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Documents authored by Etessami, Kousha

Document
Complete Volume
DOI: 10.4230/LIPIcs.ICALP.2023
LIPIcs, Volume 261, ICALP 2023, Complete Volume

Authors: Kousha Etessami, Uriel Feige, and Gabriele Puppis

Published in: LIPIcs, Volume 261, 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)

Abstract
LIPIcs, Volume 261, ICALP 2023, Complete Volume
Cite as

50th International Colloquium on Automata, Languages, and Programming (ICALP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 261, pp. 1-2486, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@Proceedings{etessami_et_al:LIPIcs.ICALP.2023,
  title =	{{LIPIcs, Volume 261, ICALP 2023, Complete Volume}},
  booktitle =	{50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)},
  pages =	{1--2486},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-278-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{261},
  editor =	{Etessami, Kousha and Feige, Uriel and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2023},
  URN =		{urn:nbn:de:0030-drops-180517},
  doi =		{10.4230/LIPIcs.ICALP.2023},
  annote =	{Keywords: LIPIcs, Volume 261, ICALP 2023, Complete Volume}
}
Document
Front Matter
DOI: 10.4230/LIPIcs.ICALP.2023.0
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Kousha Etessami, Uriel Feige, and Gabriele Puppis

Published in: LIPIcs, Volume 261, 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)

Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as

50th International Colloquium on Automata, Languages, and Programming (ICALP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 261, pp. 0:i-0:xxxviii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{etessami_et_al:LIPIcs.ICALP.2023.0,
  author =	{Etessami, Kousha and Feige, Uriel and Puppis, Gabriele},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)},
  pages =	{0:i--0:xxxviii},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-278-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{261},
  editor =	{Etessami, Kousha and Feige, Uriel and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2023.0},
  URN =		{urn:nbn:de:0030-drops-180523},
  doi =		{10.4230/LIPIcs.ICALP.2023.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
DOI: 10.4230/DagRep.12.1.101
Finite and Algorithmic Model Theory (Dagstuhl Seminar 22051)

Authors: Albert Atserias, Christoph Berkholz, Kousha Etessami, and Joanna Ochremiak

Published in: Dagstuhl Reports, Volume 12, Issue 1 (2022)

Abstract
Finite and algorithmic model theory (FAMT) studies the expressive power of logical languages on finite structures or, more generally, structures that can be finitely presented. These are the structures that serve as input to computation, and for this reason the study of FAMT is intimately connected with computer science. Over the last four decades, the subject has developed through a close interaction between theoretical computer science and related areas of mathematics, including logic and combinatorics. This report documents the program and the outcomes of Dagstuhl Seminar 22051 "Finite and Algorithmic Model Theory".
Cite as

Albert Atserias, Christoph Berkholz, Kousha Etessami, and Joanna Ochremiak. Finite and Algorithmic Model Theory (Dagstuhl Seminar 22051). In Dagstuhl Reports, Volume 12, Issue 1, pp. 101-118, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{atserias_et_al:DagRep.12.1.101,
  author =	{Atserias, Albert and Berkholz, Christoph and Etessami, Kousha and Ochremiak, Joanna},
  title =	{{Finite and Algorithmic Model Theory (Dagstuhl Seminar 22051)}},
  pages =	{101--118},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2022},
  volume =	{12},
  number =	{1},
  editor =	{Atserias, Albert and Berkholz, Christoph and Etessami, Kousha and Ochremiak, Joanna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.12.1.101},
  URN =		{urn:nbn:de:0030-drops-169232},
  doi =		{10.4230/DagRep.12.1.101},
  annote =	{Keywords: automata and game theory, database theory, descriptive complexity, finite model theory, homomorphism counts, Query enumeration}
}
Document
DOI: 10.4230/LIPIcs.ITCS.2020.18
Tarski’s Theorem, Supermodular Games, and the Complexity of Equilibria

Authors: Kousha Etessami, Christos Papadimitriou, Aviad Rubinstein, and Mihalis Yannakakis

Published in: LIPIcs, Volume 151, 11th Innovations in Theoretical Computer Science Conference (ITCS 2020)

Abstract
The use of monotonicity and Tarski’s theorem in existence proofs of equilibria is very widespread in economics, while Tarski’s theorem is also often used for similar purposes in the context of verification. However, there has been relatively little in the way of analysis of the complexity of finding the fixed points and equilibria guaranteed by this result. We study a computational formalism based on monotone functions on the d-dimensional grid with sides of length N, and their fixed points, as well as the closely connected subject of supermodular games and their equilibria. It is known that finding some (any) fixed point of a monotone function can be done in time log^d N, and we show it requires at least log^2 N function evaluations already on the 2-dimensional grid, even for randomized algorithms. We show that the general Tarski problem of finding some fixed point, when the monotone function is given succinctly (by a boolean circuit), is in the class PLS of problems solvable by local search and, rather surprisingly, also in the class PPAD. Finding the greatest or least fixed point guaranteed by Tarski’s theorem, however, requires d ⋅ N steps, and is NP-hard in the white box model. For supermodular games, we show that finding an equilibrium in such games is essentially computationally equivalent to the Tarski problem, and finding the maximum or minimum equilibrium is similarly harder. Interestingly, two-player supermodular games where the strategy space of one player is one-dimensional can be solved in O(log N) steps. We also show that computing (approximating) the value of Condon’s (Shapley’s) stochastic games reduces to the Tarski problem. An important open problem highlighted by this work is proving a Ω(log^d N) lower bound for small fixed dimension d ≥ 3.
Cite as

Kousha Etessami, Christos Papadimitriou, Aviad Rubinstein, and Mihalis Yannakakis. Tarski’s Theorem, Supermodular Games, and the Complexity of Equilibria. In 11th Innovations in Theoretical Computer Science Conference (ITCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 151, pp. 18:1-18:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{etessami_et_al:LIPIcs.ITCS.2020.18,
  author =	{Etessami, Kousha and Papadimitriou, Christos and Rubinstein, Aviad and Yannakakis, Mihalis},
  title =	{{Tarski’s Theorem, Supermodular Games, and the Complexity of Equilibria}},
  booktitle =	{11th Innovations in Theoretical Computer Science Conference (ITCS 2020)},
  pages =	{18:1--18:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-134-4},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{151},
  editor =	{Vidick, Thomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2020.18},
  URN =		{urn:nbn:de:0030-drops-117037},
  doi =		{10.4230/LIPIcs.ITCS.2020.18},
  annote =	{Keywords: Tarski’s theorem, supermodular games, monotone functions, lattices, fixed points, Nash equilibria, computational complexity, PLS, PPAD, stochastic games, oracle model, lower bounds}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2019.115
Reachability for Branching Concurrent Stochastic Games (Track B: Automata, Logic, Semantics, and Theory of Programming)

Authors: Kousha Etessami, Emanuel Martinov, Alistair Stewart, and Mihalis Yannakakis

Published in: LIPIcs, Volume 132, 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019)

Abstract
We give polynomial time algorithms for deciding almost-sure and limit-sure reachability in Branching Concurrent Stochastic Games (BCSGs). These are a class of infinite-state imperfect-information stochastic games that generalize both finite-state concurrent stochastic reachability games ([L. de Alfaro et al., 2007]) and branching simple stochastic reachability games ([K. Etessami et al., 2018]).
Cite as

Kousha Etessami, Emanuel Martinov, Alistair Stewart, and Mihalis Yannakakis. Reachability for Branching Concurrent Stochastic Games (Track B: Automata, Logic, Semantics, and Theory of Programming). In 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 132, pp. 115:1-115:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{etessami_et_al:LIPIcs.ICALP.2019.115,
  author =	{Etessami, Kousha and Martinov, Emanuel and Stewart, Alistair and Yannakakis, Mihalis},
  title =	{{Reachability for Branching Concurrent Stochastic Games}},
  booktitle =	{46th International Colloquium on Automata, Languages, and Programming (ICALP 2019)},
  pages =	{115:1--115:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-109-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{132},
  editor =	{Baier, Christel and Chatzigiannakis, Ioannis and Flocchini, Paola and Leonardi, Stefano},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2019.115},
  URN =		{urn:nbn:de:0030-drops-106917},
  doi =		{10.4230/LIPIcs.ICALP.2019.115},
  annote =	{Keywords: stochastic games, multi-type branching processes, concurrent games, minimax-polynomial equations, reachability, almost-sure, limit-sure}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.STACS.2013.1
The complexity of analyzing infinite-state Markov chains, Markov decision processes, and stochastic games (Invited Talk)

Authors: Kousha Etessami

Published in: LIPIcs, Volume 20, 30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013)

Abstract
In recent years, a considerable amount of research has been devoted to understanding the computational complexity of basic analysis problems, and model checking problems, for finitely-presented countable infinite-state probabilistic systems. In particular, we have studied recursive Markov chains (RMCs), recursive Markov decision processes (RMDPs) and recursive stochastic games (RSGs). These arise by adding a natural recursion feature to finite-state Markov chains, MDPs, and stochastic games. RMCs and RMDPs provide natural abstract models of probabilistic procedural programs with recursion, and they are expressively equivalent to probabilistic and MDP extensions of pushdown automata. Moreover, a number of well-studied stochastic processes, including multi-type branching processes, (discrete-time) quasi-birth-death processes, and stochastic context-free grammars, can be suitably captured by subclasses of RMCs. A central computational problem for analyzing various classes of recursive probabilistic systems is the computation of their (optimal) termination probabilities. These form a key ingredient for many other analyses, including model checking. For RMCs, and for important subclasses of RMDPs and RSGs, computing their termination values is equivalent to computing the least fixed point (LFP) solution of a corresponding monotone system of polynomial (min/max) equations. The complexity of computing the LFP solution for such equation systems is a intriguing problem, with connections to several areas of research. The LFP solution may in general be irrational. So, one possible aim is to compute it to within a desired additive error epsilon > 0. For general RMCs, approximating their termination probability within any non-trivial constant additive error < 1/2, is at least as hard as long-standing open problems in the complexity of numerical computation which are not even known to be in NP. For several key subclasses of RMCs and RMDPs, computing their termination values turns out to be much more tractable. In this talk I will survey algorithms for, and discuss the computational complexity of, key analysis problems for classes of infinite-state recursive MCs, MDPs, and stochastic games. In particular, I will discuss recent joint work with Alistair Stewart and Mihalis Yannakakis (in papers that appeared at STOC'12 and ICALP'12), in which we have obtained polynomial time algorithms for computing, to within arbitrary desired precision, the LFP solution of probabilistic polynomial (min/max) systems of equations. Using this, we obtained the first P-time algorithms for computing (within desired precision) the extinction probabilities of multi-type branching processes, the probability that an arbitrary given stochastic context-free grammar generates a given string, and the optimum (maximum or minimum) extinction probabilities for branching MDPs and context-free MDPs. For branching MDPs, their corresponding equations amount to Bellman optimality equations for minimizing/maximizing their termination probabilities. Our algorithms combine variations and generalizations of Newton's method with other techniques, including linear programming. The algorithms are fairly easy to implement, but analyzing their worst-case running time is mathematically quite involved.
Cite as

Kousha Etessami. The complexity of analyzing infinite-state Markov chains, Markov decision processes, and stochastic games (Invited Talk). In 30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 20, pp. 1-2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

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@InProceedings{etessami:LIPIcs.STACS.2013.1,
  author =	{Etessami, Kousha},
  title =	{{The complexity of analyzing infinite-state Markov chains, Markov decision processes, and stochastic games}},
  booktitle =	{30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013)},
  pages =	{1--2},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-50-7},
  ISSN =	{1868-8969},
  year =	{2013},
  volume =	{20},
  editor =	{Portier, Natacha and Wilke, Thomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2013.1},
  URN =		{urn:nbn:de:0030-drops-39143},
  doi =		{10.4230/LIPIcs.STACS.2013.1},
  annote =	{Keywords: recursive Markov chains, Markov decision processes, stochastic games, monotone systems of nonlinear equations, least fixed points, Newton's method, co}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2010.108
One-Counter Stochastic Games

Authors: Tomás Brázdil, Václav Brozek, and Kousha Etessami

Published in: LIPIcs, Volume 8, IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2010)

Abstract
We study the computational complexity of basic decision problems for one-counter simple stochastic games (OC-SSGs), under various objectives. OC-SSGs are 2-player turn-based stochastic games played on the transition graph of classic one-counter automata. We study primarily the termination objective, where the goal of one player is to maximize the probability of reaching counter value 0, while the other player wishes to avoid this. Partly motivated by the goal of understanding termination objectives, we also study certain ``limit'' and ``long run average'' reward objectives that are closely related to some well-studied objectives for stochastic games with rewards. Examples of problems we address include: does player 1 have a strategy to ensure that the counter eventually hits 0, i.e., terminates, almost surely, regardless of what player 2 does? Or that the $liminf$ (or $limsup$) counter value equals $infty$ with a desired probability? Or that the long run average reward is $>0$ with desired probability? We show that the qualitative termination problem for OC-SSGs is in $NP$ intersect $coNP$, and is in P-time for 1-player OC-SSGs, or equivalently for one-counter Markov Decision Processes (OC-MDPs). Moreover, we show that quantitative limit problems for OC-SSGs are in $NP$ intersect $coNP$, and are in P-time for 1-player OC-MDPs. Both qualitative limit problems and qualitative termination problems for OC-SSGs are already at least as hard as Condon's quantitative decision problem for finite-state SSGs.
Cite as

Tomás Brázdil, Václav Brozek, and Kousha Etessami. One-Counter Stochastic Games. In IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2010). Leibniz International Proceedings in Informatics (LIPIcs), Volume 8, pp. 108-119, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{brazdil_et_al:LIPIcs.FSTTCS.2010.108,
  author =	{Br\'{a}zdil, Tom\'{a}s and Brozek, V\'{a}clav and Etessami, Kousha},
  title =	{{One-Counter Stochastic Games}},
  booktitle =	{IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2010)},
  pages =	{108--119},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-23-1},
  ISSN =	{1868-8969},
  year =	{2010},
  volume =	{8},
  editor =	{Lodaya, Kamal and Mahajan, Meena},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2010.108},
  URN =		{urn:nbn:de:0030-drops-28571},
  doi =		{10.4230/LIPIcs.FSTTCS.2010.108},
  annote =	{Keywords: one-counter automata, simple stochastic games, Markov decision process, termination, limit, long run average reward}
}
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