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Approximate minimum diameter
, Article 23rd International Conference on Computing and Combinatorics, COCOON 2017, 3 August 2017 through 5 August 2017 ; Volume 10392 LNCS , 2017 , Pages 237-249 ; 03029743 (ISSN); 9783319623887 (ISBN) ; Homapour, H ; Seddighin, M ; Sharif University of Technology
Springer Verlag
2017
Abstract
We study the minimum diameter problem for a set of inexact points. By inexact, we mean that the precise location of the points is not known. Instead, the location of each point is restricted to a continuous region ({Imprecise} model) or a finite set of points ({Indecisive} model). Given a set of inexact points in one of {Imprecise} or {Indecisive} models, we wish to provide a lower-bound on the diameter of the real points. In the first part of the paper, we focus on {Indecisive} model. We present an (formula presented) time approximation algorithm of factor (1+epsilon) for finding minimum diameter of a set of points in d dimensions. This improves the previously proposed algorithms for this...
Simultaneous joint and object trajectory templates for human activity recognition from 3-D data
, Article Journal of Visual Communication and Image Representation ; Volume 55 , 2018 , Pages 729-741 ; 10473203 (ISSN) ; Mohammadzade, H ; Korki, E ; Sharif University of Technology
Academic Press Inc
2018
Abstract
Availability of low-cost range sensors and the development of relatively robust algorithms for the extraction of skeleton joint locations have inspired many researchers to develop human activity recognition methods using 3-D data. In this paper, an effective method for the recognition of human activities from the normalized joint trajectories is proposed. We represent the actions as multidimensional signals and introduce a novel method for generating action templates by averaging the samples in a “dynamic time” sense. Then, in order to deal with the variations in speed and style of performing actions, we warp the samples with action templates by an efficient algorithm and employ wavelet...
Maximin share guarantee for goods with positive externalities
, Article Social Choice and Welfare ; 2020 ; Saleh, H ; Ghodsi, M ; Sharif University of Technology
Springer
2020
Abstract
One of the important yet insufficiently studied subjects in fair allocation is the externality effect among agents. For a resource allocation problem, externalities imply that the share allocated to an agent may affect the utilities of other agents. In this paper, we conduct a study of fair allocation of indivisible goods with positive externalities. Inspired by the models in the context of network diffusion, we present a simple and natural model, namely network externalities, to capture the externalities. To evaluate fairness in the network externalities model, we generalize the idea behind the notion of maximin-share (MMS) to achieve a new criterion, namely, extended-maximin-share (EMMS)....
Maximin share guarantee for goods with positive externalities
, Article Social Choice and Welfare ; Volume 56, Issue 2 , 2021 , Pages 291-324 ; 01761714 (ISSN) ; Saleh, H ; Ghodsi, M ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
One of the important yet insufficiently studied subjects in fair allocation is the externality effect among agents. For a resource allocation problem, externalities imply that the share allocated to an agent may affect the utilities of other agents. In this paper, we conduct a study of fair allocation of indivisible goods with positive externalities. Inspired by the models in the context of network diffusion, we present a simple and natural model, namely network externalities, to capture the externalities. To evaluate fairness in the network externalities model, we generalize the idea behind the notion of maximin-share (MMS) to achieve a new criterion, namely, extended-maximin-share (EMMS)....
Range-free passive acoustic localization
, Article 2008 International Conference on Intelligent Sensors, Sensor Networks and Information Processing, ISSNIP 2008, Sydney, NSW, 15 December 2008 through 18 December 2008 ; 2008 , Pages 37-42 ; 9781424429578 (ISBN) ; Abolhassani, H ; Ghodsi, M ; Sharif University of Technology
2008
Abstract
We propose a range-free localization framework in which a network of randomly deployed acoustic sensors can passively use natural acoustic phenomena within its environment to localize itself. We introduce a novel approach for registration of sensors observations which takes advantage of a clustering technique on triplets of associated observations. A Bayesian filtering method is employed to incrementally improve system state estimation as more observations become available. To the best of our knowledge this is the first work done on range-free passive acoustic localization. Simulation experiments of the proposed algorithms are presented. © 2008 IEEE
Permutation betting markets: Singleton betting with extra information
, Article Algorithmica (New York) ; Volume 60, Issue 4 , 2011 , Pages 853-876 ; 01784617 (ISSN) ; Mahini, H ; Mirrokni, V. S ; Zadimoghaddam, M ; Sharif University of Technology
2011
Abstract
We study permutation betting markets, introduced by Chen et al. (Proceedings of the ACM Conference on Electronic Commerce, 2007). For these markets, we consider subset bettings in which each trader can bet on a subset of candidates ending up in a subset of positions. We consider the revenue maximization problem for the auctioneer in two main frameworks: the risk-free revenue maximization (studied in Chen et al., Proceedings of the ACM Conference on Electronic Commerce, 2007), and the probabilistic revenue maximization. We also explore the use of some certain knowledge or extra information about the possible outcomes of the market. We first show that finding the optimal revenue in the...
Gravity on noncommutative D-branes
, Article International Journal of Modern Physics A ; Volume 18, Issue 7 , 2003 , Pages 1051-1066 ; 0217751X (ISSN) ; Arfaei, H ; Garousi, M. R ; Ghodsi, A ; Sharif University of Technology
2003
Abstract
The effective action for the low energy scattering of two gravitons with a D-brane in the presence of a constant antisymmetric B field in bosonic string theory is calculated and the modification to the standard D-brane action to first order in α′ is obtained
Almost three decades of IOI in Iran
, Article International Conference Joint with the 29th International Olympiad in Informatics, IOI 2017, 28 July 2017 through 4 August 2017 ; Volume 11, Issue Special Issue , 2017 , Pages 21-23 ; 18227732 (ISSN) ; Sharif University of Technology
Vilnius University
2017
Modeling performance of distributed programs by stochastic decision free petri nets
, Article Scientia Iranica ; Volume 8, Issue 4 , 2001 , Pages 287-296 ; 10263098 (ISSN) ; Sharif University of Technology
Sharif University of Technology
2001
Abstract
In this paper, performance modeling of synchronization delays is considered in a distributed program which consists of a number of processes that interact via message passing only. A class of timed Petri nets called Stochastic Decision Free Petri Nets (SDFPNs) is used to model such distributed programs with deterministic control flow. An exact solution technique is proposed for this model which does not follow the usual approach of reachability analysis for Petri nets and solving global balance equations for a Markovian system. Therefore, it does not require exponential distributions and does not suffer from state space explosion. The complexity of exact solution is still exponential in...
Fair allocation of indivisible goods: improvements and generalizations
, Article ACM EC 2018 - Proceedings of the 2018 ACM Conference on Economics and Computation11 June 2018 ; 11 June , 2018 , Pages 539-556 ; 9781450358293 (ISBN) ; Hajiaghayi, M ; Seddighin, M ; Seddighin, S ; Yami, H ; Sharif University of Technology
Association for Computing Machinery, Inc
2018
Abstract
We study the problem of fair allocation for indivisible goods. We use the maxmin share paradigm introduced by Budish [16] as a measure for fairness. Kurokawa, Procaccia, and Wang [36] were the first to investigate this fundamental problem in the additive setting. They show that a maxmin guarantee (1-MMS allocation) is not always possible even when the number of agents is limited to 3. While the existence of an approximation solution (e.g. a 1/2-MMS allocation) is quite straightforward, improving the guarantee becomes subtler for larger constants. Kurokawa et al. [36] provide a proof for the existence of a 2/3-MMS allocation and leave the question open for better guarantees. Our main...
Permutation betting markets: singleton betting with extra information
, Article Proceedings of the ACM Conference on Electronic Commerce, 8 July 2008 through 12 July 2008, Chicago, IL ; 2008 , Pages 180-189 ; 9781605581699 (ISBN) ; Mahini, H ; Mirrokni, V ; Zadimoghaddam, M ; ACM SIGecom ; Sharif University of Technology
2008
Abstract
We study permutation betting markets, introduced by Chen, Fortnow, Nikolova, and Pennock [3]. For these markets, we consider subset bettings in which each trader can bet on a subset of candidates ending up in a subset of positions. We consider the revenue maximization problem for the auctioneer in two main frameworks: the risk-free revenue maximization (studied in [3]), and the probabilistic revenue maximization. We also explore the use of some certain knowledge or extra information about the possible outcomes of the market. We first show that finding the optimal revenue in the risk-free model for the subset betting problem is inapproximable. This resolves an open question posed by Chen et...
Parallel online ranking of web pages
, Article IEEE International Conference on Computer Systems and Applications, 2006, Sharjah, 8 March 2006 through 8 March 2006 ; Volume 2006 , 2006 , Pages 104-109 ; 1424402123 (ISBN); 9781424402120 (ISBN) ; Sheykh Esmaili, K ; Ghodsi, M ; Abolhassani, H ; Sharif University of Technology
IEEE Computer Society
2006
Abstract
Modern search engines use link structure of the World Wide Web in order to gain better results for ranking the results of users' queries. One of the most popular ranking algorithms which is based on link analysis is HITS. It generates very accurate outputs but because of huge amount of online computations, this algorithm is relatively slow. In this paper we introduce PHITS, a parallelized version of the HITS algorithm that is suitable for working with huge web graphs in a reasonable time. For implementing this algorithm, we use WebGraph framework and we focus on parallelizing access to web graph as the main bottleneck in the HITS algorithm. © 2006 IEEE
Web graph compression by edge elimination
, Article Data Compression Conference, DCC 2006, Snowbird, UT, 28 March 2006 through 30 March 2006 ; 2006 , Pages 459- ; 10680314 (ISSN) ; Khalili, H ; Nourbakhsh, E ; Ghodsi, M ; Brandeis University ; Sharif University of Technology
2006
Fair allocation of indivisible goods: Beyond additive valuations
, Article Artificial Intelligence ; Volume 303 , 2022 ; 00043702 (ISSN) ; HajiAghayi, M ; Seddighin, M ; Seddighin, S ; Yami, H ; Sharif University of Technology
Elsevier B.V
2022
Abstract
We conduct a study on the problem of fair allocation of indivisible goods when maximin share [1] is used as the measure of fairness. Most of the current studies on this notion are limited to the case that the valuations are additive. In this paper, we go beyond additive valuations and consider the cases that the valuations are submodular, fractionally subadditive, and subadditive. We give constant approximation guarantees for agents with submodular and XOS valuations, and a logarithmic bound for the case of agents with subadditive valuations. Furthermore, we complement our results by providing close upper bounds for each class of valuation functions. Finally, we present algorithms to find...
Fair allocation of indivisible goods: Improvement
, Article Mathematics of Operations Research ; Volume 46, Issue 3 , 2021 , Pages 1038-1053 ; 0364765X (ISSN) ; Hajiaghayi, M. T ; Seddighin, M ; Seddighin, S ; Yami, H ; Sharif University of Technology
INFORMS Inst.for Operations Res.and the Management Sciences
2021
Abstract
We study the problem of fair allocation for indivisible goods. We use the maximin share paradigm introduced by Budish [Budish E (2011) The combinatorial assignment problem: Approximate competitive equilibrium from equal incomes. J. Political Econom. 119(6):1061-1103.] as a measure of fairness. Kurokawa et al. [Kurokawa D, Procaccia AD, Wang J (2018) Fair enough: Guaranteeing approximate maximin shares. J. ACM 65(2):8.] were the first to investigate this fundamental problem in the additive setting. They showed that in delicately constructed examples, not everyone can obtain a utility of at least her maximin value. They mitigated this impossibility result with a beautiful observation: no...
α-visibility
, Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) ; Volume 7357 LNCS , 2012 , Pages 1-12 ; 03029743 (ISSN) ; 9783642311543 (ISBN) ; Maheshwari, A ; Nouri, M ; Sack, J. R ; Zarrabi Zadeh, H ; Sharif University of Technology
2012
Abstract
We study a new class of visibility problems based on the notion of α-visibility. Given an angle α and a collection of line segments in the plane, a segment t is said to be α-visible from a point p, if there exists an empty triangle with one vertex at p and the side opposite to p on t such that the angle at p is α. In this model of visibility, we study the classical variants of point visibility, weak and complete segment visibility, and the construction of the visibility graph. We also investigate the natural query versions of these problems, when α is either fixed or specified at query time
Efficient Visibility Computation and Simplification in Different Environments
, Ph.D. Dissertation Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
In this thesis, we considered several types of the visibility problem. These problems include computing the visibility polygon of a point observer inside a polygonal domain, maintaining visibility polygon of a moving point observer, visibility coherence in space, maintaining visibility polygon of a moving segment observer and visibility dependent simplification. Furthermore, we considered these problems in both offline and streaming settings. These problems arise in different practical areas, such as computer graphics, machine vision, robotics, motion planning, geographic information systems (GIS) and computational geometry. We obtained effective theoretical results as well as superior...
Algorithms for Tracking Moving Points
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
Nowadays binary sensors such as infrared sensors are vastly employed in industrial, commercial and general applications due to their simplicity and low price. Beam sensors are common type of these sensors which can detect objects when they cross its beam. Sequence of sensors which are crossed in a time order is called sensor word. Consider an object, produced sensor word shows the order which it has crossed the beams. If we have more than one object then sensor word is combination of all sensor words produced by all object. We need to separate each sensor word. In this research, sensor word is developed to Fixed-Charge Minimum Cost Maximum Flow Network type.In this case, the consequent...
Diffusion of Innovations in Social Networks Based on Game Theoretic Approaches
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
Recently, computer scientists and economists have defined many joint problems and cooperate widely in various areas. Importance of this interconnection is clear for everybody, now. New works have been conducted, nowadays, to use the daily - increasing web-based social networks in viral marketing for improving companies profits. The main problem which is proved to be NP-Complete in this context is about discovering k most influential nodes in a network. In this dissertation, we generalize the problem to a group-based version and we we use group-based advertising to achieve our main goal. A new algorithm called Group-Based Diffusion technique is proposed in this thesis for solving this problem...
Profit Maximization of Sellers in Social Markets
, Ph.D. Dissertation Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
This thesis focuses on design of various strategies to maximize sellers’ profits in different social markets where agents’ behaviors and decisions are greatly influenced by their network friends. We introduce different social networks with various properties and present models to analyze the agents’ behaviors. We also study different pricing strategies for each model and design algorithms for sellers in order to maximize their profits. Furthermore, we study the prediction markets where agents with different points of views participate in the market. Each agent invests in the market with respect to her information. We propose a model for these markets which are both predictable and...