ALBCOM  Algorismia, Bioinformàtica, Complexitat i Mètodes Formals
http://hdl.handle.net/2117/3092
20160526T22:43:26Z

A review on DISC 2005, the 19th International Symposium on Distributed Computing
http://hdl.handle.net/2117/87343
A review on DISC 2005, the 19th International Symposium on Distributed Computing
Blesa Aguilera, Maria Josep; Georgiou, Chryssis
DISC is an international symposium on the theory, design, analysis, implementation and application of distributed systems and networks. The wellknown International Symposium on Distributed Computing is organized annually in cooperation with the European Association for Theoretical Computer Science (EATCS). This is a review on the 19th International Symposium on Distributed Computing, which took place in Kraków, Poland, on September 2629, 2005. The proceedings of DISC 2005 are published by Springer, as volume 3724 of the Lecture Notes in Computer Science (LNCS) series. The conference website can be found at www.mimuw.edu.pl/~disc2005.
20160526T08:10:28Z
Blesa Aguilera, Maria Josep
Georgiou, Chryssis
DISC is an international symposium on the theory, design, analysis, implementation and application of distributed systems and networks. The wellknown International Symposium on Distributed Computing is organized annually in cooperation with the European Association for Theoretical Computer Science (EATCS). This is a review on the 19th International Symposium on Distributed Computing, which took place in Kraków, Poland, on September 2629, 2005. The proceedings of DISC 2005 are published by Springer, as volume 3724 of the Lecture Notes in Computer Science (LNCS) series. The conference website can be found at www.mimuw.edu.pl/~disc2005.

An algebraic view of the relation between largest common subtrees and smallest common supertrees
http://hdl.handle.net/2117/87254
An algebraic view of the relation between largest common subtrees and smallest common supertrees
Rosselló, Francesc; Valiente Feruglio, Gabriel Alejandro
The relationship between two important problems in tree pattern matching, the largest common subtree and the smallest common supertree of two trees, is established by means of simple constructions, which allow one to obtain the largest common subtree from the smallest common supertree, and vice versa. These constructions are given for the problems of isomorphic, homeomorphic, topological, and minor embeddings. They can be implemented by a straightforward extension of any algorithm that solves one of the two problems, and the extension only takes time linear in the size of the trees.
20160524T07:04:02Z
Rosselló, Francesc
Valiente Feruglio, Gabriel Alejandro
The relationship between two important problems in tree pattern matching, the largest common subtree and the smallest common supertree of two trees, is established by means of simple constructions, which allow one to obtain the largest common subtree from the smallest common supertree, and vice versa. These constructions are given for the problems of isomorphic, homeomorphic, topological, and minor embeddings. They can be implemented by a straightforward extension of any algorithm that solves one of the two problems, and the extension only takes time linear in the size of the trees.

Incorporating negative information in process discovery
http://hdl.handle.net/2117/87175
Incorporating negative information in process discovery
Ponce de León, Hernán; Carmona Vargas, Josep; vanden Broucke, Seppe
The discovery of a formal process model from event logs describing real process executions is a challenging problem that has been studied from several angles. Most of the contributions consider the extraction of a model as a semisupervised problem where only positive information is available. In this paper we present a fresh look at process discovery where also negative information can be taken into account. This feature may be crucial for deriving process models which are not only simple, fitting and precise, but also good on generalizing the right behavior underlying an event log. The technique is based on numerical abstract domains and Satisfiability Modulo Theories (SMT), and can be combined with any process discovery technique. As an example, we show in detail how to supervise a recent technique that uses numerical abstract domains. Experiments performed in our prototype implementation show the effectiveness of the techniques and the ability to improve the results produced by selected discovery techniques.
20160519T07:46:54Z
Ponce de León, Hernán
Carmona Vargas, Josep
vanden Broucke, Seppe
The discovery of a formal process model from event logs describing real process executions is a challenging problem that has been studied from several angles. Most of the contributions consider the extraction of a model as a semisupervised problem where only positive information is available. In this paper we present a fresh look at process discovery where also negative information can be taken into account. This feature may be crucial for deriving process models which are not only simple, fitting and precise, but also good on generalizing the right behavior underlying an event log. The technique is based on numerical abstract domains and Satisfiability Modulo Theories (SMT), and can be combined with any process discovery technique. As an example, we show in detail how to supervise a recent technique that uses numerical abstract domains. Experiments performed in our prototype implementation show the effectiveness of the techniques and the ability to improve the results produced by selected discovery techniques.

Logbased simplification of process models
http://hdl.handle.net/2117/87035
Logbased simplification of process models
San Pedro Martín, Javier de; Carmona Vargas, Josep; Cortadella Fortuny, Jordi
The visualization of models is essential for userfriendly humanmachine interactions during Process Mining. A simple graphical representation contributes to give intuitive information about the behavior of a system. However, complex systems cannot always be represented with succinct models that can be easily visualized. Qualitypreserving model simplifications can be of paramount importance to alleviate the complexity of finding useful and attractive visualizations.
This paper presents a collection of logbased techniques to simplify process models. The techniques trade off visualfriendly properties with quality metrics related to logs, such as fitness and precision, to avoid degrading the resulting model. The algorithms, either cast as optimization problems or heuristically guided, find simplified versions of the initial process model, and can be applied in the final stage of the process mining lifecycle, between the discovery of a process model and the deployment to the final user. A tool has been developed and tested on large logs, producing simplified process models that are one order of magnitude smaller while keeping fitness and precision under reasonable margins.
20160513T08:52:34Z
San Pedro Martín, Javier de
Carmona Vargas, Josep
Cortadella Fortuny, Jordi
The visualization of models is essential for userfriendly humanmachine interactions during Process Mining. A simple graphical representation contributes to give intuitive information about the behavior of a system. However, complex systems cannot always be represented with succinct models that can be easily visualized. Qualitypreserving model simplifications can be of paramount importance to alleviate the complexity of finding useful and attractive visualizations.
This paper presents a collection of logbased techniques to simplify process models. The techniques trade off visualfriendly properties with quality metrics related to logs, such as fitness and precision, to avoid degrading the resulting model. The algorithms, either cast as optimization problems or heuristically guided, find simplified versions of the initial process model, and can be applied in the final stage of the process mining lifecycle, between the discovery of a process model and the deployment to the final user. A tool has been developed and tested on large logs, producing simplified process models that are one order of magnitude smaller while keeping fitness and precision under reasonable margins.

Minimal representations for majority games
http://hdl.handle.net/2117/86215
Minimal representations for majority games
Freixas Bosch, Josep; Molinero Albareda, Xavier; Roura Ferret, Salvador
This paper presents some new results about majority games. Isbell (1959) was the first to find a majority game without a minimum normalized representation; he needed 12 voters to construct such a game. Since then, it has been an open problem to find the minimum number of voters of a majority game without a minimum normalized representation. Our main new results are: 1. All majority games with less than 9 voters have a minimum representation. 2. For 9 voters there are 14 majority games without a minimum integer representation, but these games admit a minimal normalized integer representation. 3. For 10 voters exist majority games with neither a minimum integer representation nor a minimal normalized integer representation.
20160427T07:22:54Z
Freixas Bosch, Josep
Molinero Albareda, Xavier
Roura Ferret, Salvador
This paper presents some new results about majority games. Isbell (1959) was the first to find a majority game without a minimum normalized representation; he needed 12 voters to construct such a game. Since then, it has been an open problem to find the minimum number of voters of a majority game without a minimum normalized representation. Our main new results are: 1. All majority games with less than 9 voters have a minimum representation. 2. For 9 voters there are 14 majority games without a minimum integer representation, but these games admit a minimal normalized integer representation. 3. For 10 voters exist majority games with neither a minimum integer representation nor a minimal normalized integer representation.

On the complexity of exchanging
http://hdl.handle.net/2117/86068
On the complexity of exchanging
Molinero Albareda, Xavier; Olsen, Martin; Serna Iglesias, María José
We analyze the computational complexity of the problem of deciding whether, for a given simple game, there exists the possibility of rearranging the participants in a set of j given losing coalitions into a set of j winning coalitions. We also look at the problem of turning winning coalitions into losing coalitions. We analyze the problem when the simple game is represented by a list of wining, losing, minimal winning or maximal loosing coalitions.
20160421T13:57:53Z
Molinero Albareda, Xavier
Olsen, Martin
Serna Iglesias, María José
We analyze the computational complexity of the problem of deciding whether, for a given simple game, there exists the possibility of rearranging the participants in a set of j given losing coalitions into a set of j winning coalitions. We also look at the problem of turning winning coalitions into losing coalitions. We analyze the problem when the simple game is represented by a list of wining, losing, minimal winning or maximal loosing coalitions.

Areaefficient snoopyaware NoC design for highperformance chip multiprocessor systems
http://hdl.handle.net/2117/85389
Areaefficient snoopyaware NoC design for highperformance chip multiprocessor systems
Roca Pérez, Antoni; Hernández Gañán, Carlos; Lodde, Mario; Flich Cardo, José
Manycore CMP systems are expected to grow to tens or even hundreds of cores. In this paper we show that the effective codesign of both, the networkonchip and the coherence protocol, improves performance and power meanwhile total area resources remain bounded. We propose a snoopyaware networkonchip topology made of two meshoftree topologies. Reducing the complexity of the coherence protocol  and hence its resources  and moving this complexity to the network, leads to a global decrease in power consumption meanwhile area is barely affected. Benefits of our proposal are due to the highthroughput and low delay of the network, but also due to the simplicity of the coherence protocol. The proposed network and protocol minimizes communication amongst cores when compared to traditional solutions based either on 2Dmesh topologies or in directorybased protocols.
20160408T07:51:16Z
Roca Pérez, Antoni
Hernández Gañán, Carlos
Lodde, Mario
Flich Cardo, José
Manycore CMP systems are expected to grow to tens or even hundreds of cores. In this paper we show that the effective codesign of both, the networkonchip and the coherence protocol, improves performance and power meanwhile total area resources remain bounded. We propose a snoopyaware networkonchip topology made of two meshoftree topologies. Reducing the complexity of the coherence protocol  and hence its resources  and moving this complexity to the network, leads to a global decrease in power consumption meanwhile area is barely affected. Benefits of our proposal are due to the highthroughput and low delay of the network, but also due to the simplicity of the coherence protocol. The proposed network and protocol minimizes communication amongst cores when compared to traditional solutions based either on 2Dmesh topologies or in directorybased protocols.

Can frogs find large independent sets in a decentralized way? Yes they can!
http://hdl.handle.net/2117/85203
Can frogs find large independent sets in a decentralized way? Yes they can!
Blum, Christian; Blesa Aguilera, Maria Josep; Calvo, Borja
The problem of identifying a maximal independent (node) set in a given graph is a fundamental problem in distributed computing. It has numerous applications, for example, in wireless networks in the context of facility location and backbone formation. In this paper we study the ability of a bioinspired, distributed algorithm, initially proposed for graph coloring, to generate large independent sets. The inspiration of the considered algorithm stems from the selfsynchronization capability of Japanese tree frogs. The experimental results confirm, indeed, that the algorithm has a strong tendency towards the generation of colorings in which the set of nodes assigned to the mostused color is rather large. Experimental results are compared to the ones of recent algorithms from the literature. Concerning solution quality, the results show that the froginspired algorithm has advantages especially for the application to rather sparse graphs. Concerning the computation round count, the algorithm has the advantage of converging within a reasonable number of iterations, regardless of the size and density of the considered graph.
20160405T12:13:40Z
Blum, Christian
Blesa Aguilera, Maria Josep
Calvo, Borja
The problem of identifying a maximal independent (node) set in a given graph is a fundamental problem in distributed computing. It has numerous applications, for example, in wireless networks in the context of facility location and backbone formation. In this paper we study the ability of a bioinspired, distributed algorithm, initially proposed for graph coloring, to generate large independent sets. The inspiration of the considered algorithm stems from the selfsynchronization capability of Japanese tree frogs. The experimental results confirm, indeed, that the algorithm has a strong tendency towards the generation of colorings in which the set of nodes assigned to the mostused color is rather large. Experimental results are compared to the ones of recent algorithms from the literature. Concerning solution quality, the results show that the froginspired algorithm has advantages especially for the application to rather sparse graphs. Concerning the computation round count, the algorithm has the advantage of converging within a reasonable number of iterations, regardless of the size and density of the considered graph.

Reactive clocks with variabilitytracking jitter
http://hdl.handle.net/2117/85192
Reactive clocks with variabilitytracking jitter
Cortadella Fortuny, Jordi; Lavagno, Luciano; López Muñoz, Pedro; Lupon Navazo, Marc; Moreno Vega, Alberto; Roca Pérez, Antoni; Sapatnekar, Sachin S.
The growing variability in nanoelectronic devices, due to uncertainties from the manufacturing process and environmental conditions (power supply, temperature, aging), requires increasing design guardbands, forcing circuits to work with conservative clock frequencies. Various schemes for clock generation based on ring oscillators and adaptive clocks have been proposed with the goal to mitigate the power and performance losses attributable to variability. However, there has been no systematic analysis to quantify the benefits of such schemes and no signoff method has been proposed for timing correctness. This paper presents and analyzes a Reactive Clocking scheme with VariabilityTracking Jitter (RClk) that uses variability as an opportunity to reduce power by continuously adjusting the clock frequency to the varying environmental conditions, and thus, reduces guardband margins significantly. Power can be reduced between 20% and 40% at isoperformance and performance can be boosted by similar amounts at isopower. Additionally, energy savings can be translated to substantial advantages in terms of reliability and thermal management. More importantly, the technology can be adopted with minimal modifications to conventional EDA flows.
© 2015 IEEE.Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20160405T11:41:46Z
Cortadella Fortuny, Jordi
Lavagno, Luciano
López Muñoz, Pedro
Lupon Navazo, Marc
Moreno Vega, Alberto
Roca Pérez, Antoni
Sapatnekar, Sachin S.
The growing variability in nanoelectronic devices, due to uncertainties from the manufacturing process and environmental conditions (power supply, temperature, aging), requires increasing design guardbands, forcing circuits to work with conservative clock frequencies. Various schemes for clock generation based on ring oscillators and adaptive clocks have been proposed with the goal to mitigate the power and performance losses attributable to variability. However, there has been no systematic analysis to quantify the benefits of such schemes and no signoff method has been proposed for timing correctness. This paper presents and analyzes a Reactive Clocking scheme with VariabilityTracking Jitter (RClk) that uses variability as an opportunity to reduce power by continuously adjusting the clock frequency to the varying environmental conditions, and thus, reduces guardband margins significantly. Power can be reduced between 20% and 40% at isoperformance and performance can be boosted by similar amounts at isopower. Additionally, energy savings can be translated to substantial advantages in terms of reliability and thermal management. More importantly, the technology can be adopted with minimal modifications to conventional EDA flows.

Clustering media items stemming from multiple social networks
http://hdl.handle.net/2117/84996
Clustering media items stemming from multiple social networks
Steiner, Thomas; Verborgh, Ruben; Gabarró Vallès, Joaquim; Mannens, Erik; Van de Walle, Rik
We have created and evaluated an algorithm capable of deduplicating and clustering exact and nearduplicate media items of type photo and video that get shared on multiple social networks in the context of events. This algorithm works in an entirely ad hoc manner without requiring any precalculation. When people attend events, they more and more share eventrelated media items publicly on social networks to let their social network contacts relive and witness the attended events. In the past, we have worked on methods to accumulate such public usergenerated multimedia content in order to summarize events visually, for example, in the form of media galleries or slideshows. In this paper, first, we introduce socialnetworkspecific reasons and challenges that cause nearduplicate media items. Second, we detail an algorithm for the task of deduplicating and clustering exact and nearduplicate media items stemming from multiple social networks. Finally, we evaluate the algorithm's strengths and weaknesses and thoroughly compare its performance with the stateoftheart feature detection algorithms SIFT, ASIFT and SURF and show that for the given use case it performs almost equally well accuracywise, but strongly outperforms speedwise.
20160331T14:07:07Z
Steiner, Thomas
Verborgh, Ruben
Gabarró Vallès, Joaquim
Mannens, Erik
Van de Walle, Rik
We have created and evaluated an algorithm capable of deduplicating and clustering exact and nearduplicate media items of type photo and video that get shared on multiple social networks in the context of events. This algorithm works in an entirely ad hoc manner without requiring any precalculation. When people attend events, they more and more share eventrelated media items publicly on social networks to let their social network contacts relive and witness the attended events. In the past, we have worked on methods to accumulate such public usergenerated multimedia content in order to summarize events visually, for example, in the form of media galleries or slideshows. In this paper, first, we introduce socialnetworkspecific reasons and challenges that cause nearduplicate media items. Second, we detail an algorithm for the task of deduplicating and clustering exact and nearduplicate media items stemming from multiple social networks. Finally, we evaluate the algorithm's strengths and weaknesses and thoroughly compare its performance with the stateoftheart feature detection algorithms SIFT, ASIFT and SURF and show that for the given use case it performs almost equally well accuracywise, but strongly outperforms speedwise.