3 Search Results for "Pagourtzis, Aris"


Document
Counting Computations with Formulae: Logical Characterisations of Counting Complexity Classes

Authors: Antonis Achilleos and Aggeliki Chalki

Published in: LIPIcs, Volume 272, 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)


Abstract
We present quantitative logics with two-step semantics based on the framework of quantitative logics introduced by Arenas et al. (2020) and the two-step semantics defined in the context of weighted logics by Gastin & Monmege (2018). We show that some of the fragments of our logics augmented with a least fixed point operator capture interesting classes of counting problems. Specifically, we answer an open question in the area of descriptive complexity of counting problems by providing logical characterisations of two subclasses of #P, namely SpanL and TotP, that play a significant role in the study of approximable counting problems. Moreover, we define logics that capture FPSPACE and SpanPSPACE, which are counting versions of PSPACE.

Cite as

Antonis Achilleos and Aggeliki Chalki. Counting Computations with Formulae: Logical Characterisations of Counting Complexity Classes. In 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 272, pp. 7:1-7:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


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@InProceedings{achilleos_et_al:LIPIcs.MFCS.2023.7,
  author =	{Achilleos, Antonis and Chalki, Aggeliki},
  title =	{{Counting Computations with Formulae: Logical Characterisations of Counting Complexity Classes}},
  booktitle =	{48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)},
  pages =	{7:1--7:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-292-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{272},
  editor =	{Leroux, J\'{e}r\^{o}me and Lombardy, Sylvain and Peleg, David},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2023.7},
  URN =		{urn:nbn:de:0030-drops-185412},
  doi =		{10.4230/LIPIcs.MFCS.2023.7},
  annote =	{Keywords: descriptive complexity, quantitative logics, counting problems, #P}
}
Document
Tight Bounds for Deterministic h-Shot Broadcast in Ad-Hoc Directed Radio Networks

Authors: Aris Pagourtzis and Tomasz Radzik

Published in: LIPIcs, Volume 117, 43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018)


Abstract
We consider the classical broadcast problem in ad-hoc (that is, unknown topology) directed radio networks with no collision detection, under the additional assumption that at most h transmissions (shots) are available per node. We focus on adaptive deterministic protocols for small values of h. We provide asymptotically matching lower and upper bounds for the cases h=2 and h=3. While for h=2 our bound is quadratic, similar to the bound obtained for oblivious protocols, for h=3 we prove a sub-quadratic bound of Theta(n^2 log log n / log n), where n is the number of nodes in the network. The latter is the first result showing an adaptive algorithm which is asymptotically faster than oblivious h-shot broadcast protocols, for which a tight quadratic bound is known for every constant h. Our upper bound for h=3 is constructive, making use of constructions of graphs with large girth. We also show an improved upper bound of O(n^(1+alpha/sqrt{h})) for h >= 4, where alpha is an absolute constant independent of h. Our upper bound for h >= 4 is non-constructive.

Cite as

Aris Pagourtzis and Tomasz Radzik. Tight Bounds for Deterministic h-Shot Broadcast in Ad-Hoc Directed Radio Networks. In 43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 117, pp. 80:1-80:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


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@InProceedings{pagourtzis_et_al:LIPIcs.MFCS.2018.80,
  author =	{Pagourtzis, Aris and Radzik, Tomasz},
  title =	{{Tight Bounds for Deterministic h-Shot Broadcast in Ad-Hoc Directed Radio Networks}},
  booktitle =	{43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018)},
  pages =	{80:1--80:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-086-6},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{117},
  editor =	{Potapov, Igor and Spirakis, Paul and Worrell, James},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2018.80},
  URN =		{urn:nbn:de:0030-drops-96629},
  doi =		{10.4230/LIPIcs.MFCS.2018.80},
  annote =	{Keywords: Ad-hoc radio networks, wireless networks, deterministic broadcast, adaptive protocols, limited transmissions}
}
Document
Periodic Metro Scheduling

Authors: Evangelos Bampas, Georgia Kaouri, Michael Lampis, and Aris Pagourtzis

Published in: OASIcs, Volume 5, 6th Workshop on Algorithmic Methods and Models for Optimization of Railways (ATMOS'06) (2006)


Abstract
We introduce the { extsc{Periodic Metro Sched-ul-ing}} ({ extsc{PMS}}) problem, which aims in generating a periodic timetable for a given set of routes and a given time period, in such a way that the minimum time distance between any two successive trains that pass from the same point of the network is maximized. This can be particularly useful in cases where trains use the same rail segment quite often, as happens in metropolitan rail networks. We present exact algorithms for ({ extsc{PMS}}) in chain and spider networks, and constant ratio approximation algorithms for ring networks and for a special class of tree networks. Some of our algorithms are based on a reduction to the { extsc{Path Coloring}} problem, while others rely on techniques specially designed for the new problem.

Cite as

Evangelos Bampas, Georgia Kaouri, Michael Lampis, and Aris Pagourtzis. Periodic Metro Scheduling. In 6th Workshop on Algorithmic Methods and Models for Optimization of Railways (ATMOS'06). Open Access Series in Informatics (OASIcs), Volume 5, pp. 1-15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2006)


Copy BibTex To Clipboard

@InProceedings{bampas_et_al:OASIcs.ATMOS.2006.684,
  author =	{Bampas, Evangelos and Kaouri, Georgia and Lampis, Michael and Pagourtzis, Aris},
  title =	{{Periodic Metro Scheduling}},
  booktitle =	{6th Workshop on Algorithmic Methods and Models for Optimization of Railways (ATMOS'06)},
  pages =	{1--15},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-01-9},
  ISSN =	{2190-6807},
  year =	{2006},
  volume =	{5},
  editor =	{Jacob, Riko and M\"{u}ller-Hannemann, Matthias},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2006.684},
  URN =		{urn:nbn:de:0030-drops-6841},
  doi =		{10.4230/OASIcs.ATMOS.2006.684},
  annote =	{Keywords: Train scheduling, path coloring, delay-tolerant scheduling, periodic timetabling}
}
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