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Documents authored by López-Ortiz, Alejandro

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López-Ortiz, Alejandro

Document
DOI: 10.4230/DagRep.6.3.1
Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 16101)

Authors: Alejandro Lopez-Ortiz, Ulrich Carsten Meyer, Markus E. Nebel, and Robert Sedgewick

Published in: Dagstuhl Reports, Volume 6, Issue 3 (2016)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 16101 "Data Structures and Advanced Models of Computation on Big Data". In today's computing environment vast amounts of data are processed, exchanged and analyzed. The manner in which information is stored profoundly influences the efficiency of these operations over the data. In spite of the maturity of the field many data structuring problems are still open, while new ones arise due to technological advances. The seminar covered both recent advances in the "classical" data structuring topics as well as new models of computation adapted to modern architectures, scientific studies that reveal the need for such models, applications where large data sets play a central role, modern computing platforms for very large data, and new data structures for large data in modern architectures. The extended abstracts included in this report contain both recent state of the art advances and lay the foundation for new directions within data structures research.
Cite as

Alejandro Lopez-Ortiz, Ulrich Carsten Meyer, Markus E. Nebel, and Robert Sedgewick. Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 16101). In Dagstuhl Reports, Volume 6, Issue 3, pp. 1-23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@Article{lopezortiz_et_al:DagRep.6.3.1,
  author =	{Lopez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Nebel, Markus E. and Sedgewick, Robert},
  title =	{{Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 16101)}},
  pages =	{1--23},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2016},
  volume =	{6},
  number =	{3},
  editor =	{Lopez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Nebel, Markus E. and Sedgewick, Robert},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.6.3.1},
  URN =		{urn:nbn:de:0030-drops-61457},
  doi =		{10.4230/DagRep.6.3.1},
  annote =	{Keywords: algorithms, big data, cloud services, data structures, external memory methods, information theory, large data sets, streaming, web-scale}
}
Document
DOI: 10.4230/LIPIcs.STACS.2015.636
Paid Exchanges are Worth the Price

Authors: Alejandro López-Ortiz, Marc P. Renault, and Adi Rosén

Published in: LIPIcs, Volume 30, 32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)

Abstract
We consider the list update problem as defined in the seminal work on competitive analysis by Sleator and Tarjan [12]. In this problem, a sequence of requests, consisting of items to access in a linked list, is given. After an item is accessed it can be moved to any position forward in the list at no cost (free exchange), and, at any time, any two adjacent items can be swapped at a cost of 1 (paid exchange). The cost to access an item is its current position in the list. The goal is to dynamically rearrange the list so as to minimize the total cost (accrued from accesses and exchanges) over the request sequence. We show a lower bound of 12/11 on the worst-case ratio between the performance of an (offline) optimal algorithm that can only perform free exchanges and that of an (offline) optimal algorithm that can perform both paid and free exchanges. This answers an outstanding question that has been open since 1996 [10].
Cite as

Alejandro López-Ortiz, Marc P. Renault, and Adi Rosén. Paid Exchanges are Worth the Price. In 32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 30, pp. 636-648, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{lopezortiz_et_al:LIPIcs.STACS.2015.636,
  author =	{L\'{o}pez-Ortiz, Alejandro and Renault, Marc P. and Ros\'{e}n, Adi},
  title =	{{Paid Exchanges are Worth the Price}},
  booktitle =	{32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)},
  pages =	{636--648},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-78-1},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{30},
  editor =	{Mayr, Ernst W. and Ollinger, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2015.636},
  URN =		{urn:nbn:de:0030-drops-49476},
  doi =		{10.4230/LIPIcs.STACS.2015.636},
  annote =	{Keywords: list update problem, online computation, online algorithms, competitive analysis, lower bounds}
}
Document
DOI: 10.4230/DagRep.4.2.129
Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 14091)

Authors: Alejandro López-Ortiz, Ulrich Carsten Meyer, and Robert Sedgewick

Published in: Dagstuhl Reports, Volume 4, Issue 2 (2014)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 14091 "Data Structures and Advanced Models of Computation on Big Data". In today's computing environment vast amounts of data are processed, exchanged and analyzed. The manner in which information is stored profoundly influences the efficiency of these operations over the data. In spite of the maturity of the field many data structuring problems are still open, while new ones arise due to technological advances. The seminar covered both recent advances in the "classical" data structuring topics as well as new models of computation adapted to modern architectures, scientific studies that reveal the need for such models, applications where large data sets play a central role, modern computing platforms for very large data, and new data structures for large data in modern architectures. The extended abstracts included in this report contain both recent state of the art advances and lay the foundation for new directions within data structures research.
Cite as

Alejandro López-Ortiz, Ulrich Carsten Meyer, and Robert Sedgewick. Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 14091). In Dagstuhl Reports, Volume 4, Issue 2, pp. 129-149, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@Article{lopezortiz_et_al:DagRep.4.2.129,
  author =	{L\'{o}pez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Sedgewick, Robert},
  title =	{{Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 14091)}},
  pages =	{129--149},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2014},
  volume =	{4},
  number =	{2},
  editor =	{L\'{o}pez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Sedgewick, Robert},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.4.2.129},
  URN =		{urn:nbn:de:0030-drops-45489},
  doi =		{10.4230/DagRep.4.2.129},
  annote =	{Keywords: data structures, big data, models of computation, I/O Model, sorting, quicksort, graph algorithms, hashing, compression, succinct data structures, trajectories, text search, GPU algorithms, MapReduce}
}
Document
DOI: 10.4230/LIPIcs.STACS.2014.174
Online Bin Packing with Advice

Authors: Joan Boyar, Shahin Kamali, Kim S. Larsen, and Alejandro López-Ortiz

Published in: LIPIcs, Volume 25, 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)

Abstract
We consider the online bin packing problem under the advice complexity model where the "online constraint" is relaxed and an algorithm receives partial information about the future requests. We provide tight upper and lower bounds for the amount of advice an algorithm needs to achieve an optimal packing. We also introduce an algorithm that, when provided with log(n)+o(log(n)) bits of advice, achieves a competitive ratio of 3/2 for the general problem. This algorithm is simple and is expected to find real-world applications. We introduce another algorithm that receives 2n+o(n) bits of advice and achieves a competitive ratio of 4/3+e. Finally, we provide a lower bound argument that implies that advice of linear size is required for an algorithm to achieve a competitive ratio better than 9/8.
Cite as

Joan Boyar, Shahin Kamali, Kim S. Larsen, and Alejandro López-Ortiz. Online Bin Packing with Advice. In 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014). Leibniz International Proceedings in Informatics (LIPIcs), Volume 25, pp. 174-186, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{boyar_et_al:LIPIcs.STACS.2014.174,
  author =	{Boyar, Joan and Kamali, Shahin and Larsen, Kim S. and L\'{o}pez-Ortiz, Alejandro},
  title =	{{Online Bin Packing with Advice}},
  booktitle =	{31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)},
  pages =	{174--186},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-65-1},
  ISSN =	{1868-8969},
  year =	{2014},
  volume =	{25},
  editor =	{Mayr, Ernst W. and Portier, Natacha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2014.174},
  URN =		{urn:nbn:de:0030-drops-44565},
  doi =		{10.4230/LIPIcs.STACS.2014.174},
  annote =	{Keywords: online algorithms, advice complexity, bin packing}
}
Document
DOI: 10.4230/LIPIcs.STACS.2011.380
A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times

Authors: Alejandro Lopez-Ortiz and Claude-Guy Quimper

Published in: LIPIcs, Volume 9, 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011)

Abstract
Consider the problem of scheduling a set of tasks of length p without preemption on $m$ identical machines with given release and deadline times. We present a new algorithm for computing the schedule with minimal completion times and makespan. The algorithm has time complexity O(min(1,p/m)n^2) which improves substantially over the best known algorithm with complexity O(mn^2).
Cite as

Alejandro Lopez-Ortiz and Claude-Guy Quimper. A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times. In 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011). Leibniz International Proceedings in Informatics (LIPIcs), Volume 9, pp. 380-391, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@InProceedings{lopezortiz_et_al:LIPIcs.STACS.2011.380,
  author =	{Lopez-Ortiz, Alejandro and Quimper, Claude-Guy},
  title =	{{A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times}},
  booktitle =	{28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011)},
  pages =	{380--391},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-25-5},
  ISSN =	{1868-8969},
  year =	{2011},
  volume =	{9},
  editor =	{Schwentick, Thomas and D\"{u}rr, Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2011.380},
  URN =		{urn:nbn:de:0030-drops-30282},
  doi =		{10.4230/LIPIcs.STACS.2011.380},
  annote =	{Keywords: Scheduling}
}
Document
DOI: 10.4230/DagSemProc.09171.1
09171 Abstracts Collection – Adaptive, Output Sensitive, Online and Parameterized Algorithms

Authors: Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier

Published in: Dagstuhl Seminar Proceedings, Volume 9171, Adaptive, Output Sensitive, Online and Parameterized Algorithms (2009)

Abstract
From 19.01. to 24.04.2009, the Dagstuhl Seminar 09171 ``Adaptive, Output Sensitive, Online and Parameterized Algorithms '' was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and 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 paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier. 09171 Abstracts Collection – Adaptive, Output Sensitive, Online and Parameterized Algorithms. In Adaptive, Output Sensitive, Online and Parameterized Algorithms. Dagstuhl Seminar Proceedings, Volume 9171, pp. 1-11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{barbay_et_al:DagSemProc.09171.1,
  author =	{Barbay, J\'{e}r\'{e}my and Klein, Rolf and L\'{o}pez-Ortiz, Alejandro and Niedermeier, Rolf},
  title =	{{09171 Abstracts Collection  – Adaptive, Output Sensitive, Online and Parameterized Algorithms}},
  booktitle =	{Adaptive, Output Sensitive, Online and Parameterized Algorithms},
  pages =	{1--11},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2009},
  volume =	{9171},
  editor =	{J\'{e}r\'{e}my Barbay and Rolf Klein and Alejandro Ortiz-L\'{o}pez and Rolf Niedermeier},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.09171.1},
  URN =		{urn:nbn:de:0030-drops-21228},
  doi =		{10.4230/DagSemProc.09171.1},
  annote =	{Keywords: Adaptive analysis, instance optimal algoritms, fixed parameter tractable, output sensitive algorithms}
}
Document
DOI: 10.4230/DagSemProc.09171.2
09171 Executive Summary – Adaptive, Output Sensitive, Online and Parameterized Algorithms

Authors: Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier

Published in: Dagstuhl Seminar Proceedings, Volume 9171, Adaptive, Output Sensitive, Online and Parameterized Algorithms (2009)

Abstract
Traditionally the analysis of algorithms measures the complexity of a problem or algorithm in terms of the worst-case behavior over all inputs of a given size. However, in certain cases an improved algorithm can be obtained by considering a finer partition of the input space. As this idea has been independently rediscovered in many areas, the workshop gathered participants from different fields in order to explore the impact and the limits of this technique, in the hope to spring new collaboration and to seed the unification of the technique.
Cite as

Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier. 09171 Executive Summary – Adaptive, Output Sensitive, Online and Parameterized Algorithms. In Adaptive, Output Sensitive, Online and Parameterized Algorithms. Dagstuhl Seminar Proceedings, Volume 9171, p. 1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{barbay_et_al:DagSemProc.09171.2,
  author =	{Barbay, J\'{e}r\'{e}my and Klein, Rolf and L\'{o}pez-Ortiz, Alejandro and Niedermeier, Rolf},
  title =	{{09171 Executive Summary – Adaptive, Output Sensitive, Online and Parameterized Algorithms}},
  booktitle =	{Adaptive, Output Sensitive, Online and Parameterized Algorithms},
  pages =	{1--1},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2009},
  volume =	{9171},
  editor =	{J\'{e}r\'{e}my Barbay and Rolf Klein and Alejandro Ortiz-L\'{o}pez and Rolf Niedermeier},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.09171.2},
  URN =		{urn:nbn:de:0030-drops-21207},
  doi =		{10.4230/DagSemProc.09171.2},
  annote =	{Keywords: Adaptive analysis, instance optimal algorithms, fixed parameter tractable, output sensitive algorithms}
}
Document
DOI: 10.4230/DagSemProc.08081.3
Optimal Speedup on a Low-Degree Multi-Core Parallel Architecture (LoPRAM)

Authors: Alejandro Lopez-Ortiz, Reza Dorrigiv, and Alejandro Salinger

Published in: Dagstuhl Seminar Proceedings, Volume 8081, Data Structures (2008)

Abstract
We propose a new model with small degreee of parallelism that reflects current and future multicore architectures in practice. The model is based on the PRAM architecture and hence it inherits many of its interesting theoretical properties. The key observations and differences are that the degree of parallelism (i.e. number of processors or cores) is bounded by O(log n), the synchronization model is looser and the use of parallelism is at a higher level unless explicitly specified otherwise. Surprisingly, these three rather minor variants result in a model in which obtaining work optimal algorithms is significantly easier than for the PRAM. The new model is called Low-degree PRAM or LoPRAM for short. Lastly we observe that there are thresholds in complexity of programming at p=O(log n) and p=O(sqrt(n)) and provide references for specific problems for which this threshold has been formally proven.
Cite as

Alejandro Lopez-Ortiz, Reza Dorrigiv, and Alejandro Salinger. Optimal Speedup on a Low-Degree Multi-Core Parallel Architecture (LoPRAM). In Data Structures. Dagstuhl Seminar Proceedings, Volume 8081, pp. 1-13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{lopezortiz_et_al:DagSemProc.08081.3,
  author =	{Lopez-Ortiz, Alejandro and Dorrigiv, Reza and Salinger, Alejandro},
  title =	{{Optimal Speedup on a Low-Degree Multi-Core Parallel Architecture (LoPRAM)}},
  booktitle =	{Data Structures},
  pages =	{1--13},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8081},
  editor =	{Lars Arge and Robert Sedgewick and Raimund Seidel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.08081.3},
  URN =		{urn:nbn:de:0030-drops-15315},
  doi =		{10.4230/DagSemProc.08081.3},
  annote =	{Keywords: PRAM, multicore architectures, parallelism, algorithms, dynamic programming, divide and conquer}
}
Document
DOI: 10.4230/DagSemProc.06421.1
06421 Abstracts Collection – Robot Navigation

Authors: Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz

Published in: Dagstuhl Seminar Proceedings, Volume 6421, Robot Navigation (2007)

Abstract
From 15.10.06 to 20.10.06, the Dagstuhl Seminar 06421 ``Robot Navigation''generate automatically was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and 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 paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz. 06421 Abstracts Collection – Robot Navigation. In Robot Navigation. Dagstuhl Seminar Proceedings, Volume 6421, pp. 1-12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)

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@InProceedings{fekete_et_al:DagSemProc.06421.1,
  author =	{Fekete, S\'{a}ndor and Fleischer, Rudolf and Klein, Rolf and Lopez-Ortiz, Alejandro},
  title =	{{06421 Abstracts Collection – Robot Navigation}},
  booktitle =	{Robot Navigation},
  pages =	{1--12},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6421},
  editor =	{S\'{a}ndor Fekete and Rudolf Fleischer and Rolf Klein and Alejandro Lopez-Ortiz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.06421.1},
  URN =		{urn:nbn:de:0030-drops-8890},
  doi =		{10.4230/DagSemProc.06421.1},
  annote =	{Keywords: Motion planning, robotics, computational geometry, online algorithms}
}
Document
DOI: 10.4230/DagSemProc.06421.2
06421 Executive Summary – Robot Navigation

Authors: Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz

Published in: Dagstuhl Seminar Proceedings, Volume 6421, Robot Navigation (2007)

Abstract
For quite a number of years, researchers from various fields have studied problems motivated by Robot Navigation. People in Online Algorithms have developed strategies that can deal with the inherent lack of information an autonomous robot encounters, as it sets out to perform a task in an unknown environment. Computational Geometers have obtained many results on the efficient planning of collision-free motions, and on visibility problems. Scientists and engineers in Robotics have perfected real robots to an astounding degree. Economic household robots and artificial pets are now available; more complex robots are able to carry out difficult search-and-rescue and exploration missions. The goal of this seminar is to bring together researchers from robotics, computational geometry, and online algorithms, in order to exchange problems and ideas, and to jointly work towards solutions. The following questions seem crucial. Given the advanced level of technical development, what are the strategic planning problems researchers in robotics need to solve in the next decade? How can real environments and robots be modeled, so that planning problems become tractable by algorithmic methods, and solutions are still significant for applications? In particular, what can be assumed about perception and motion accuracy? We are planning for plenary sessions where members of all groups can present their problems and recent work. In addition, there will be plenty of time for discussions.
Cite as

Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz. 06421 Executive Summary – Robot Navigation. In Robot Navigation. Dagstuhl Seminar Proceedings, Volume 6421, pp. 1-2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)

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@InProceedings{fekete_et_al:DagSemProc.06421.2,
  author =	{Fekete, S\'{a}ndor and Fleischer, Rudolf and Klein, Rolf and Lopez-Ortiz, Alejandro},
  title =	{{06421 Executive Summary – Robot Navigation}},
  booktitle =	{Robot Navigation},
  pages =	{1--2},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6421},
  editor =	{S\'{a}ndor Fekete and Rudolf Fleischer and Rolf Klein and Alejandro Lopez-Ortiz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.06421.2},
  URN =		{urn:nbn:de:0030-drops-8720},
  doi =		{10.4230/DagSemProc.06421.2},
  annote =	{Keywords: Motion planning, robotics, computational geometry, online algorithms}
}
Document
DOI: 10.4230/DagSemProc.06421.4
Adaptive Analysis of On-line Algorithms

Authors: Reza Dorrigiv and Alejandro Lopez-Ortiz

Published in: Dagstuhl Seminar Proceedings, Volume 6421, Robot Navigation (2007)

Abstract
On-line algorithms are usually analyzed using competitive analysis, in which the performance of on-line algorithm on a sequence is normalized by the performance of the optimal on-line algorithm on that sequence. In this paper we introduce adaptive/cooperative analysis as an alternative general framework for the analysis of on-line algorithms. This model gives promising results when applied to two well known on-line problems, paging and list update. The idea is to normalize the performance of an on-line algorithm by a measure other than the performance of the on-line optimal algorithm OPT. We show that in many instances the perform of OPT on a sequence is a coarse approximation of the difficulty or complexity of a given input. Using a finer, more natural measure we can separate paging and list update algorithms which were otherwise undistinguishable under the classical model. This createas a performance hierarchy of algorithms which better reflects the intuitive relative strengths between them. Lastly, we show that, surprisingly, certain randomized algorithms which are superior to MTF in the classical model are not so in the adaptive case. This confirms that the ability of the on-line adaptive algorithm to ignore pathological worst cases can lead to algorithms that are more efficient in practice.
Cite as

Reza Dorrigiv and Alejandro Lopez-Ortiz. Adaptive Analysis of On-line Algorithms. In Robot Navigation. Dagstuhl Seminar Proceedings, Volume 6421, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)

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@InProceedings{dorrigiv_et_al:DagSemProc.06421.4,
  author =	{Dorrigiv, Reza and Lopez-Ortiz, Alejandro},
  title =	{{Adaptive Analysis of On-line Algorithms}},
  booktitle =	{Robot Navigation},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6421},
  editor =	{S\'{a}ndor Fekete and Rudolf Fleischer and Rolf Klein and Alejandro Lopez-Ortiz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.06421.4},
  URN =		{urn:nbn:de:0030-drops-8696},
  doi =		{10.4230/DagSemProc.06421.4},
  annote =	{Keywords: On-line algorithms, paging, adaptive/cooperative analysis}
}

Lopez-Ortiz, Alejandro

Document
DOI: 10.4230/DagRep.6.3.1
Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 16101)

Authors: Alejandro Lopez-Ortiz, Ulrich Carsten Meyer, Markus E. Nebel, and Robert Sedgewick

Published in: Dagstuhl Reports, Volume 6, Issue 3 (2016)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 16101 "Data Structures and Advanced Models of Computation on Big Data". In today's computing environment vast amounts of data are processed, exchanged and analyzed. The manner in which information is stored profoundly influences the efficiency of these operations over the data. In spite of the maturity of the field many data structuring problems are still open, while new ones arise due to technological advances. The seminar covered both recent advances in the "classical" data structuring topics as well as new models of computation adapted to modern architectures, scientific studies that reveal the need for such models, applications where large data sets play a central role, modern computing platforms for very large data, and new data structures for large data in modern architectures. The extended abstracts included in this report contain both recent state of the art advances and lay the foundation for new directions within data structures research.
Cite as

Alejandro Lopez-Ortiz, Ulrich Carsten Meyer, Markus E. Nebel, and Robert Sedgewick. Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 16101). In Dagstuhl Reports, Volume 6, Issue 3, pp. 1-23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@Article{lopezortiz_et_al:DagRep.6.3.1,
  author =	{Lopez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Nebel, Markus E. and Sedgewick, Robert},
  title =	{{Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 16101)}},
  pages =	{1--23},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2016},
  volume =	{6},
  number =	{3},
  editor =	{Lopez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Nebel, Markus E. and Sedgewick, Robert},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.6.3.1},
  URN =		{urn:nbn:de:0030-drops-61457},
  doi =		{10.4230/DagRep.6.3.1},
  annote =	{Keywords: algorithms, big data, cloud services, data structures, external memory methods, information theory, large data sets, streaming, web-scale}
}
Document
DOI: 10.4230/LIPIcs.STACS.2015.636
Paid Exchanges are Worth the Price

Authors: Alejandro López-Ortiz, Marc P. Renault, and Adi Rosén

Published in: LIPIcs, Volume 30, 32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)

Abstract
We consider the list update problem as defined in the seminal work on competitive analysis by Sleator and Tarjan [12]. In this problem, a sequence of requests, consisting of items to access in a linked list, is given. After an item is accessed it can be moved to any position forward in the list at no cost (free exchange), and, at any time, any two adjacent items can be swapped at a cost of 1 (paid exchange). The cost to access an item is its current position in the list. The goal is to dynamically rearrange the list so as to minimize the total cost (accrued from accesses and exchanges) over the request sequence. We show a lower bound of 12/11 on the worst-case ratio between the performance of an (offline) optimal algorithm that can only perform free exchanges and that of an (offline) optimal algorithm that can perform both paid and free exchanges. This answers an outstanding question that has been open since 1996 [10].
Cite as

Alejandro López-Ortiz, Marc P. Renault, and Adi Rosén. Paid Exchanges are Worth the Price. In 32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 30, pp. 636-648, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{lopezortiz_et_al:LIPIcs.STACS.2015.636,
  author =	{L\'{o}pez-Ortiz, Alejandro and Renault, Marc P. and Ros\'{e}n, Adi},
  title =	{{Paid Exchanges are Worth the Price}},
  booktitle =	{32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)},
  pages =	{636--648},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-78-1},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{30},
  editor =	{Mayr, Ernst W. and Ollinger, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2015.636},
  URN =		{urn:nbn:de:0030-drops-49476},
  doi =		{10.4230/LIPIcs.STACS.2015.636},
  annote =	{Keywords: list update problem, online computation, online algorithms, competitive analysis, lower bounds}
}
Document
DOI: 10.4230/DagRep.4.2.129
Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 14091)

Authors: Alejandro López-Ortiz, Ulrich Carsten Meyer, and Robert Sedgewick

Published in: Dagstuhl Reports, Volume 4, Issue 2 (2014)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 14091 "Data Structures and Advanced Models of Computation on Big Data". In today's computing environment vast amounts of data are processed, exchanged and analyzed. The manner in which information is stored profoundly influences the efficiency of these operations over the data. In spite of the maturity of the field many data structuring problems are still open, while new ones arise due to technological advances. The seminar covered both recent advances in the "classical" data structuring topics as well as new models of computation adapted to modern architectures, scientific studies that reveal the need for such models, applications where large data sets play a central role, modern computing platforms for very large data, and new data structures for large data in modern architectures. The extended abstracts included in this report contain both recent state of the art advances and lay the foundation for new directions within data structures research.
Cite as

Alejandro López-Ortiz, Ulrich Carsten Meyer, and Robert Sedgewick. Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 14091). In Dagstuhl Reports, Volume 4, Issue 2, pp. 129-149, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@Article{lopezortiz_et_al:DagRep.4.2.129,
  author =	{L\'{o}pez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Sedgewick, Robert},
  title =	{{Data Structures and Advanced Models of Computation on Big Data (Dagstuhl Seminar 14091)}},
  pages =	{129--149},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2014},
  volume =	{4},
  number =	{2},
  editor =	{L\'{o}pez-Ortiz, Alejandro and Meyer, Ulrich Carsten and Sedgewick, Robert},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.4.2.129},
  URN =		{urn:nbn:de:0030-drops-45489},
  doi =		{10.4230/DagRep.4.2.129},
  annote =	{Keywords: data structures, big data, models of computation, I/O Model, sorting, quicksort, graph algorithms, hashing, compression, succinct data structures, trajectories, text search, GPU algorithms, MapReduce}
}
Document
DOI: 10.4230/LIPIcs.STACS.2014.174
Online Bin Packing with Advice

Authors: Joan Boyar, Shahin Kamali, Kim S. Larsen, and Alejandro López-Ortiz

Published in: LIPIcs, Volume 25, 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)

Abstract
We consider the online bin packing problem under the advice complexity model where the "online constraint" is relaxed and an algorithm receives partial information about the future requests. We provide tight upper and lower bounds for the amount of advice an algorithm needs to achieve an optimal packing. We also introduce an algorithm that, when provided with log(n)+o(log(n)) bits of advice, achieves a competitive ratio of 3/2 for the general problem. This algorithm is simple and is expected to find real-world applications. We introduce another algorithm that receives 2n+o(n) bits of advice and achieves a competitive ratio of 4/3+e. Finally, we provide a lower bound argument that implies that advice of linear size is required for an algorithm to achieve a competitive ratio better than 9/8.
Cite as

Joan Boyar, Shahin Kamali, Kim S. Larsen, and Alejandro López-Ortiz. Online Bin Packing with Advice. In 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014). Leibniz International Proceedings in Informatics (LIPIcs), Volume 25, pp. 174-186, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{boyar_et_al:LIPIcs.STACS.2014.174,
  author =	{Boyar, Joan and Kamali, Shahin and Larsen, Kim S. and L\'{o}pez-Ortiz, Alejandro},
  title =	{{Online Bin Packing with Advice}},
  booktitle =	{31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)},
  pages =	{174--186},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-65-1},
  ISSN =	{1868-8969},
  year =	{2014},
  volume =	{25},
  editor =	{Mayr, Ernst W. and Portier, Natacha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2014.174},
  URN =		{urn:nbn:de:0030-drops-44565},
  doi =		{10.4230/LIPIcs.STACS.2014.174},
  annote =	{Keywords: online algorithms, advice complexity, bin packing}
}
Document
DOI: 10.4230/LIPIcs.STACS.2011.380
A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times

Authors: Alejandro Lopez-Ortiz and Claude-Guy Quimper

Published in: LIPIcs, Volume 9, 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011)

Abstract
Consider the problem of scheduling a set of tasks of length p without preemption on $m$ identical machines with given release and deadline times. We present a new algorithm for computing the schedule with minimal completion times and makespan. The algorithm has time complexity O(min(1,p/m)n^2) which improves substantially over the best known algorithm with complexity O(mn^2).
Cite as

Alejandro Lopez-Ortiz and Claude-Guy Quimper. A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times. In 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011). Leibniz International Proceedings in Informatics (LIPIcs), Volume 9, pp. 380-391, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@InProceedings{lopezortiz_et_al:LIPIcs.STACS.2011.380,
  author =	{Lopez-Ortiz, Alejandro and Quimper, Claude-Guy},
  title =	{{A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times}},
  booktitle =	{28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011)},
  pages =	{380--391},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-25-5},
  ISSN =	{1868-8969},
  year =	{2011},
  volume =	{9},
  editor =	{Schwentick, Thomas and D\"{u}rr, Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2011.380},
  URN =		{urn:nbn:de:0030-drops-30282},
  doi =		{10.4230/LIPIcs.STACS.2011.380},
  annote =	{Keywords: Scheduling}
}
Document
DOI: 10.4230/DagSemProc.09171.1
09171 Abstracts Collection – Adaptive, Output Sensitive, Online and Parameterized Algorithms

Authors: Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier

Published in: Dagstuhl Seminar Proceedings, Volume 9171, Adaptive, Output Sensitive, Online and Parameterized Algorithms (2009)

Abstract
From 19.01. to 24.04.2009, the Dagstuhl Seminar 09171 ``Adaptive, Output Sensitive, Online and Parameterized Algorithms '' was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and 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 paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier. 09171 Abstracts Collection – Adaptive, Output Sensitive, Online and Parameterized Algorithms. In Adaptive, Output Sensitive, Online and Parameterized Algorithms. Dagstuhl Seminar Proceedings, Volume 9171, pp. 1-11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{barbay_et_al:DagSemProc.09171.1,
  author =	{Barbay, J\'{e}r\'{e}my and Klein, Rolf and L\'{o}pez-Ortiz, Alejandro and Niedermeier, Rolf},
  title =	{{09171 Abstracts Collection  – Adaptive, Output Sensitive, Online and Parameterized Algorithms}},
  booktitle =	{Adaptive, Output Sensitive, Online and Parameterized Algorithms},
  pages =	{1--11},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2009},
  volume =	{9171},
  editor =	{J\'{e}r\'{e}my Barbay and Rolf Klein and Alejandro Ortiz-L\'{o}pez and Rolf Niedermeier},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.09171.1},
  URN =		{urn:nbn:de:0030-drops-21228},
  doi =		{10.4230/DagSemProc.09171.1},
  annote =	{Keywords: Adaptive analysis, instance optimal algoritms, fixed parameter tractable, output sensitive algorithms}
}
Document
DOI: 10.4230/DagSemProc.09171.2
09171 Executive Summary – Adaptive, Output Sensitive, Online and Parameterized Algorithms

Authors: Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier

Published in: Dagstuhl Seminar Proceedings, Volume 9171, Adaptive, Output Sensitive, Online and Parameterized Algorithms (2009)

Abstract
Traditionally the analysis of algorithms measures the complexity of a problem or algorithm in terms of the worst-case behavior over all inputs of a given size. However, in certain cases an improved algorithm can be obtained by considering a finer partition of the input space. As this idea has been independently rediscovered in many areas, the workshop gathered participants from different fields in order to explore the impact and the limits of this technique, in the hope to spring new collaboration and to seed the unification of the technique.
Cite as

Jérémy Barbay, Rolf Klein, Alejandro López-Ortiz, and Rolf Niedermeier. 09171 Executive Summary – Adaptive, Output Sensitive, Online and Parameterized Algorithms. In Adaptive, Output Sensitive, Online and Parameterized Algorithms. Dagstuhl Seminar Proceedings, Volume 9171, p. 1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{barbay_et_al:DagSemProc.09171.2,
  author =	{Barbay, J\'{e}r\'{e}my and Klein, Rolf and L\'{o}pez-Ortiz, Alejandro and Niedermeier, Rolf},
  title =	{{09171 Executive Summary – Adaptive, Output Sensitive, Online and Parameterized Algorithms}},
  booktitle =	{Adaptive, Output Sensitive, Online and Parameterized Algorithms},
  pages =	{1--1},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2009},
  volume =	{9171},
  editor =	{J\'{e}r\'{e}my Barbay and Rolf Klein and Alejandro Ortiz-L\'{o}pez and Rolf Niedermeier},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.09171.2},
  URN =		{urn:nbn:de:0030-drops-21207},
  doi =		{10.4230/DagSemProc.09171.2},
  annote =	{Keywords: Adaptive analysis, instance optimal algorithms, fixed parameter tractable, output sensitive algorithms}
}
Document
DOI: 10.4230/DagSemProc.08081.3
Optimal Speedup on a Low-Degree Multi-Core Parallel Architecture (LoPRAM)

Authors: Alejandro Lopez-Ortiz, Reza Dorrigiv, and Alejandro Salinger

Published in: Dagstuhl Seminar Proceedings, Volume 8081, Data Structures (2008)

Abstract
We propose a new model with small degreee of parallelism that reflects current and future multicore architectures in practice. The model is based on the PRAM architecture and hence it inherits many of its interesting theoretical properties. The key observations and differences are that the degree of parallelism (i.e. number of processors or cores) is bounded by O(log n), the synchronization model is looser and the use of parallelism is at a higher level unless explicitly specified otherwise. Surprisingly, these three rather minor variants result in a model in which obtaining work optimal algorithms is significantly easier than for the PRAM. The new model is called Low-degree PRAM or LoPRAM for short. Lastly we observe that there are thresholds in complexity of programming at p=O(log n) and p=O(sqrt(n)) and provide references for specific problems for which this threshold has been formally proven.
Cite as

Alejandro Lopez-Ortiz, Reza Dorrigiv, and Alejandro Salinger. Optimal Speedup on a Low-Degree Multi-Core Parallel Architecture (LoPRAM). In Data Structures. Dagstuhl Seminar Proceedings, Volume 8081, pp. 1-13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{lopezortiz_et_al:DagSemProc.08081.3,
  author =	{Lopez-Ortiz, Alejandro and Dorrigiv, Reza and Salinger, Alejandro},
  title =	{{Optimal Speedup on a Low-Degree Multi-Core Parallel Architecture (LoPRAM)}},
  booktitle =	{Data Structures},
  pages =	{1--13},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2008},
  volume =	{8081},
  editor =	{Lars Arge and Robert Sedgewick and Raimund Seidel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.08081.3},
  URN =		{urn:nbn:de:0030-drops-15315},
  doi =		{10.4230/DagSemProc.08081.3},
  annote =	{Keywords: PRAM, multicore architectures, parallelism, algorithms, dynamic programming, divide and conquer}
}
Document
DOI: 10.4230/DagSemProc.06421.1
06421 Abstracts Collection – Robot Navigation

Authors: Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz

Published in: Dagstuhl Seminar Proceedings, Volume 6421, Robot Navigation (2007)

Abstract
From 15.10.06 to 20.10.06, the Dagstuhl Seminar 06421 ``Robot Navigation''generate automatically was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and 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 paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.
Cite as

Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz. 06421 Abstracts Collection – Robot Navigation. In Robot Navigation. Dagstuhl Seminar Proceedings, Volume 6421, pp. 1-12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)

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@InProceedings{fekete_et_al:DagSemProc.06421.1,
  author =	{Fekete, S\'{a}ndor and Fleischer, Rudolf and Klein, Rolf and Lopez-Ortiz, Alejandro},
  title =	{{06421 Abstracts Collection – Robot Navigation}},
  booktitle =	{Robot Navigation},
  pages =	{1--12},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6421},
  editor =	{S\'{a}ndor Fekete and Rudolf Fleischer and Rolf Klein and Alejandro Lopez-Ortiz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.06421.1},
  URN =		{urn:nbn:de:0030-drops-8890},
  doi =		{10.4230/DagSemProc.06421.1},
  annote =	{Keywords: Motion planning, robotics, computational geometry, online algorithms}
}
Document
DOI: 10.4230/DagSemProc.06421.2
06421 Executive Summary – Robot Navigation

Authors: Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz

Published in: Dagstuhl Seminar Proceedings, Volume 6421, Robot Navigation (2007)

Abstract
For quite a number of years, researchers from various fields have studied problems motivated by Robot Navigation. People in Online Algorithms have developed strategies that can deal with the inherent lack of information an autonomous robot encounters, as it sets out to perform a task in an unknown environment. Computational Geometers have obtained many results on the efficient planning of collision-free motions, and on visibility problems. Scientists and engineers in Robotics have perfected real robots to an astounding degree. Economic household robots and artificial pets are now available; more complex robots are able to carry out difficult search-and-rescue and exploration missions. The goal of this seminar is to bring together researchers from robotics, computational geometry, and online algorithms, in order to exchange problems and ideas, and to jointly work towards solutions. The following questions seem crucial. Given the advanced level of technical development, what are the strategic planning problems researchers in robotics need to solve in the next decade? How can real environments and robots be modeled, so that planning problems become tractable by algorithmic methods, and solutions are still significant for applications? In particular, what can be assumed about perception and motion accuracy? We are planning for plenary sessions where members of all groups can present their problems and recent work. In addition, there will be plenty of time for discussions.
Cite as

Sándor Fekete, Rudolf Fleischer, Rolf Klein, and Alejandro Lopez-Ortiz. 06421 Executive Summary – Robot Navigation. In Robot Navigation. Dagstuhl Seminar Proceedings, Volume 6421, pp. 1-2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)

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@InProceedings{fekete_et_al:DagSemProc.06421.2,
  author =	{Fekete, S\'{a}ndor and Fleischer, Rudolf and Klein, Rolf and Lopez-Ortiz, Alejandro},
  title =	{{06421 Executive Summary – Robot Navigation}},
  booktitle =	{Robot Navigation},
  pages =	{1--2},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6421},
  editor =	{S\'{a}ndor Fekete and Rudolf Fleischer and Rolf Klein and Alejandro Lopez-Ortiz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.06421.2},
  URN =		{urn:nbn:de:0030-drops-8720},
  doi =		{10.4230/DagSemProc.06421.2},
  annote =	{Keywords: Motion planning, robotics, computational geometry, online algorithms}
}
Document
DOI: 10.4230/DagSemProc.06421.4
Adaptive Analysis of On-line Algorithms

Authors: Reza Dorrigiv and Alejandro Lopez-Ortiz

Published in: Dagstuhl Seminar Proceedings, Volume 6421, Robot Navigation (2007)

Abstract
On-line algorithms are usually analyzed using competitive analysis, in which the performance of on-line algorithm on a sequence is normalized by the performance of the optimal on-line algorithm on that sequence. In this paper we introduce adaptive/cooperative analysis as an alternative general framework for the analysis of on-line algorithms. This model gives promising results when applied to two well known on-line problems, paging and list update. The idea is to normalize the performance of an on-line algorithm by a measure other than the performance of the on-line optimal algorithm OPT. We show that in many instances the perform of OPT on a sequence is a coarse approximation of the difficulty or complexity of a given input. Using a finer, more natural measure we can separate paging and list update algorithms which were otherwise undistinguishable under the classical model. This createas a performance hierarchy of algorithms which better reflects the intuitive relative strengths between them. Lastly, we show that, surprisingly, certain randomized algorithms which are superior to MTF in the classical model are not so in the adaptive case. This confirms that the ability of the on-line adaptive algorithm to ignore pathological worst cases can lead to algorithms that are more efficient in practice.
Cite as

Reza Dorrigiv and Alejandro Lopez-Ortiz. Adaptive Analysis of On-line Algorithms. In Robot Navigation. Dagstuhl Seminar Proceedings, Volume 6421, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)

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@InProceedings{dorrigiv_et_al:DagSemProc.06421.4,
  author =	{Dorrigiv, Reza and Lopez-Ortiz, Alejandro},
  title =	{{Adaptive Analysis of On-line Algorithms}},
  booktitle =	{Robot Navigation},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6421},
  editor =	{S\'{a}ndor Fekete and Rudolf Fleischer and Rolf Klein and Alejandro Lopez-Ortiz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.06421.4},
  URN =		{urn:nbn:de:0030-drops-8696},
  doi =		{10.4230/DagSemProc.06421.4},
  annote =	{Keywords: On-line algorithms, paging, adaptive/cooperative analysis}
}
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