41 Search Results for "Reischuk, R�diger"

Document
DOI: 10.4230/LIPIcs.OPODIS.2022.16
New Dolev-Reischuk Lower Bounds Meet Blockchain Eclipse Attacks

Authors: Ittai Abraham and Gilad Stern

Published in: LIPIcs, Volume 253, 26th International Conference on Principles of Distributed Systems (OPODIS 2022)

Abstract
In 1985, Dolev and Reischuk proved a fundamental communication lower bounds on protocols achieving fault tolerant synchronous broadcast and consensus: any deterministic protocol solving those tasks (even against omission faults) requires at least a quadratic number of messages to be sent by nonfaulty parties. In contrast, many blockchain systems achieve consensus with seemingly linear communication per instance against Byzantine faults. We explore this dissonance in three main ways. First, we extend the Dolev-Reischuk family of lower bounds and prove a new lower bound for Crusader Broadcast protocols. Our lower bound for crusader broadcast requires non-trivial extensions and a much stronger Byzantine adversary with the ability to simulate honest parties. Secondly, we extend our lower bounds to all-but-m Crusader Broadcast, in which up to m parties are allowed to output a different value. Finally, we discuss the ways in which these lower bounds relate to the security of blockchain systems. We show how Eclipse-style attacks in such systems can be viewed as specific instances of the attacks used in our lower bound for Crusader Broadcast. This connection suggests a more systematic way of analyzing and reasoning about Eclipse-style attacks through the lens of the Dolev-Reischuk family of attacks.
Cite as

Ittai Abraham and Gilad Stern. New Dolev-Reischuk Lower Bounds Meet Blockchain Eclipse Attacks. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 16:1-16:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{abraham_et_al:LIPIcs.OPODIS.2022.16,
  author =	{Abraham, Ittai and Stern, Gilad},
  title =	{{New Dolev-Reischuk Lower Bounds Meet Blockchain Eclipse Attacks}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{16:1--16:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-265-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{253},
  editor =	{Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.16},
  URN =		{urn:nbn:de:0030-drops-176368},
  doi =		{10.4230/LIPIcs.OPODIS.2022.16},
  annote =	{Keywords: consensus, crusader broadcast, Byzantine fault tolerance, blockchain, synchrony, lower bounds}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.18
Make Every Word Count: Adaptive Byzantine Agreement with Fewer Words

Authors: Shir Cohen, Idit Keidar, and Alexander Spiegelman

Published in: LIPIcs, Volume 253, 26th International Conference on Principles of Distributed Systems (OPODIS 2022)

Abstract
Byzantine Agreement (BA) is a key component in many distributed systems. While Dolev and Reischuk have proven a long time ago that quadratic communication complexity is necessary for worst-case runs, the question of what can be done in practically common runs with fewer failures remained open. In this paper we present the first Byzantine Broadcast algorithm with O(n(f+1)) communication complexity in a model with resilience of n = 2t+1, where 0 ≤ f ≤ t is the actual number of process failures in a run. And for BA with strong unanimity, we present the first optimal-resilience algorithm that has linear communication complexity in the failure-free case and a quadratic cost otherwise.
Cite as

Shir Cohen, Idit Keidar, and Alexander Spiegelman. Make Every Word Count: Adaptive Byzantine Agreement with Fewer Words. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 18:1-18:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{cohen_et_al:LIPIcs.OPODIS.2022.18,
  author =	{Cohen, Shir and Keidar, Idit and Spiegelman, Alexander},
  title =	{{Make Every Word Count: Adaptive Byzantine Agreement with Fewer Words}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{18:1--18:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-265-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{253},
  editor =	{Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.18},
  URN =		{urn:nbn:de:0030-drops-176385},
  doi =		{10.4230/LIPIcs.OPODIS.2022.18},
  annote =	{Keywords: Byzantine Agreement, Byzantine Broadcast, Adaptive communication}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.14
Byzantine Consensus Is Θ(n²): The Dolev-Reischuk Bound Is Tight Even in Partial Synchrony!

Authors: Pierre Civit, Muhammad Ayaz Dzulfikar, Seth Gilbert, Vincent Gramoli, Rachid Guerraoui, Jovan Komatovic, and Manuel Vidigueira

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
The Dolev-Reischuk bound says that any deterministic Byzantine consensus protocol has (at least) quadratic communication complexity in the worst case. While it has been shown that the bound is tight in synchronous environments, it is still unknown whether a consensus protocol with quadratic communication complexity can be obtained in partial synchrony. Until now, the most efficient known solutions for Byzantine consensus in partially synchronous settings had cubic communication complexity (e.g., HotStuff, binary DBFT). This paper closes the existing gap by introducing SQuad, a partially synchronous Byzantine consensus protocol with quadratic worst-case communication complexity. In addition, SQuad is optimally-resilient and achieves linear worst-case latency complexity. The key technical contribution underlying SQuad lies in the way we solve view synchronization, the problem of bringing all correct processes to the same view with a correct leader for sufficiently long. Concretely, we present RareSync, a view synchronization protocol with quadratic communication complexity and linear latency complexity, which we utilize in order to obtain SQuad.
Cite as

Pierre Civit, Muhammad Ayaz Dzulfikar, Seth Gilbert, Vincent Gramoli, Rachid Guerraoui, Jovan Komatovic, and Manuel Vidigueira. Byzantine Consensus Is Θ(n²): The Dolev-Reischuk Bound Is Tight Even in Partial Synchrony!. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 14:1-14:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{civit_et_al:LIPIcs.DISC.2022.14,
  author =	{Civit, Pierre and Dzulfikar, Muhammad Ayaz and Gilbert, Seth and Gramoli, Vincent and Guerraoui, Rachid and Komatovic, Jovan and Vidigueira, Manuel},
  title =	{{Byzantine Consensus Is \Theta(n²): The Dolev-Reischuk Bound Is Tight Even in Partial Synchrony!}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{14:1--14:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.14},
  URN =		{urn:nbn:de:0030-drops-172059},
  doi =		{10.4230/LIPIcs.DISC.2022.14},
  annote =	{Keywords: Optimal Byzantine consensus, Communication complexity, Latency complexity}
}
Document
DOI: 10.4230/LIPIcs.IPEC.2021.7
Dynamic Kernels for Hitting Sets and Set Packing

Authors: Max Bannach, Zacharias Heinrich, Rüdiger Reischuk, and Till Tantau

Published in: LIPIcs, Volume 214, 16th International Symposium on Parameterized and Exact Computation (IPEC 2021)

Abstract
Computing small kernels for the hitting set problem is a well-studied computational problem where we are given a hypergraph with n vertices and m hyperedges, each of size d for some small constant d, and a parameter k. The task is to compute a new hypergraph, called a kernel, whose size is polynomial with respect to the parameter k and which has a size-k hitting set if, and only if, the original hypergraph has one. State-of-the-art algorithms compute kernels of size k^d (which is a polynomial kernel size as d is a constant), and they do so in time m⋅ 2^d poly(d) for a small polynomial poly(d) (which is a linear runtime as d is again a constant). We generalize this task to the dynamic setting where hyperedges may continuously be added or deleted and one constantly has to keep track of a size-k^d hitting set kernel in memory (including moments when no size-k hitting set exists). This paper presents a deterministic solution with worst-case time 3^d poly(d) for updating the kernel upon hyperedge inserts and time 5^d poly(d) for updates upon deletions. These bounds nearly match the time 2^d poly(d) needed by the best static algorithm per hyperedge. Let us stress that for constant d our algorithm maintains a dynamic hitting set kernel with constant, deterministic, worst-case update time that is independent of n, m, and the parameter k. As a consequence, we also get a deterministic dynamic algorithm for keeping track of size-k hitting sets in d-hypergraphs with update times O(1) and query times O(c^k) where c = d - 1 + O(1/d) equals the best base known for the static setting.
Cite as

Max Bannach, Zacharias Heinrich, Rüdiger Reischuk, and Till Tantau. Dynamic Kernels for Hitting Sets and Set Packing. In 16th International Symposium on Parameterized and Exact Computation (IPEC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 214, pp. 7:1-7:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bannach_et_al:LIPIcs.IPEC.2021.7,
  author =	{Bannach, Max and Heinrich, Zacharias and Reischuk, R\"{u}diger and Tantau, Till},
  title =	{{Dynamic Kernels for Hitting Sets and Set Packing}},
  booktitle =	{16th International Symposium on Parameterized and Exact Computation (IPEC 2021)},
  pages =	{7:1--7:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-216-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{214},
  editor =	{Golovach, Petr A. and Zehavi, Meirav},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2021.7},
  URN =		{urn:nbn:de:0030-drops-153900},
  doi =		{10.4230/LIPIcs.IPEC.2021.7},
  annote =	{Keywords: Kernelization, Dynamic Algorithms, Hitting Set, Set Packings}
}
Document
DOI: 10.4230/LIPIcs.DISC.2021.32
Optimal Communication Complexity of Authenticated Byzantine Agreement

Authors: Atsuki Momose and Ling Ren

Published in: LIPIcs, Volume 209, 35th International Symposium on Distributed Computing (DISC 2021)

Abstract
Byzantine Agreement (BA) is one of the most fundamental problems in distributed computing, and its communication complexity is an important efficiency metric. It is well known that quadratic communication is necessary for BA in the worst case due to a lower bound by Dolev and Reischuk. This lower bound has been shown to be tight for the unauthenticated setting with f < n/3 by Berman et al. but a considerable gap remains for the authenticated setting with n/3 ≤ f < n/2. This paper provides two results towards closing this gap. Both protocols have a quadratic communication complexity and have different trade-offs in resilience and assumptions. The first protocol achieves the optimal resilience of f < n/2 but requires a trusted setup for threshold signature. The second protocol achieves near optimal resilience f ≤ (1/2 - ε)n in the standard PKI model.
Cite as

Atsuki Momose and Ling Ren. Optimal Communication Complexity of Authenticated Byzantine Agreement. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 32:1-32:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{momose_et_al:LIPIcs.DISC.2021.32,
  author =	{Momose, Atsuki and Ren, Ling},
  title =	{{Optimal Communication Complexity of Authenticated Byzantine Agreement}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{32:1--32:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-210-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{209},
  editor =	{Gilbert, Seth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.32},
  URN =		{urn:nbn:de:0030-drops-148341},
  doi =		{10.4230/LIPIcs.DISC.2021.32},
  annote =	{Keywords: Byzantine Agreement, Communication Complexity, Lower Bound}
}
Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2020.92
Nondeterministic and Randomized Boolean Hierarchies in Communication Complexity

Authors: Toniann Pitassi, Morgan Shirley, and Thomas Watson

Published in: LIPIcs, Volume 168, 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)

Abstract
We investigate the power of randomness in two-party communication complexity. In particular, we study the model where the parties can make a constant number of queries to a function with an efficient one-sided-error randomized protocol. The complexity classes defined by this model comprise the Randomized Boolean Hierarchy, which is analogous to the Boolean Hierarchy but defined with one-sided-error randomness instead of nondeterminism. Our techniques connect the Nondeterministic and Randomized Boolean Hierarchies, and we provide a complete picture of the relationships among complexity classes within and across these two hierarchies. In particular, we prove that the Randomized Boolean Hierarchy does not collapse, and we prove a query-to-communication lifting theorem for all levels of the Nondeterministic Boolean Hierarchy and use it to resolve an open problem stated in the paper by Halstenberg and Reischuk (CCC 1988) which initiated the study of this hierarchy.
Cite as

Toniann Pitassi, Morgan Shirley, and Thomas Watson. Nondeterministic and Randomized Boolean Hierarchies in Communication Complexity. In 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 168, pp. 92:1-92:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{pitassi_et_al:LIPIcs.ICALP.2020.92,
  author =	{Pitassi, Toniann and Shirley, Morgan and Watson, Thomas},
  title =	{{Nondeterministic and Randomized Boolean Hierarchies in Communication Complexity}},
  booktitle =	{47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)},
  pages =	{92:1--92:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-138-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{168},
  editor =	{Czumaj, Artur and Dawar, Anuj and Merelli, Emanuela},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2020.92},
  URN =		{urn:nbn:de:0030-drops-124992},
  doi =		{10.4230/LIPIcs.ICALP.2020.92},
  annote =	{Keywords: Boolean hierarchies, lifting theorems, query complexity}
}
Document
DOI: 10.4230/DagRep.4.3.62
Computational Complexity of Discrete Problems (Dagstuhl Seminar 14121)

Authors: Anna Gal, Michal Koucky, Oded Regev, and Rüdiger Reischuk

Published in: Dagstuhl Reports, Volume 4, Issue 3 (2014)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 14121 "Computational Complexity of Discrete Problems". The first section gives an overview of the topics covered and the organization of the meeting. Section 2 lists the talks given in chronological order. The last section contains the abstracts of the talks.
Cite as

Anna Gal, Michal Koucky, Oded Regev, and Rüdiger Reischuk. Computational Complexity of Discrete Problems (Dagstuhl Seminar 14121). In Dagstuhl Reports, Volume 4, Issue 3, pp. 62-84, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@Article{gal_et_al:DagRep.4.3.62,
  author =	{Gal, Anna and Koucky, Michal and Regev, Oded and Reischuk, R\"{u}diger},
  title =	{{Computational Complexity of Discrete Problems (Dagstuhl Seminar 14121)}},
  pages =	{62--84},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2014},
  volume =	{4},
  number =	{3},
  editor =	{Gal, Anna and Koucky, Michal and Regev, Oded and Reischuk, R\"{u}diger},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagRep.4.3.62},
  URN =		{urn:nbn:de:0030-drops-45921},
  doi =		{10.4230/DagRep.4.3.62},
  annote =	{Keywords: discrete problems, computational complexity, Turing machines, Boolean circuits, arithmetic circuits, quantum computing, communication complexity, pseudorandomness, derandomization, approximation, data streams}
}
Document
DOI: 10.4230/DagSemProc.08381.4
Depth Reduction for Circuits with a Single Layer of Modular Counting Gates

Authors: Kristoffer Arnsfelt Hansen

Published in: Dagstuhl Seminar Proceedings, Volume 8381, Computational Complexity of Discrete Problems (2008)

Abstract
We consider the class of constant depth AND/OR circuits augmented with a layer of modular counting gates at the bottom layer, i.e ${AC}^0 circ {MOD}_m$ circuits. We show that the following holds for several types of gates $G$: by adding a gate of type $G$ at the output, it is possible to obtain an equivalent randomized depth 2 circuit of quasipolynomial size consisting of a gate of type $G$ at the output and a layer of modular counting gates, i.e $G circ {MOD}_m$ circuits. The types of gates $G$ we consider are modular counting gates and threshold-style gates. For all of these, strong lower bounds are known for (deterministic) $G circ {MOD}_m$ circuits.
Cite as

Kristoffer Arnsfelt Hansen. Depth Reduction for Circuits with a Single Layer of Modular Counting Gates. In Computational Complexity of Discrete Problems. Dagstuhl Seminar Proceedings, Volume 8381, pp. 1-11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{hansen:DagSemProc.08381.4,
  author =	{Hansen, Kristoffer Arnsfelt},
  title =	{{Depth Reduction for Circuits with a Single Layer of Modular Counting Gates}},
  booktitle =	{Computational Complexity of Discrete Problems},
  pages =	{1--11},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8381},
  editor =	{Peter Bro Miltersen and R\"{u}diger Reischuk and Georg Schnitger and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08381.4},
  URN =		{urn:nbn:de:0030-drops-17824},
  doi =		{10.4230/DagSemProc.08381.4},
  annote =	{Keywords: Boolean Circuits, Randomized Polynomials, Fourier sums}
}
Document
DOI: 10.4230/DagSemProc.08381.6
Understanding space in resolution: optimal lower bounds and exponential trade-offs

Authors: Eli Ben-Sasson and Jakob Nordström

Published in: Dagstuhl Seminar Proceedings, Volume 8381, Computational Complexity of Discrete Problems (2008)

Abstract
We continue the study of tradeoffs between space and length of resolution proofs and focus on two new results: begin{enumerate} item We show that length and space in resolution are uncorrelated. This is proved by exhibiting families of CNF formulas of size $O(n)$ that have proofs of length $O(n)$ but require space $Omega(n / log n)$. Our separation is the strongest possible since any proof of length $O(n)$ can always be transformed into a proof in space $O(n / log n)$, and improves previous work reported in [Nordstr"{o}m 2006, Nordstr"{o}m and H{aa}stad 2008]. item We prove a number of trade-off results for space in the range from constant to $O(n / log n)$, most of them superpolynomial or even exponential. This is a dramatic improvement over previous results in [Ben-Sasson 2002, Hertel and Pitassi 2007, Nordstr"{o}m 2007]. end{enumerate} The key to our results is the following, somewhat surprising, theorem: Any CNF formula $F$ can be transformed by simple substitution transformation into a new formula $F'$ such that if $F$ has the right properties, $F'$ can be proven in resolution in essentially the same length as $F$ but the minimal space needed for $F'$ is lower-bounded by the number of variables that have to be mentioned simultaneously in any proof for $F$. Applying this theorem to so-called pebbling formulas defined in terms of pebble games over directed acyclic graphs and analyzing black-white pebbling on these graphs yields our results.
Cite as

Eli Ben-Sasson and Jakob Nordström. Understanding space in resolution: optimal lower bounds and exponential trade-offs. In Computational Complexity of Discrete Problems. Dagstuhl Seminar Proceedings, Volume 8381, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{bensasson_et_al:DagSemProc.08381.6,
  author =	{Ben-Sasson, Eli and Nordstr\"{o}m, Jakob},
  title =	{{Understanding space in resolution: optimal lower bounds and exponential trade-offs}},
  booktitle =	{Computational Complexity of Discrete Problems},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8381},
  editor =	{Peter Bro Miltersen and R\"{u}diger Reischuk and Georg Schnitger and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08381.6},
  URN =		{urn:nbn:de:0030-drops-17815},
  doi =		{10.4230/DagSemProc.08381.6},
  annote =	{Keywords: Proof complexity, Resolution, Pebbling.}
}
Document
DOI: 10.4230/DagSemProc.08381.1
08381 Abstracts Collection – Computational Complexity of Discrete Problems

Authors: Peter Bro Miltersen, Rüdiger Reischuk, Georg Schnitger, and Dieter van Melkebeek

Published in: Dagstuhl Seminar Proceedings, Volume 8381, Computational Complexity of Discrete Problems (2008)

Abstract
From the 14th of September to the 19th of September, the Dagstuhl Seminar 08381 ``Computational Complexity of Discrete Problems'' was held in Schloss Dagstuhl - Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work as well as open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this report. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Peter Bro Miltersen, Rüdiger Reischuk, Georg Schnitger, and Dieter van Melkebeek. 08381 Abstracts Collection – Computational Complexity of Discrete Problems. In Computational Complexity of Discrete Problems. Dagstuhl Seminar Proceedings, Volume 8381, pp. 1-18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{miltersen_et_al:DagSemProc.08381.1,
  author =	{Miltersen, Peter Bro and Reischuk, R\"{u}diger and Schnitger, Georg and van Melkebeek, Dieter},
  title =	{{08381 Abstracts Collection – Computational Complexity of Discrete Problems}},
  booktitle =	{Computational Complexity of Discrete Problems},
  pages =	{1--18},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8381},
  editor =	{Peter Bro Miltersen and R\"{u}diger Reischuk and Georg Schnitger and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08381.1},
  URN =		{none},
  doi =		{10.4230/DagSemProc.08381.1},
  annote =	{Keywords: Computational complexity, discrete problems, Turing machines, circuits, proof complexity, pseudorandomness, derandomization, cryptography, computational learning, communication complexity, query complexity, hardness of approximation}
}
Document
DOI: 10.4230/DagSemProc.08381.2
08381 Executive Summary – Computational Complexity of Discrete Problems

Authors: Peter Bro Miltersen, Rüdiger Reischuk, Georg Schnitger, and Dieter van Melkebeek

Published in: Dagstuhl Seminar Proceedings, Volume 8381, Computational Complexity of Discrete Problems (2008)

Abstract
Estimating the computational complexity of discrete problems constitutes one of the central and classical topics in the theory of computation. Mathematicians and computer scientists have long tried to classify natural families of Boolean relations according to fundamental complexity measures like time and space, both in the uniform and in the nonuniform setting. Several models of computation have been developed in order to capture the various capabilities of digital computing devices, including parallelism, randomness, and quantum interference.
Cite as

Peter Bro Miltersen, Rüdiger Reischuk, Georg Schnitger, and Dieter van Melkebeek. 08381 Executive Summary – Computational Complexity of Discrete Problems. In Computational Complexity of Discrete Problems. Dagstuhl Seminar Proceedings, Volume 8381, pp. 1-7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{miltersen_et_al:DagSemProc.08381.2,
  author =	{Miltersen, Peter Bro and Reischuk, R\"{u}diger and Schnitger, Georg and van Melkebeek, Dieter},
  title =	{{08381 Executive Summary – Computational Complexity of Discrete Problems}},
  booktitle =	{Computational Complexity of Discrete Problems},
  pages =	{1--7},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8381},
  editor =	{Peter Bro Miltersen and R\"{u}diger Reischuk and Georg Schnitger and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08381.2},
  URN =		{urn:nbn:de:0030-drops-17789},
  doi =		{10.4230/DagSemProc.08381.2},
  annote =	{Keywords: Computational complexity, discrete problems, Turing machines, circuits, proof complexity, pseudorandomness, derandomization, cryptography, computational learning, communication complexity, query complexity, hardness of approximation}
}
Document
DOI: 10.4230/DagSemProc.08381.3
Approximation norms and duality for communication complexity lower bounds

Authors: Troy Lee and Adi Shraibman

Published in: Dagstuhl Seminar Proceedings, Volume 8381, Computational Complexity of Discrete Problems (2008)

Abstract
Abstract: We will discuss a general norm based framework for showing lower bounds on communication complexity. An advantage of this approach is that one can use duality theory to obtain a lower bound quantity phrased as a maximization problem, which can be more convenient to work with in showing lower bounds. We discuss two applications of this approach. 1. The approximation rank of a matrix A is the minimum rank of a matrix close to A in ell_infty norm. The logarithm of approximation rank lower bounds quantum communication complexity and is one of the most powerful techniques available, albeit difficult to compute in practice. We show that an approximation norm known as gamma_2 is polynomially related to approximation rank. This results in a polynomial time algorithm to approximate approximation rank, and also shows that the logarithm of approximation rank lower bounds quantum communication complexity even with entanglement which was previously not known. 2. By means of an approximation norm which lower bounds multiparty number-on-the-forehead complexity, we show non-trivial lower bounds on the complexity of the disjointness function for up to c log log n players, c <1.
Cite as

Troy Lee and Adi Shraibman. Approximation norms and duality for communication complexity lower bounds. In Computational Complexity of Discrete Problems. Dagstuhl Seminar Proceedings, Volume 8381, pp. 1-9, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{lee_et_al:DagSemProc.08381.3,
  author =	{Lee, Troy and Shraibman, Adi},
  title =	{{Approximation norms and duality for communication complexity lower bounds}},
  booktitle =	{Computational Complexity of Discrete Problems},
  pages =	{1--9},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8381},
  editor =	{Peter Bro Miltersen and R\"{u}diger Reischuk and Georg Schnitger and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08381.3},
  URN =		{urn:nbn:de:0030-drops-17768},
  doi =		{10.4230/DagSemProc.08381.3},
  annote =	{Keywords: Communication complexity, lower bounds}
}
Document
DOI: 10.4230/DagSemProc.08381.5
Fast polynomial factorization and modular composition

Authors: Kiran Kedlaya and Christopher Umans

Published in: Dagstuhl Seminar Proceedings, Volume 8381, Computational Complexity of Discrete Problems (2008)

Abstract
We obtain randomized algorithms for factoring degree $n$ univariate polynomials over $F_q$ requiring $O(n^{1.5 + o(1)} log^{1+o(1)} q+ n^{1 + o(1)}log^{2+o(1)} q)$ bit operations. When $log q < n$, this is asymptotically faster than the best previous algorithms (von zur Gathen & Shoup (1992) and Kaltofen & Shoup (1998)); for $log q ge n$, it matches the asymptotic running time of the best known algorithms. The improvements come from new algorithms for modular composition of degree $n$ univariate polynomials, which is the asymptotic bottleneck in fast algorithms for factoring polynomials over finite fields. The best previous algorithms for modular composition use $O(n^{(omega + 1)/2})$ field operations, where $omega$ is the exponent of matrix multiplication (Brent & Kung (1978)), with a slight improvement in the exponent achieved by employing fast rectangular matrix multiplication (Huang & Pan (1997)). We show that modular composition and multipoint evaluation of multivariate polynomials are essentially equivalent, in the sense that an algorithm for one achieving exponent $alpha$ implies an algorithm for the other with exponent $alpha + o(1)$, and vice versa. We then give two new algorithms that solve the problem optimally (up to lower order terms): an algebraic algorithm for fields of characteristic at most $n^{o(1)}$, and a nonalgebraic algorithm that works in arbitrary characteristic. The latter algorithm works by lifting to characteristic 0, applying a small number of rounds of {em multimodular reduction}, and finishing with a small number of multidimensional FFTs. The final evaluations are reconstructed using the Chinese Remainder Theorem. As a bonus, this algorithm produces a very efficient data structure supporting polynomial evaluation queries, which is of independent interest. Our algorithms use techniques which are commonly employed in practice, so they may be competitive for real problem sizes. This contrasts with all previous subquadratic algorithsm for these problems, which rely on fast matrix multiplication. This is joint work with Kiran Kedlaya.
Cite as

Kiran Kedlaya and Christopher Umans. Fast polynomial factorization and modular composition. In Computational Complexity of Discrete Problems. Dagstuhl Seminar Proceedings, Volume 8381, pp. 1-33, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{kedlaya_et_al:DagSemProc.08381.5,
  author =	{Kedlaya, Kiran and Umans, Christopher},
  title =	{{Fast polynomial factorization and modular composition}},
  booktitle =	{Computational Complexity of Discrete Problems},
  pages =	{1--33},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8381},
  editor =	{Peter Bro Miltersen and R\"{u}diger Reischuk and Georg Schnitger and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08381.5},
  URN =		{urn:nbn:de:0030-drops-17771},
  doi =		{10.4230/DagSemProc.08381.5},
  annote =	{Keywords: Modular composition; polynomial factorization; multipoint evaluation; Chinese Remaindering}
}
Document
DOI: 10.4230/DagSemProc.08131.6
GoPubMed: Exploring Pubmed with Ontological Background Knowledge

Authors: Heiko Dietze, Dimitra Alexopoulou, Michael R. Alvers, Bill Barrio-Alvers, Andreas Doms, Jörg Hakenberg, Jan Mönnich, Conrad Plake, Andreas Reischuck, Loic Royer, Thomas Wächter, Matthias Zschunke, and Michael Schroeder

Published in: Dagstuhl Seminar Proceedings, Volume 8131, Ontologies and Text Mining for Life Sciences : Current Status and Future Perspectives (2008)

Abstract
With the ever increasing size of scientific literature, finding relevant documents and answering questions has become even more of a challenge. Recently, ontologies - hierarchical, controlled vocabularies - have been introduced to annotate genomic data. They can also improve the question answering and the selection of relevant documents in the literature search. Search engines such as GoPubMed.org use ontological background knowledge to give an overview over large query results and to help answering questions. We review the problems and solutions underlying these next generation intelligent search engines and give examples of the power of this new search paradigm.
Cite as

Heiko Dietze, Dimitra Alexopoulou, Michael R. Alvers, Bill Barrio-Alvers, Andreas Doms, Jörg Hakenberg, Jan Mönnich, Conrad Plake, Andreas Reischuk, Loic Royer, Thomas Wächter, Matthias Zschunke, and Michael Schroeder. GoPubMed: Exploring Pubmed with Ontological Background Knowledge. In Ontologies and Text Mining for Life Sciences : Current Status and Future Perspectives. Dagstuhl Seminar Proceedings, Volume 8131, p. 1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{dietze_et_al:DagSemProc.08131.6,
  author =	{Dietze, Heiko and Alexopoulou, Dimitra and Alvers, Michael R. and Barrio-Alvers, Bill and Doms, Andreas and Hakenberg, J\"{o}rg and M\"{o}nnich, Jan and Plake, Conrad and Reischuck, Andreas and Royer, Loic and W\"{a}chter, Thomas and Zschunke, Matthias and Schroeder, Michael},
  title =	{{GoPubMed: Exploring Pubmed with Ontological Background Knowledge}},
  booktitle =	{Ontologies and Text Mining for Life Sciences : Current Status and Future Perspectives},
  pages =	{1--1},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8131},
  editor =	{Michael Ashburner and Ulf Leser and Dietrich Rebholz-Schuhmann},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.08131.6},
  URN =		{urn:nbn:de:0030-drops-15204},
  doi =		{10.4230/DagSemProc.08131.6},
  annote =	{Keywords: Text mining, literature search, Gene Ontology, NLP, ontology, thesaurus, PubMed}
}
Document
DOI: 10.4230/DagSemProc.06111.2
06111 Executive Summary – Complexity of Boolean Functions

Authors: Matthias Krause, Dieter van Melkebeek, Pavel Pudlák, and Rüdiger Reischuk

Published in: Dagstuhl Seminar Proceedings, Volume 6111, Complexity of Boolean Functions (2006)

Abstract
We briefly describe the state of the art concerning the complexity of discrete functions. Computational models and analytical techniques are summarized. After describing the formal organization of the Dagstuhl seminar "Complexity of Boolean Functions" held in March 2006, we introduce the different topics that have been discussed there and mention some of the major achievements. The summary closes with an outlook on the development of discrete computational complexity in the future.
Cite as

Matthias Krause, Dieter van Melkebeek, Pavel Pudlák, and Rüdiger Reischuk. 06111 Executive Summary – Complexity of Boolean Functions. In Complexity of Boolean Functions. Dagstuhl Seminar Proceedings, Volume 6111, pp. 1-5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2006)

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@InProceedings{krause_et_al:DagSemProc.06111.2,
  author =	{Krause, Matthias and van Melkebeek, Dieter and Pudl\'{a}k, Pavel and Reischuk, R\"{u}diger},
  title =	{{06111 Executive Summary – Complexity of Boolean Functions}},
  booktitle =	{Complexity of Boolean Functions},
  pages =	{1--5},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2006},
  volume =	{6111},
  editor =	{Matthias Krause and Pavel Pudl\'{a}k and R\"{u}diger Reischuk and Dieter van Melkebeek},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.06111.2},
  URN =		{urn:nbn:de:0030-drops-8409},
  doi =		{10.4230/DagSemProc.06111.2},
  annote =	{Keywords: Boolean and quantum circuits, discrete problems, computational complexity, lower bounds, communication complexity, proof and query complexity, randomization, pseudo-randomness, derandomization, approximation, cryptography, computational learning}
}
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