that vary over time. In this work, we present a Geometric Approach for approximating the flexibility of a DER in modulating its active and reactive power consumption. The proposed method is agnostic about the type and model of the DERs, thereby facilitating a plug-and-play Approach, and allows scalable aggregation of the flexibility of a collection of (heterogeneous) DERs at the distributed system level. Simulation results are presented to demonstrate the performance of the proposed method.
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a Geometric Approach to aggregate flexibility modeling of thermostatically controlled loads
IEEE Transactions on Power Systems, 2017Co-Authors: Lin Zhao, Wei Zhang, He Hao, Karanjit KalsiAbstract:Coordinated aggregation of a large population of thermostatically controlled loads (TCLs) presents a great potential to provide various ancillary services to the grid. One of the key challenges of integrating TCLs into system-level operation and control is developing a simple and portable model to accurately capture their aggregate flexibility. In this paper, we propose a Geometric Approach to model the aggregate flexibility of TCLs. We show that the set of admissible power profiles of an individual TCL is a polytope, and their aggregate flexibility is the Minkowski sum of the individual polytopes. In order to represent their aggregate flexibility in an intuitive way and achieve a tractable approximation, we develop optimization-based algorithms to approximate the polytopes by the homothets of a given convex set. As a special application, this set is chosen as a virtual battery model, and the corresponding optimal approximations are solved efficiently by equivalent linear programming problems. Numerical results show that our algorithms yield significant improvement in characterizing the aggregate flexibility over existing modeling methods. We also conduct case studies to demonstrate the efficacy of our Approaches by coordinating TCLs to track a frequency regulation signal from the Pennsylvania-New Jersey-Maryland Interconnection.
