Reports de recerca
http://hdl.handle.net/2117/3094
Tue, 20 Aug 2019 20:43:21 GMT2019-08-20T20:43:21ZA hybrid evolutionary algorithm based on solution merging for the longest arc-preserving common subsequence problem
http://hdl.handle.net/2117/129102
A hybrid evolutionary algorithm based on solution merging for the longest arc-preserving common subsequence problem
Blum, Christian; Blesa Aguilera, Maria Josep
The longest arc-preserving common subsequence problem is an NP-hard combinatorial optimization problem from the field of computational biology. This problem finds applications, in particular, in the comparison of arc-annotated Ribonucleic acid (RNA) sequences. In this work we propose a simple, hybrid evolutionary algorithm to tackle this problem. The most important feature of this algorithm concerns a crossover operator based on solution merging. In solution merging, two or more solutions to the problem are merged, and an exact technique is used to find the best solution within this union.
It is experimentally shown that the proposed algorithm outperforms a heuristic from the literature.
Thu, 14 Feb 2019 10:35:21 GMThttp://hdl.handle.net/2117/1291022019-02-14T10:35:21ZBlum, ChristianBlesa Aguilera, Maria JosepThe longest arc-preserving common subsequence problem is an NP-hard combinatorial optimization problem from the field of computational biology. This problem finds applications, in particular, in the comparison of arc-annotated Ribonucleic acid (RNA) sequences. In this work we propose a simple, hybrid evolutionary algorithm to tackle this problem. The most important feature of this algorithm concerns a crossover operator based on solution merging. In solution merging, two or more solutions to the problem are merged, and an exact technique is used to find the best solution within this union.
It is experimentally shown that the proposed algorithm outperforms a heuristic from the literature.Refinement by browsing: an alternative to thumbnails
http://hdl.handle.net/2117/124919
Refinement by browsing: an alternative to thumbnails
Gabarró Vallès, Joaquim; Vallejo, Isabel; Xhafa Xhafa, Fatos; Stewart, Alan; Clint, Maurice
Thumbnails are widely used in image retrieval and browsing systems. The use of such images compacts information. However, in situations where there are a large number of images on a server site, the use of thumbnails may still result in unacceptable response times when a user has access to a limited bandwidth. In this paper a refinement technique is proposed as an alternative to using thumbnails. The technique allows a user to identify the contents of an image early in its transmission. An efficient means of constructing a chain of image refinements of increasing quality to a given image is presented. Approximation chains can be employed either statically or dynamically. In the first case the level of detail is driven by the user; in the second case the level of detail is driven by a bandwidth aware server. Thus the proposed approach has application in grid and web computing.
Thu, 22 Nov 2018 12:25:43 GMThttp://hdl.handle.net/2117/1249192018-11-22T12:25:43ZGabarró Vallès, JoaquimVallejo, IsabelXhafa Xhafa, FatosStewart, AlanClint, MauriceThumbnails are widely used in image retrieval and browsing systems. The use of such images compacts information. However, in situations where there are a large number of images on a server site, the use of thumbnails may still result in unacceptable response times when a user has access to a limited bandwidth. In this paper a refinement technique is proposed as an alternative to using thumbnails. The technique allows a user to identify the contents of an image early in its transmission. An efficient means of constructing a chain of image refinements of increasing quality to a given image is presented. Approximation chains can be employed either statically or dynamically. In the first case the level of detail is driven by the user; in the second case the level of detail is driven by a bandwidth aware server. Thus the proposed approach has application in grid and web computing.On Berners-Lee computer, hints on navigability semantics and lack of referential integrity
http://hdl.handle.net/2117/124870
On Berners-Lee computer, hints on navigability semantics and lack of referential integrity
Gabarró Vallès, Joaquim; Vallejo, Isabel; Xhafa Xhafa, Fatos
In this paper we deal with semantics issues related to the stability, navigability and extensibility of web applications. To this end, we define a web application as a deterministic labelled transition system in which states are the html pages and transitions are urls. This definition allows us, on the one hand, to characterize the temporal evolution of a web application and, on the other, to classify web applications into several types according to how the information is spread over the web application. This last classification captures interesting semantic properties related to the navigability and web application extensibility. We use partial orders to define and characterize web applications extensibility as web program refinements in a way that preserve navigability and improve the information reached through browsing. We apply these ideas to construct a simple web application, namely, a small virtual museum based on approximations of three original paintings. Despite of being very simple, this example evidences the need for the semantic properties while designing the web application in order to assure navigability and obtaining better information while browsing. Based on the extensibility characterization, we were able to extend the virtual museum with different paintings approximations while preserving navigability properties as well as browsing of paintings' approximations of increased quality resolution. Finally, based on our model for web applications we formally define the web program refinements through partial orders.
Thu, 22 Nov 2018 07:18:29 GMThttp://hdl.handle.net/2117/1248702018-11-22T07:18:29ZGabarró Vallès, JoaquimVallejo, IsabelXhafa Xhafa, FatosIn this paper we deal with semantics issues related to the stability, navigability and extensibility of web applications. To this end, we define a web application as a deterministic labelled transition system in which states are the html pages and transitions are urls. This definition allows us, on the one hand, to characterize the temporal evolution of a web application and, on the other, to classify web applications into several types according to how the information is spread over the web application. This last classification captures interesting semantic properties related to the navigability and web application extensibility. We use partial orders to define and characterize web applications extensibility as web program refinements in a way that preserve navigability and improve the information reached through browsing. We apply these ideas to construct a simple web application, namely, a small virtual museum based on approximations of three original paintings. Despite of being very simple, this example evidences the need for the semantic properties while designing the web application in order to assure navigability and obtaining better information while browsing. Based on the extensibility characterization, we were able to extend the virtual museum with different paintings approximations while preserving navigability properties as well as browsing of paintings' approximations of increased quality resolution. Finally, based on our model for web applications we formally define the web program refinements through partial orders.A skeleton for the Tabu search metaheuristic with applications to problems in software engineering
http://hdl.handle.net/2117/124869
A skeleton for the Tabu search metaheuristic with applications to problems in software engineering
Blesa Aguilera, Maria Josep; Xhafa Xhafa, Fatos
We present a C++ implementation of a skeleton for Tabu Search method. Tabu Search method is a well-known meta-heuristic that has proved successful for sub-optimally solving hard combinatorial optimization problems. Recently there is an increasing interest in the application of meta-heuristics, such as Tabu Search, to problems in software engineering
Thu, 22 Nov 2018 07:06:33 GMThttp://hdl.handle.net/2117/1248692018-11-22T07:06:33ZBlesa Aguilera, Maria JosepXhafa Xhafa, FatosWe present a C++ implementation of a skeleton for Tabu Search method. Tabu Search method is a well-known meta-heuristic that has proved successful for sub-optimally solving hard combinatorial optimization problems. Recently there is an increasing interest in the application of meta-heuristics, such as Tabu Search, to problems in software engineeringNetwork creation games: structure vs anarchy
http://hdl.handle.net/2117/114967
Network creation games: structure vs anarchy
Álvarez Faura, M. del Carme; Messegué Buisan, Arnau
We study Nash equilibria and the price of anarchy in the classical model of Network Creation Games introduced by Fabrikant et al. In this model every agent (node) buys links at a prefixed price a > 0 in order to get connected to the network formed by all the n agents. In this setting, the reformulated tree conjecture states that for a > n, every Nash equilibrium network is a tree. Since it was shown that the price of anarchy for trees is constant, if the tree conjecture were true, then the price of anarchy would be constant for a > n. Moreover, Demaine et al. conjectured that the price of anarchy for this model is constant.
Up to now the last conjecture has been proven in (i) the lower range, for a = O(n1-o¿) with o¿ = 1 and (ii) in the upper range, for a > 65n. In
¿log n
contrast, the best upper bound known for the price of anarchy for the
remaining range is 2O(vlog n).
In this paper we give new insights into the structure of the Nash equilibria for different ranges of a and we enlarge the range for which the price of anarchy is constant. Regarding the upper range, we prove that every Nash equilibrium is a tree for a > 17n and that the price of anarchy is constant even for a > 9n. In the lower range, we show that any Nash equilibrium for a < n/C with C > 4, induces an o¿-distance-almost- uniform graph.
Fri, 09 Mar 2018 08:25:09 GMThttp://hdl.handle.net/2117/1149672018-03-09T08:25:09ZÁlvarez Faura, M. del CarmeMessegué Buisan, ArnauWe study Nash equilibria and the price of anarchy in the classical model of Network Creation Games introduced by Fabrikant et al. In this model every agent (node) buys links at a prefixed price a > 0 in order to get connected to the network formed by all the n agents. In this setting, the reformulated tree conjecture states that for a > n, every Nash equilibrium network is a tree. Since it was shown that the price of anarchy for trees is constant, if the tree conjecture were true, then the price of anarchy would be constant for a > n. Moreover, Demaine et al. conjectured that the price of anarchy for this model is constant.
Up to now the last conjecture has been proven in (i) the lower range, for a = O(n1-o¿) with o¿ = 1 and (ii) in the upper range, for a > 65n. In
¿log n
contrast, the best upper bound known for the price of anarchy for the
remaining range is 2O(vlog n).
In this paper we give new insights into the structure of the Nash equilibria for different ranges of a and we enlarge the range for which the price of anarchy is constant. Regarding the upper range, we prove that every Nash equilibrium is a tree for a > 17n and that the price of anarchy is constant even for a > 9n. In the lower range, we show that any Nash equilibrium for a < n/C with C > 4, induces an o¿-distance-almost- uniform graph.Examples of CF-bi-inmune and CF-levelable sets in LOGSPACE
http://hdl.handle.net/2117/110922
Examples of CF-bi-inmune and CF-levelable sets in LOGSPACE
Balcázar Navarro, José Luis; Díaz Cort, Josep; Gabarró Vallès, Joaquim
We find sets in the class LOGSPACE (on-line) that do not have good respectively approximations by context-free languages. For that we introduce the languages CF-bi-inmune and CF-levelable. We prove the results by defining directectly the sets and obtaining the properties via pumping arguments.; Trobem conjunts en la classe LOGSPACE (on-line) que no tenen bones respectivament òptimes aproximacions per llenguatges incontextuals. Per això introduïm els llenguatges CF-bi-inmune i CF-nivellable. Demostrem els resultats directament, definim els llenguatges i demostrem les propietats mitjançant el lema d'iteracció
Mon, 20 Nov 2017 14:52:27 GMThttp://hdl.handle.net/2117/1109222017-11-20T14:52:27ZBalcázar Navarro, José LuisDíaz Cort, JosepGabarró Vallès, JoaquimWe find sets in the class LOGSPACE (on-line) that do not have good respectively approximations by context-free languages. For that we introduce the languages CF-bi-inmune and CF-levelable. We prove the results by defining directectly the sets and obtaining the properties via pumping arguments.
Trobem conjunts en la classe LOGSPACE (on-line) que no tenen bones respectivament òptimes aproximacions per llenguatges incontextuals. Per això introduïm els llenguatges CF-bi-inmune i CF-nivellable. Demostrem els resultats directament, definim els llenguatges i demostrem les propietats mitjançant el lema d'iteraccióComplements des facteurs gauches de mots infinis et ambiguité : quelques exemples
http://hdl.handle.net/2117/110916
Complements des facteurs gauches de mots infinis et ambiguité : quelques exemples
Autebert, Jean-Michel; Gabarró Vallès, Joaquim
On se propose d'utiliser la méthode que P. Flajolet a décrit pour prouver l'ambiguité du langage de Goldstine [5], afin de prouver l'ambiguité d'une série de langages du même type. Ces langages sont tous des complémentaires des facteur gauches d'un mot infini.; Ens proposem utilitzar el mètode que P. Flajolet ha emprat per provar l'ambigüitat del llenguatge de Goldstine. Volem demostrar l'ambigüitat d'una sèrie de llenguatges del mateix tipus. Tots aquests llenguatges són complements de factors esquerres d'un mot infinit; We use a method given by P. Flajolet to prove the ambiguity of Goldstine language. With this technique we prove the ambiguity of some type of languages. Thse languages are all complements of left factors of infinite words.
Mon, 20 Nov 2017 11:02:07 GMThttp://hdl.handle.net/2117/1109162017-11-20T11:02:07ZAutebert, Jean-MichelGabarró Vallès, JoaquimOn se propose d'utiliser la méthode que P. Flajolet a décrit pour prouver l'ambiguité du langage de Goldstine [5], afin de prouver l'ambiguité d'une série de langages du même type. Ces langages sont tous des complémentaires des facteur gauches d'un mot infini.
Ens proposem utilitzar el mètode que P. Flajolet ha emprat per provar l'ambigüitat del llenguatge de Goldstine. Volem demostrar l'ambigüitat d'una sèrie de llenguatges del mateix tipus. Tots aquests llenguatges són complements de factors esquerres d'un mot infinit
We use a method given by P. Flajolet to prove the ambiguity of Goldstine language. With this technique we prove the ambiguity of some type of languages. Thse languages are all complements of left factors of infinite words.Connections among non uniform models for problems requiring high amount of resources
http://hdl.handle.net/2117/110914
Connections among non uniform models for problems requiring high amount of resources
Balcázar Navarro, José Luis; Gabarró Vallès, Joaquim
We characterize in terms of oracle Turing machines the classes defined by exponential lower bounds on some nonuniform complexity measures. After, we use the same methods to give a new characterization of classes defined by polynomial and polylog upper bounds, obtaining an unified approach to deal with upper and lower bounds. The measures are the initial index, the context-free cost, and the boolean circuits size. We interpret oir results by discussing a trade-off between oracle information and compued information for oracle Turing machines.; Caracteritzem per màquines de Turing amb oracles, classes de complexitat definides per fites interiors exponencials sobre mesures no uniformes. Els mateixos mètodes ens permeten d'obtenir caracteritzacions de classes definides fer fites superiors polinòmiques i "poly-log", unificant l'estudi de fites superiors amb el de fites inferiors. Les mesures són l'índex inicial, el cost incontextual i el cost booleà. Proposem una interpretació del resultat i discutim l'equilibri entre informació calculada i informació obtinguda de l'oracle.
Preliminary version
Mon, 20 Nov 2017 10:32:09 GMThttp://hdl.handle.net/2117/1109142017-11-20T10:32:09ZBalcázar Navarro, José LuisGabarró Vallès, JoaquimWe characterize in terms of oracle Turing machines the classes defined by exponential lower bounds on some nonuniform complexity measures. After, we use the same methods to give a new characterization of classes defined by polynomial and polylog upper bounds, obtaining an unified approach to deal with upper and lower bounds. The measures are the initial index, the context-free cost, and the boolean circuits size. We interpret oir results by discussing a trade-off between oracle information and compued information for oracle Turing machines.
Caracteritzem per màquines de Turing amb oracles, classes de complexitat definides per fites interiors exponencials sobre mesures no uniformes. Els mateixos mètodes ens permeten d'obtenir caracteritzacions de classes definides fer fites superiors polinòmiques i "poly-log", unificant l'estudi de fites superiors amb el de fites inferiors. Les mesures són l'índex inicial, el cost incontextual i el cost booleà. Proposem una interpretació del resultat i discutim l'equilibri entre informació calculada i informació obtinguda de l'oracle.On some "non uniform" complexity measures
http://hdl.handle.net/2117/110729
On some "non uniform" complexity measures
Balcázar Navarro, José Luis; Díaz Cort, Josep; Gabarró Vallès, Joaquim
Non-uniform complexity measures origined in Automata and Formal Languages Theory are characterized in terms of well-known uniform complexity classes. The initial index of languages is introduced by means of several computational models. It is shown to be closely related to context-free cost, boolean circuits straight line programs, and Turing machines with sparse oracles and time or space bounds.
Thu, 16 Nov 2017 09:17:25 GMThttp://hdl.handle.net/2117/1107292017-11-16T09:17:25ZBalcázar Navarro, José LuisDíaz Cort, JosepGabarró Vallès, JoaquimNon-uniform complexity measures origined in Automata and Formal Languages Theory are characterized in terms of well-known uniform complexity classes. The initial index of languages is introduced by means of several computational models. It is shown to be closely related to context-free cost, boolean circuits straight line programs, and Turing machines with sparse oracles and time or space bounds.Dos problemas
http://hdl.handle.net/2117/110696
Dos problemas
Gabarró Vallès, Joaquim
Wed, 15 Nov 2017 15:48:00 GMThttp://hdl.handle.net/2117/1106962017-11-15T15:48:00ZGabarró Vallès, Joaquim