Articles de revista
http://hdl.handle.net/2117/3918
Mon, 08 Feb 2016 17:34:01 GMT2016-02-08T17:34:01ZDisturbance decoupling problem for switched linear systems. A geometric approach
http://hdl.handle.net/2117/82288
Disturbance decoupling problem for switched linear systems. A geometric approach
García Planas, María Isabel
In this paper disturbance decoupling problem for switched linear systems is formulated under a geometrical
point of view. Necessary and sufficient conditions for the problem with standardizable condition to be
solvable are given
Fri, 29 Jan 2016 12:57:45 GMThttp://hdl.handle.net/2117/822882016-01-29T12:57:45ZGarcía Planas, María IsabelIn this paper disturbance decoupling problem for switched linear systems is formulated under a geometrical
point of view. Necessary and sufficient conditions for the problem with standardizable condition to be
solvable are givenOverdetermined partial resolvent kernels for finite networks
http://hdl.handle.net/2117/82285
Overdetermined partial resolvent kernels for finite networks
Arauz Lombardia, Cristina; Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos
In [2], a study of the existence and uniqueness of solution of partial overdetermined boundary value problems for finite networks was performed. These problems involve Schrodinger operators and the novel feature is that no data are prescribed on part of the boundary, whereas both the values of the function and of its normal derivative are given on another part of the boundary. In the present work, we study the resolvent kernels associated with overdetermined partial boundary value problems on finite network and we express them in terms of the well-known Green operator and the Dirichlet-to-Robin map. Moreover, we analyze their main properties and we compute them in the case of a generalized cylinder. The obtained expression involve polynomials that can be seen as a generalization of Chebyshev polynomials, and indeed when the conductances along axes are constant the expressions for the overdetermined partial resolvent kernels are given in terms of second kind Chebyshev polynomials. (C) 2015 Elsevier Inc. All rights reserved.
Fri, 29 Jan 2016 12:49:33 GMThttp://hdl.handle.net/2117/822852016-01-29T12:49:33ZArauz Lombardia, CristinaCarmona Mejías, ÁngelesEncinas Bachiller, Andrés MarcosIn [2], a study of the existence and uniqueness of solution of partial overdetermined boundary value problems for finite networks was performed. These problems involve Schrodinger operators and the novel feature is that no data are prescribed on part of the boundary, whereas both the values of the function and of its normal derivative are given on another part of the boundary. In the present work, we study the resolvent kernels associated with overdetermined partial boundary value problems on finite network and we express them in terms of the well-known Green operator and the Dirichlet-to-Robin map. Moreover, we analyze their main properties and we compute them in the case of a generalized cylinder. The obtained expression involve polynomials that can be seen as a generalization of Chebyshev polynomials, and indeed when the conductances along axes are constant the expressions for the overdetermined partial resolvent kernels are given in terms of second kind Chebyshev polynomials. (C) 2015 Elsevier Inc. All rights reserved.Problem A-20: A rational sum
http://hdl.handle.net/2117/82241
Problem A-20: A rational sum
Díaz Barrero, José Luis; Gibergans Baguena, José
Thu, 28 Jan 2016 16:21:22 GMThttp://hdl.handle.net/2117/822412016-01-28T16:21:22ZDíaz Barrero, José LuisGibergans Baguena, JoséThe relation type of affine algebras and algebraic varieties
http://hdl.handle.net/2117/82051
The relation type of affine algebras and algebraic varieties
Planas Vilanova, Francesc d'Assís
We introduce the notion of relation type of an affine algebra and prove that it is well defined by using the Jacobi-Zariski exact sequence of Andre-Quillen homology. In particular, the relation type,is an invariant of an affine algebraic variety. Also as a consequence of the invariance, we show that in order to calculate the relation type of an ideal in a polynomial ring one can reduce the problem to trinomial ideals. When the relation type is at least two, the extreme equidimensional components play no role. This leads to the non-existence of affine algebras of embedding dimension three and relation type two. (C) 2015 Elsevier Inc. All rights reserved.
Tue, 26 Jan 2016 12:41:29 GMThttp://hdl.handle.net/2117/820512016-01-26T12:41:29ZPlanas Vilanova, Francesc d'AssísWe introduce the notion of relation type of an affine algebra and prove that it is well defined by using the Jacobi-Zariski exact sequence of Andre-Quillen homology. In particular, the relation type,is an invariant of an affine algebraic variety. Also as a consequence of the invariance, we show that in order to calculate the relation type of an ideal in a polynomial ring one can reduce the problem to trinomial ideals. When the relation type is at least two, the extreme equidimensional components play no role. This leads to the non-existence of affine algebras of embedding dimension three and relation type two. (C) 2015 Elsevier Inc. All rights reserved.Absolute order-of-magnitude reasoning applied to a social multi-criteria evaluation framework
http://hdl.handle.net/2117/82020
Absolute order-of-magnitude reasoning applied to a social multi-criteria evaluation framework
Afsordegan, Arayeh; Sánchez Soler, Monica; Agell Jané, Núria; Aguado Chao, Juan Carlos; Gamboa Jimenez, Gonzalo
A social multi-criteria evaluation framework for solving a real-case problem of selecting a wind farm location in the regions of Urgell and Conca de Barberá in Catalonia (northeast of Spain) is studied. This paper applies a qualitative multi-criteria decision analysis approach based on linguistic labels assessment able to address uncertainty and deal with different levels of precision. This method is based on qualitative reasoning as an artificial intelligence technique for assessing and ranking multi-attribute alternatives with linguistic labels in order to handle uncertainty. This method is suitable for problems in the social framework such as energy planning which require the construction of a dialogue process among many social actors with high level of complexity and uncertainty. The method is compared with an existing approach, which has been applied previously in the wind farm location problem. This approach, consisting of an outranking method, is based on Condorcet's original method. The results obtained by both approaches are analysed and their performance in the selection of the wind farm location is compared in aggregation procedures. Although results show that both methods conduct to similar alternatives rankings, the study highlights both their advantages and drawbacks.
This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Experimental & Theoretical Artificial Intelligence on 27.04.2015, available online: http://www.tandfonline.com/doi/10.1080/0952813X.2015.1024489
Tue, 26 Jan 2016 09:33:43 GMThttp://hdl.handle.net/2117/820202016-01-26T09:33:43ZAfsordegan, ArayehSánchez Soler, MonicaAgell Jané, NúriaAguado Chao, Juan CarlosGamboa Jimenez, GonzaloA social multi-criteria evaluation framework for solving a real-case problem of selecting a wind farm location in the regions of Urgell and Conca de Barberá in Catalonia (northeast of Spain) is studied. This paper applies a qualitative multi-criteria decision analysis approach based on linguistic labels assessment able to address uncertainty and deal with different levels of precision. This method is based on qualitative reasoning as an artificial intelligence technique for assessing and ranking multi-attribute alternatives with linguistic labels in order to handle uncertainty. This method is suitable for problems in the social framework such as energy planning which require the construction of a dialogue process among many social actors with high level of complexity and uncertainty. The method is compared with an existing approach, which has been applied previously in the wind farm location problem. This approach, consisting of an outranking method, is based on Condorcet's original method. The results obtained by both approaches are analysed and their performance in the selection of the wind farm location is compared in aggregation procedures. Although results show that both methods conduct to similar alternatives rankings, the study highlights both their advantages and drawbacks.Completion and decomposition of hypergraphs into dominating sets of graphs
http://hdl.handle.net/2117/81940
Completion and decomposition of hypergraphs into dominating sets of graphs
Martí Farré, Jaume; Mora Giné, Mercè; Ruiz Muñoz, José Luis
The collection of the vertex dominating sets of a graph defines a hypergraph on the set of vertices of the graph. However, there are hypergraphs H that are not the collection of the vertex dominating sets of any graph. This paper deals with the question of completing these hypergraphs H to the vertex dominating sets of some graphs G. We demonstrate that such graphs G exist and, in addition, we prove that these graphs define a poset whose minimal elements provide a decomposition of H. Moreover, we show that the hypergraph H is uniquely determined by the minimal elements of this poset. The computation of such minimal elements is also discussed in some cases.
Mon, 25 Jan 2016 09:39:08 GMThttp://hdl.handle.net/2117/819402016-01-25T09:39:08ZMartí Farré, JaumeMora Giné, MercèRuiz Muñoz, José LuisThe collection of the vertex dominating sets of a graph defines a hypergraph on the set of vertices of the graph. However, there are hypergraphs H that are not the collection of the vertex dominating sets of any graph. This paper deals with the question of completing these hypergraphs H to the vertex dominating sets of some graphs G. We demonstrate that such graphs G exist and, in addition, we prove that these graphs define a poset whose minimal elements provide a decomposition of H. Moreover, we show that the hypergraph H is uniquely determined by the minimal elements of this poset. The computation of such minimal elements is also discussed in some cases.Precompensated Second Order Repetitive Control of an Active Filter Under Varying Network Frequency
http://hdl.handle.net/2117/81931
Precompensated Second Order Repetitive Control of an Active Filter Under Varying Network Frequency
Ramos Fuentes, German A.; Costa Castelló, Ramon; Olm Miras, Josep Maria
Network frequency variations cause a dramatic performance decay in repetitive controller-based shunt active power filters. This problem may be solved by adapting the sampling period in order to keep the ratio between the network period and the sampling period at a constant value. However, these changes may yield closed-loop instability. The introduction of a precompensator that forces the plant to remain invariant despite sampling rate changes allows the use of standard LTI methods in control design and stability analysis as well. Moreover, in order to improve robustness in the face of network frequency estimation uncertainty and sampling time quantization, the regular repetitive controller is replaced by a high order one. Experimental results show the validity of the proposal.
Mon, 25 Jan 2016 08:59:15 GMThttp://hdl.handle.net/2117/819312016-01-25T08:59:15ZRamos Fuentes, German A.Costa Castelló, RamonOlm Miras, Josep MariaNetwork frequency variations cause a dramatic performance decay in repetitive controller-based shunt active power filters. This problem may be solved by adapting the sampling period in order to keep the ratio between the network period and the sampling period at a constant value. However, these changes may yield closed-loop instability. The introduction of a precompensator that forces the plant to remain invariant despite sampling rate changes allows the use of standard LTI methods in control design and stability analysis as well. Moreover, in order to improve robustness in the face of network frequency estimation uncertainty and sampling time quantization, the regular repetitive controller is replaced by a high order one. Experimental results show the validity of the proposal.A new multisymplectic unified formalism for second order classical field theories
http://hdl.handle.net/2117/81889
A new multisymplectic unified formalism for second order classical field theories
Prieto Martínez, Pedro Daniel; Román Roy, Narciso
We present a new multisymplectic framework for second-order classical field theories which is based on an extension of the unified LagrangianHamiltonian formalism to these kinds of systems. This model provides a straightforward and simple way to define the Poincare-Cartan form and clarifies the construction of the Legendre map (univocally obtained as a consequence of the constraint algorithm). Likewise, it removes the undesirable arbitrariness in the solutions to the field equations, which are analyzed in-depth, and written in terms of holonomic sections and multivector fields. Our treatment therefore completes previous attempt to achieve this aim. The formulation is applied to describing some physical examples; in particular, to giving another alternative multisymplectic description of the Korteweg-de Vries equation.
Fri, 22 Jan 2016 12:29:06 GMThttp://hdl.handle.net/2117/818892016-01-22T12:29:06ZPrieto Martínez, Pedro DanielRomán Roy, NarcisoWe present a new multisymplectic framework for second-order classical field theories which is based on an extension of the unified LagrangianHamiltonian formalism to these kinds of systems. This model provides a straightforward and simple way to define the Poincare-Cartan form and clarifies the construction of the Legendre map (univocally obtained as a consequence of the constraint algorithm). Likewise, it removes the undesirable arbitrariness in the solutions to the field equations, which are analyzed in-depth, and written in terms of holonomic sections and multivector fields. Our treatment therefore completes previous attempt to achieve this aim. The formulation is applied to describing some physical examples; in particular, to giving another alternative multisymplectic description of the Korteweg-de Vries equation.Connectivity and other invariants of generalized products of graphs
http://hdl.handle.net/2117/81804
Connectivity and other invariants of generalized products of graphs
López Masip, Susana Clara; Muntaner Batle, Francesc Antoni
Figueroa-Centeno et al. [4] introduced the following product of digraphs let D be a digraph and let G be a family of digraphs such that V (F) = V for every F¿G. Consider any function h:E(D)¿G. Then the product D¿hG is the digraph with vertex set V(D)×V and ((a,x),(b,y))¿E(D¿hG) if and only if (a,b)¿E(D) and (x,y)¿E(h(a,b)). In this paper, we deal with the undirected version of the ¿h-product, which is a generalization of the classical direct product of graphs and, motivated by the ¿h-product, we also recover a generalization of the classical lexicographic product of graphs, namely the °h-product, that was introduced by Sabidussi in 1961. We provide two characterizations for the connectivity of G¿hG that generalize the existing one for the direct product. For G°hG, we provide exact formulas for the connectivity and the edge-connectivity, under the assumption that V (F) = V , for all F¿G. We also introduce some miscellaneous results about other invariants in terms of the factors of both, the ¿h-product and the °h-product. Some of them are easily obtained from the corresponding product of two graphs, but many others generalize the existing ones for the direct and the lexicographic product, respectively. We end up the paper by presenting some structural properties. An interesting result in this direction is a characterization for the existence of a nontrivial decomposition of a given graph G in terms of ¿h-product.
Thu, 21 Jan 2016 12:47:46 GMThttp://hdl.handle.net/2117/818042016-01-21T12:47:46ZLópez Masip, Susana ClaraMuntaner Batle, Francesc AntoniFigueroa-Centeno et al. [4] introduced the following product of digraphs let D be a digraph and let G be a family of digraphs such that V (F) = V for every F¿G. Consider any function h:E(D)¿G. Then the product D¿hG is the digraph with vertex set V(D)×V and ((a,x),(b,y))¿E(D¿hG) if and only if (a,b)¿E(D) and (x,y)¿E(h(a,b)). In this paper, we deal with the undirected version of the ¿h-product, which is a generalization of the classical direct product of graphs and, motivated by the ¿h-product, we also recover a generalization of the classical lexicographic product of graphs, namely the °h-product, that was introduced by Sabidussi in 1961. We provide two characterizations for the connectivity of G¿hG that generalize the existing one for the direct product. For G°hG, we provide exact formulas for the connectivity and the edge-connectivity, under the assumption that V (F) = V , for all F¿G. We also introduce some miscellaneous results about other invariants in terms of the factors of both, the ¿h-product and the °h-product. Some of them are easily obtained from the corresponding product of two graphs, but many others generalize the existing ones for the direct and the lexicographic product, respectively. We end up the paper by presenting some structural properties. An interesting result in this direction is a characterization for the existence of a nontrivial decomposition of a given graph G in terms of ¿h-product.A BRILS metaheuristic for non-smooth flow-shop problems with failure-risk costs
http://hdl.handle.net/2117/81738
A BRILS metaheuristic for non-smooth flow-shop problems with failure-risk costs
Ferrer Biosca, Alberto; Guimarans, Daniel; Ramalhino Lourenço, Helena; Juan Pérez, Ángel Alejandro
This paper analyzes a realistic variant of the Permutation Flow-Shop Problem (PFSP) by considering a non-smooth objective function that takes into account not only the traditional makespan cost but also failure-risk costs due to uninterrupted operation of machines. After completing a literature review on the issue, the paper formulates an original mathematical model to describe this new PFSP variant. Then, a Biased-Randomized Iterated Local Search (BRILS) algorithm is proposed as an efficient solving approach. An oriented (biased) random behavior is introduced in the well-known NEH heuristic to generate an initial solution. From this initial solution, the algorithm is able to generate a large number of alternative good solutions without requiring a complex setting of parameters. The relative simplicity of our approach is particularly useful in the presence of non-smooth objective functions, for which exact optimization methods may fail to reach their full potential. The gains of considering failure-risk costs during the exploration of the solution space are analyzed throughout a series of computational experiments. To promote reproducibility, these experiments are based on a set of traditional benchmark instances. Moreover, the performance of the proposed algorithm is compared against other state-of-the-art metaheuristic approaches, which have been conveniently adapted to consider failure-risk costs during the solving process. The proposed BRILS approach can be easily extended to other combinatorial optimization problems with similar non-smooth objective functions.
Wed, 20 Jan 2016 13:51:16 GMThttp://hdl.handle.net/2117/817382016-01-20T13:51:16ZFerrer Biosca, AlbertoGuimarans, DanielRamalhino Lourenço, HelenaJuan Pérez, Ángel AlejandroThis paper analyzes a realistic variant of the Permutation Flow-Shop Problem (PFSP) by considering a non-smooth objective function that takes into account not only the traditional makespan cost but also failure-risk costs due to uninterrupted operation of machines. After completing a literature review on the issue, the paper formulates an original mathematical model to describe this new PFSP variant. Then, a Biased-Randomized Iterated Local Search (BRILS) algorithm is proposed as an efficient solving approach. An oriented (biased) random behavior is introduced in the well-known NEH heuristic to generate an initial solution. From this initial solution, the algorithm is able to generate a large number of alternative good solutions without requiring a complex setting of parameters. The relative simplicity of our approach is particularly useful in the presence of non-smooth objective functions, for which exact optimization methods may fail to reach their full potential. The gains of considering failure-risk costs during the exploration of the solution space are analyzed throughout a series of computational experiments. To promote reproducibility, these experiments are based on a set of traditional benchmark instances. Moreover, the performance of the proposed algorithm is compared against other state-of-the-art metaheuristic approaches, which have been conveniently adapted to consider failure-risk costs during the solving process. The proposed BRILS approach can be easily extended to other combinatorial optimization problems with similar non-smooth objective functions.