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Generalized Stochastic Matching [article]

Alireza Farhadi, Jacob Gilbert, MohammadTaghi Hajiaghayi
2022 arXiv   pre-print
.; Farhadi, A.; Hajiaghayi, M.; and Reyhani, N. 2019a. Stochastic Matching on Uni- formly Sparse Graphs.  ...  Behnezhad, S.; Farhadi, A.; Hajiaghayi, M.; and Reyhani, N. 2019b. Stochastic Matching with Few Queries: New Al- gorithms and Tools. In Chan, T.  ... 
arXiv:2205.14717v1 fatcat:rnyceccsezeonjljtuknadcc4q

Online Bipartite Matching with Reusable Resources [article]

Steven Delong, Alireza Farhadi, Rad Niazadeh, Balasubramanian Sivan
2021 arXiv   pre-print
We study the classic online bipartite matching problem with a twist: offline nodes are reusable any number of times. Every offline node i becomes available d steps after it was assigned to. Nothing better than a 0.5-approximation, obtained by the trivial deterministic greedy algorithm, was known for this problem. We give the first approximation factor beating 0.5, namely a 0.505 approximation, by suitably adapting and interpreting the powerful technique of Online Correlated Selection.
arXiv:2110.07084v1 fatcat:3g45vtfel5fgxnk4pig7tasatq

Approximate Maximum Matching in Random Streams [article]

Alireza Farhadi, MohammadTaghi Hajiaghayi, Tung Mai, Anup Rao, Ryan A. Rossi
2019 arXiv   pre-print
In this paper, we study the problem of finding a maximum matching in the semi-streaming model when edges arrive in a random order. In the semi-streaming model, an algorithm receives a stream of edges and it is allowed to have a memory of Õ(n) where n is the number of vertices in the graph. A recent inspiring work by Assadi et al. shows that there exists a streaming algorithm with the approximation ratio of 2/3 that uses Õ(n^1.5) memory. However, the memory of their algorithm is much larger than
more » ... the memory constraint of the semi-streaming algorithms. In this work, we further investigate this problem in the semi-streaming model, and we present simple algorithms for approximating maximum matching in the semi-streaming model. Our main results are as follows. We show that there exists a single-pass deterministic semi-streaming algorithm that finds a 3/5 (= 0.6) approximation of the maximum matching in bipartite graphs using Õ(n) memory. This result significantly outperforms the state-of-the-art result of Konrad that finds a 0.539 approximation of the maximum matching using Õ(n) memory. By giving a black-box reduction from finding a matching in general graphs to finding a matching in bipartite graphs, we show there exists a single-pass deterministic semi-streaming algorithm that finds a 6/11 (≈ 0.545) approximation of the maximum matching in general graphs, improving upon the state-of-art result 0.506 approximation by Gamlath et al.
arXiv:1912.10497v1 fatcat:gzp57m3a2fb3ficgobweuz5opa

On the Complexity of Chore Division [article]

Alireza Farhadi, MohammadTaghi Hajiaghayi
2018 arXiv   pre-print
We study the proportional chore division problem where a protocol wants to divide an undesirable object, called chore, among n different players. The goal is to find an allocation such that the cost of the chore assigned to each player be at most 1/n of the total cost. This problem is the dual variant of the cake cutting problem in which we want to allocate a desirable object. Edmonds and Pruhs showed that any protocol for the proportional cake cutting must use at least Ω(n n) queries in the
more » ... st case, however, finding a lower bound for the proportional chore division remained an interesting open problem. We show that chore division and cake cutting problems are closely related to each other and provide an Ω(n n) lower bound for chore division.
arXiv:1710.00271v2 fatcat:nynumy22vvgvnc4ksd3l7wybdy

Understanding egocentric activities

Alireza Fathi, Ali Farhadi, James M. Rehg
2011 2011 International Conference on Computer Vision  
We present a method to analyze daily activities, such as meal preparation, using video from an egocentric camera. Our method performs inference about activities, actions, hands, and objects. Daily activities are a challenging domain for activity recognition which are well-suited to an egocentric approach. In contrast to previous activity recognition methods, our approach does not require pre-trained detectors for objects and hands. Instead we demonstrate the ability to learn a hierarchical
more » ... of an activity by exploiting the consistent appearance of objects, hands, and actions that results from the egocentric context. We show that joint modeling of activities, actions, and objects leads to superior performance in comparison to the case where they are considered independently. We introduce a novel representation of actions based on object-hand interactions and experimentally demonstrate the superior performance of our representation in comparison to standard activity representations such as bag of words. Hand Bread Hand Hand Jam Bread Spoon Hand Hand Hand Bread Peanut Spoon Hand Hand Hand Hand Hand Bread Hand Hand Bread Spoon Jam Spoon Hand Hand Bread Peanut Take Bread Scoop Jam Scoop Peanut Bu4er
doi:10.1109/iccv.2011.6126269 dblp:conf/iccv/FathiFR11 fatcat:2dlhzd5opvfixhc6xtlt5lguie

Decentralized suboptimal control via limited capacity channels

Alireza Farhadi, N.U. Ahmed
2009 2009 American Control Conference  
Farhadi is a Postdoctoral Fellow at the School of Information Technology and Engineering, University of Ottawa, Ontario. E-mail: N. U.  ... 
doi:10.1109/acc.2009.5160497 dblp:conf/amcc/FarhadiA09 fatcat:jhsvejwvm5ex5gcd57sbikw3pq

Stochastic Matching with Few Queries: New Algorithms and Tools [article]

Soheil Behnezhad and Alireza Farhadi and MohammadTaghi Hajiaghayi and Nima Reyhani
2018 arXiv   pre-print
We consider the following stochastic matching problem on both weighted and unweighted graphs: A graph G(V, E) along with a parameter p ∈ (0, 1) is given in the input. Each edge of G is realized independently with probability p. The goal is to select a degree bounded (dependent only on p) subgraph H of G such that the expected size/weight of maximum realized matching of H is close to that of G. This model of stochastic matching has attracted significant attention over the recent years due to its
more » ... various applications. The most fundamental open question is the best approximation factor achievable for such algorithms that, in the literature, are referred to as non-adaptive algorithms. Prior work has identified breaking (near) half-approximation as a barrier for both weighted and unweighted graphs. Our main results are as follows: -- We analyze a simple and clean algorithm and show that for unweighted graphs, it finds an (almost) 4√(2)-5 (≈ 0.6568) approximation by querying O( (1/p)/p) edges per vertex. This improves over the state-of-the-art 0.5001 approximate algorithm of Assadi et al. [EC'17]. -- We show that the same algorithm achieves a 0.501 approximation for weighted graphs by querying O( (1/p)/p) edges per vertex. This is the first algorithm to break 0.5 approximation barrier for weighted graphs. It also improves the per-vertex queries of the state-of-the-art by Yamaguchi and Maehara [SODA'18] and Behnezhad and Reyhani [EC'18]. Our algorithms are fundamentally different from prior works, yet are very simple and natural. For the analysis, we introduce a number of procedures that construct heavy fractional matchings. We consider the new algorithms and our analytical tools to be the main contributions of this paper.
arXiv:1811.03224v1 fatcat:ab4zydmerfgixp7bfiylbbbmra

Lower Bounds for External Memory Integer Sorting via Network Coding [article]

Alireza Farhadi, MohammadTaghi Hajiaghayi, Kasper Green Larsen, Elaine Shi
2018 arXiv   pre-print
Sorting extremely large datasets is a frequently occuring task in practice. These datasets are usually much larger than the computer's main memory; thus external memory sorting algorithms, first introduced by Aggarwal and Vitter (1988), are often used. The complexity of comparison based external memory sorting has been understood for decades by now, however the situation remains elusive if we assume the keys to be sorted are integers. In internal memory, one can sort a set of n integer keys of
more » ... ( n) bits each in O(n) time using the classic Radix Sort algorithm, however in external memory, there are no faster integer sorting algorithms known than the simple comparison based ones. In this paper, we present a tight conditional lower bound on the complexity of external memory sorting of integers. Our lower bound is based on a famous conjecture in network coding by Li and Li, who conjectured that network coding cannot help anything beyond the standard multicommodity flow rate in undirected graphs. The only previous work connecting the Li and Li conjecture to lower bounds for algorithms is due to Adler et al. Adler et al. indeed obtain relatively simple lower bounds for oblivious algorithms (the memory access pattern is fixed and independent of the input data). Unfortunately obliviousness is a strong limitations, especially for integer sorting: we show that the Li and Li conjecture implies an Ω(n n) lower bound for internal memory oblivious sorting when the keys are Θ( n) bits. This is in sharp contrast to the classic (non-oblivious) Radix Sort algorithm. Indeed going beyond obliviousness is highly non-trivial; we need to introduce several new methods and involved techniques, which are of their own interest, to obtain our tight lower bound for external memory integer sorting.
arXiv:1811.01313v1 fatcat:cvflhavz6rbefaeagsnildilxe

Almost Envy-freeness, Envy-rank, and Nash Social Welfare Matchings [article]

Alireza Farhadi, MohammadTaghi Hajiaghayi, Mohamad Latifian, Masoud Seddighin, Hadi Yami
2020 arXiv   pre-print
Envy-free up to one good (EF1) and envy-free up to any good (EFX) are two well-known extensions of envy-freeness for the case of indivisible items. It is shown that EF1 can always be guaranteed for agents with subadditive valuations. In sharp contrast, it is unknown whether or not an EFX allocation always exists, even for four agents and additive valuations. In addition, the best approximation guarantee for EFX is (ϕ -1) ≃ 0.61 by Amanitidis et al.. In order to find a middle ground to bridge
more » ... s gap, in this paper we suggest another fairness criterion, namely envy-freeness up to a random good or EFR, which is weaker than EFX, yet stronger than EF1. For this notion, we provide a polynomial-time 0.73-approximation allocation algorithm. For our algorithm, we introduce Nash Social Welfare Matching which makes a connection between Nash Social Welfare and envy freeness. We believe Nash Social Welfare Matching will find its applications in future work.
arXiv:2007.07027v1 fatcat:a3wr6btjnrfifd4gandqf3moli

Coincidence of COVID-19 epidemic and olfactory dysfunction outbreak [article]

Seyed Hamid Reza Bagheri, Ali Mohammad Asghari, Mohammad Farhadi, Ahmad Reza Shamshiri, Ali Kabir, Seyed Kamran Kamrava, Maryam Jalessi, Alireza Mohebbi, Rafieh Alizadeh, Ali Asghar Honarmand, Babak Ghalehbaghi, Alireza Salimi
2020 medRxiv   pre-print
. • Alireza Salimi, MD. Professor of anesthesiology, Shahid Beheshti University of Medical Sciences, Tehran, Iran 4-Corresponding Author: Babak Ghalehbaghi, M.D.  ... 
doi:10.1101/2020.03.23.20041889 fatcat:pnyt75s3zzfgzf6kgng2ikzife

Suboptimal decentralized control over noisy communication channels

Alireza Farhadi, N.U. Ahmed
2011 Systems & control letters (Print)  
Farhadi is a Post Doctoral Fellow at INRIA (the French national institute for research in computer science and control), Grenoble, France. This paper is a result of a research work done in Canada.  ...  Farhadi, N.U.  ... 
doi:10.1016/j.sysconle.2011.02.007 fatcat:mrxj2a2yyvgbzg47nju72njmue

Polynomial-time Approximation Scheme for Minimum k-cut in Planar and Minor-free Graphs [article]

MohammadHossein Bateni, Alireza Farhadi, MohammadTaghi Hajiaghayi
2018 arXiv   pre-print
The k-cut problem asks, given a connected graph G and a positive integer k, to find a minimum-weight set of edges whose removal splits G into k connected components. We give the first polynomial-time algorithm with approximation factor 2-ϵ (with constant ϵ > 0) for the k-cut problem in planar and minor-free graphs. Applying more complex techniques, we further improve our method and give a polynomial-time approximation scheme for the k-cut problem in both planar and minor-free graphs. Despite
more » ... sistent effort, to the best of our knowledge, this is the first improvement for the k-cut problem over standard approximation factor of 2 in any major class of graphs.
arXiv:1811.04052v1 fatcat:uz7iok25kre3baor6toekzx3iy

On the Complexity of Chore Division

Alireza Farhadi, MohammadTaghi Hajiaghayi
2018 Proceedings of the Twenty-Seventh International Joint Conference on Artificial Intelligence  
We study the proportional chore division problem where a protocol wants to divide an undesirable object, called chore, among n different players. This problem is the dual variant of the cake cutting problem in which we want to allocate a desirable object. In this paper, we show that chore division and cake cutting problems are closely related to each other and provide a tight lower bound for proportional chore division.
doi:10.24963/ijcai.2018/31 dblp:conf/ijcai/FarhadiH18 fatcat:izizdk6irbhyhnpdkbpaqdaj2i

Analysis of Network Coding in a Slotted ALOHA-based Two-Way Relay Network [article]

Alireza Mahdavi Javid, Mehdi Setayesh, Farzaneh Farhadi, Farid Ashtiani
2016 arXiv   pre-print
This paper deals with a two-way relay network (TWRN) based on a slotted ALOHA protocol which utilizes network coding to exchange the packets. We proposed an analytical approach to study the behavior of such networks and the effects of network coding on the throughput, power, and queueing delay of the relay node. In addition, when end nodes are not saturated, our approach enables us to achieve the stability region of the network in different situations. Finally, we carry out some simulation to
more » ... nfirm the validity of the proposed analytical approach.
arXiv:1602.02041v1 fatcat:skryvktkhvalbmejhwdo6ot56m

Tracking Nonlinear Noisy Dynamic Systems over Noisy Communication Channels

Alireza Farhadi, N. U. Ahmed
2011 IEEE Transactions on Communications  
This paper is concerned with tracking a vector of signal process generated by a family of distributed (geographically separated) nonlinear noisy dynamic subsystems over the binary symmetric channel. Nonlinear subsystems are subject to bounded external disturbances. Measurements are also subject to bounded noises. For this system and channel, subject to constraints on transmission rates, cross over probabilities and Lipschitz constants, a simple methodology is presented ensuring tracking with
more » ... nded mean absolute error. Index Terms-Tracking, the binary symmetric channel, the erasure channel, nonlinear systems.
doi:10.1109/tcomm.2011.020411.090488 fatcat:xx6vdmp4lzcc3oheg7m6sjyopi
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