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We tackle the obtaining of canonical forms for classifying linear control systems with regard to changes in the state variables. Although it was solved in the 1980s for controllable systems, it is still an open problem for the general case of multiparametric non-necessarily controllable systems. Here we obtain a general reduced form which is canonical for a class of systems which includes the cases already known (uniparametric systems, controllable systems), Peer Reviewed, Postprint (published version)

The classification of invariant subspaces is an open problem related to other important ones like the Carlson problem. Here we obtain a reduced form of these invariant subspaces as a new tool to tackle these problems. In particular, it allows us to prove quite easily partial results already known. The key point is assigning to each invariant subspace a marked one (its marked type) in order to partition the set of invariant subspaces in a finite number of subsets (the marked classes), each one containing only one marked subspace. Next, we parametrize (minimally) each marked class by means of the so-called PM reduced families, so that representatives of an invariant subspace (its PM reduced forms) appear in just one of these families., Peer Reviewed, Postprint (author's final draft)

We continue the study of the structural stability and the bifurcations of planar continuous bimodal linear dynamical systems (that is, systems consisting of two linear dynamics acting on each side of a straight line, assuming continuity along the separating line). Here, we complete the study when one of the subsystems is a saddle, leading to a 3D bifurcation diagram where a large catalogue of bifurcations appears: four surfaces of codimension-1 bifurcations; two sequences of surfaces of additional codimension-1 bifurcations; two lines of codimension-2 bifurcations; and one codimension-3 bifurcation., Peer Reviewed, Postprint (author's final draft)

Fluxos en xarxes, a càrrec de Josep Ferrer Llop (Dept. Matemàtiques UPC) Dimecres 25/04/2018 Aula 004 FME 12-13h30

We complete the study of the bifurcations of saddle/spiral bimodal linear systems, depending on the respective traces T and t: one 2-codimensional bifurcation; four kinds of 1-codimensional bifurcations. We stratify the bifurcation set in the (T,t)-plane and we describe the qualitative changes of the dynamical behavior at each bifurcation point., Peer Reviewed, Postprint (author's final draft)

El projecte es basa en el conjunt de publicacions del Departament de Matemàtica Aplicada I de la UPC sobre els subespais invariants. Els estudis del departament són entorn les deformacions que experimenten els objectes dels sistemes de control lineal, analitzant com varien les propietats i com resulta el sistema quan aquest és sotmès a petites pertorbacions. En particular, es treballarà amb els subespais invariants i, més específicament, els subespais marcats. Actualment s’està estudiant la classificació d’aquests subespais invariants, en la qual contribuirem amb els resultats que s’obtinguin d’aquest projecte. Treballarem amb les representacions dels subespais invariant mitjançant matrius BLD (Block Lower Diagonal), de les quals obtindrem la màxima simplificació. El projecte consisteix doncs, en l’obtenció d’un programa que permeti arribar de manera fàcil, ràpida i segura a la matriu BLD en la seva forma reduïda. Així, en la primera fase del projecte es realitza un estudi de la teoria per obtenir la forma marcada maximal reduïda d’una matriu BLD i les possibles opcions que hi poden haver a l’hora de programar l’algoritme. Posteriorment es mostra com s’utilitza el programa, dissenyat amb Office Excel, d’una manera senzilla, amb una interfície dissenyada per ser fàcil d’entendre i manipular. A continuació es detalla el funcionament de l’algorisme programat per a l’obtenció de les formes reduïdes, especificant l’estructura interna d’aquest per tal d’entendre el codi si es desitja modificar-lo. Finalment s’analitzen els resultats que s’obtenen en aplicar l’algoritme per diferents formes de la matriu BLD, obtenint la deformació miniversal correcte i les formes reduïdes maximal marcades. S’observa com, per matrius BLD de mateixes dimensions però amb valors diferents, s’obté una mateixa forma reduïda maximal marcada.

We continue the study of the structural stability and the bifurcations of planar bimodal linear dynamical systems (BLDS) (that is, systems consisting of two linear dynamics acting on each side of a straight line, assuming continuity along the separating line). Here, we enlarge the study of the bifurcation diagram of saddle/spiral BLDS to saddle/source BLDS and in particular we study the position of the homoclinic bifurcation with regard to the new improper node bifurcation, Postprint (published version)

The aim of this thesis is to study the hyperinvariant and characteristic subspaces of a matrix, or equivalently, of an endomorphism of a finite dimensional vector space. We restrict ourselves to the case of matrices A with an splitting characteristic polynomial, leaving for future work the generalization for any characteristic polynomial. The subspaces A-hyperinvariant and A-characteristic are subclasses of A-invariant subspaces (those containing its image for A), a key concept in the theory of matrices. Specifically, the subspaces A-hiperinvariant are those that are also invariant for all matrices that commute with A, while the A characteristic are required that are only invariant for invertible matrices that commute with A. Both concepts first appeared in the mid-30s within the context of group theory. But it was not until the 70s that appears a characterization of the A-hiperinvariant subspaces and their lattice was described in the context of matrix theory. In 2009 appears an article of Astuti and Wimmer which shows that A-hyperinvariant and A-caracteristic subspaces are the same except in the field GF(2) . In this case, Shoda theorem gives necessary and sufficient conditions for the existence of characteristic non-hiperinvariant subspaces. But the description of these subspaces was an open problem which is solved in this thesis. Our first objective, therefore, is to analyze the behavior of the centralizer of a matrix (i.e., the set of matrices commuting with it), we will assume canonical form ( Jordan or Weyr). Specifically, we calculate the determinant of the matrices in the centralizer, which in particular allows to characterize the nonsingular. Furthermore, we determined the images of a given subspace respect to the set of all matrices of these centralizers, a result that will be key for further study of hiperinvariant subspaces. We begin this study, giving conditions for the existence of one-dimensional hiperinvariant subspaces. More generally, using the re, El objetivo principal de esta tesis es estudiar en profundidad los subespacios hiperinvariantes y característicos de una matriz, o equivalentemente, de un endomorfismo de un espacio vectorial de dimensión finita. Nos restringimos al caso de matrices A con polinomio característico totalmente descomponible, dejando para futuros trabajos la generalización para cualquier polinomio característico. Los subespacios A-hiperinvariantes y A-característicos son subclases de los subespacios A-invariantes (aquellos que contienen su imágen por A), concepto clave en la teoría de matrices. Concretamente, los subespacios A-hiperinvariantes son aquellos que también son invariantes para toda matriz que conmuta con A, mientras que a los A-característicos se les exige sólo que lo sean para las matrices inversibles que conmutan con A. Ambos conceptos aparecen por primera vez a mediados de los años 30 dentro del contexto de la teoría de grupos. Pero no es hasta los años 70 en que se da una caracterización de los subespacios A-hiperinvariantes y se describe su retículo dentro de la teoría de matrices. En el año 2009 aparece un artículo de Astuti y Wimmer donde se demuestra que en el caso de matrices A con polinomio característico totalmente descomponible, los subespacios característicos coinciden con los hiperinvariantes excepto si los coeficientes de A pertenecen a GF(2). En este casos, el Teorema de Shoda da condiciones necesarias y suficientes para la existencia de subespacios característicos no hiperinvariantes. Pero la descripción de este tipo de subespacios era un problema abierto que resolvemos en esta tesis. Nuestro primer objetivo, por tanto, será analizar el comportamiento del centralizador de una matriz, (esto es, el conjunto de matrices que conmutan con ella), que supondremos en forma canónica (de Jordan o de Weyr). Concretamente, calculamos el determinante de las matrices de dichos centralizadores, lo que en particular, permite caracterizar las no singulares. Por otra parte, d, Postprint (published version)

We present a geometric approach to the classification of monogenic invariant subspaces, alternative to the classical algebraic one, which allows us to obtain several matricial canonical forms for each class. Some applications are derived: canonical coordinates of a vector with regard to an endomorphism, and a canonical form for uniparametric linear control systems, not necessarily controllable, with regard to linear changes of state variables. Moreover, the pointwise construction can be extended to differentiable families of changes of basis when differentiable families of equivalent monogenic subspaces are considered., Peer Reviewed, Postprint (author’s final draft)

We consider bimodal linear control systems consisting of two subsystems acting on each side of a given hyperplane, assuming continuity along it. For a differentiable family of planar bimodal linear control systems, we obtain its stratification diagram and, if controllability holds for each value of the parameters, we construct a differentiable family of feedbacks which stabilizes both subsystems for each value of the parameters., Postprint (published version)

Structural stability ensures that the qualitative behavior of a system is preserved under small perturbations. We study it for planar bimodal linear dynamical systems, that is, systems consisting of two linear dynamics acting on each side of a given hyperplane and assuming continuity along the separating hyperplane. We describe which one of these systems is structurally stable when (real) spiral does not appear and when it does we give necessary and sufficient conditions concerning finite periodic orbits and saddle connections. In particular, we study the finite periodic orbits and the homoclinic orbits in the saddle/spiral case., Postprint (published version)

Given the set of vertical pairs of matrices ${\cal M}\subset M_{m,n}(\mathbb C)\times M_n(\mathbb C)$ keeping the subspace $\mathbb C^d\times\{0\}\subset\mathbb C^n$ invariant,we compute miniversal deformations of a given pair when it is observable, and the subspace $\mathbb C^d\times\{0\}$ is marked. Moreover, we obtain the dimension of the orbit, characterize the structurally stable vertical pairs, and study the effect of each deformation parameter. Copyright © 2013 JohnWiley & Sons, Ltd., Postprint (published version)

We consider bimodal linear dynamical systems consisting of two linear dynamics acting on each side of a given hyperplane, assuming continuity along the separating hyperplane. Focusing in the planar case, we describe which of these systems are structurally stable., Postprint (published version)

Let F be an arbitrary field, Mn(F) the set of all matrices n×n over F and J∈Mn(F) a Jordan matrix. In this paper, we obtain an explicit formula for the determinant of any matrix that commutes with J, i.e., the determinant of any element T∈Z(J), the centralizer of J. Our result can also be extended to any T′∈Z(A), where A∈Mn(F), can be reduced to J=S−1AS. This is because T=S−1T′S∈Z(J), and clearly View the MathML source. If F is algebraically closed, any matrix A can be reduced in this way to a suitable J. In order to achieve our main result, we use an alternative canonical form W∈Mn(F) called the Weyr canonical form. This canonical form has the advantage that all matrices K∈Z(W) are upper block triangular. The permutation similarity of T∈Z(J) and K∈Z(W) is exploited to obtain a formula for the determinant of T. The paper is organized as follows: Section 2 contains some definitions and notations that will be used through all the paper. In Section 3, matrices T∈Z(J) are described and the determinant of T is computed in a particular case. In Section 4, we recall the Weyr canonical form W of a matrix and the corresponding centralizer Z(W). A formula to compute the determinant of any K∈Z(W) is rewritten. Finally, in Section 5 an explicit formula for the determinant of any T∈Z(J) is obtained., Peer Reviewed, Postprint (published version)

We consider bimodal linear control systems consisting of two subsystems acting on each side of a given hyperplane, assuming continuity along the separating hyperplane. For a differentiable family of controllable planar ones, we construct a differentiable family of feedbacks which pointwise stabilizes both subsystems., Postprint (published version)

We consider bimodal linear systems consisting of two linear dynamics acting on each side of a given hyperplane, assuming continuity along the separating hyperplane. We prove that the study of controllability can be reduced to the unobservable case, and for these ones we obtain a simple explicit characterization of controllability for dimensions 2 and 3, as well as some partial criteria for higher dimensions., Postprint (published version)

Postprint (published version)

Given the set of vertical pairs of matrices M¿ Mm,n(C)×Mn(C) keeping the subspace Cd×{0} ¿ Cn invariant, we compute miniversal deformations of a given pair when it is observable and the subspace Cd × {0} is marked. Moreover, we obtain the dimension of the orbit, characterize the structurally stable vertical pairs and study the effect of each deformation parameter., Preprint

The classification of the invariant subspaces of an endomorphism has been an open problem for a long time, and it is a ”wild” problem in the general case. Here we obtain a full classification for the monogenic ones. Some applications are derived: in particular, canonical forms for uniparametric linear control systems, non necessarily controllable, with regard to linear changes of state variables, Preprint

Given the set of matrix pairsM Mm,n.C/ Mn.C/ keeping a subspace S Cn invariant, we obtain a miniversal deformation of a pair belonging to an open dense subset ofM. It generalizes the known results when S is a supplementary subspace of the unobservable one., Postprint (published version)

Given S an (A,B)-invariant subspace, we prove that the set of friend feedbacks is a linear variety, which can be considered as the direct sum of the feedbacks of the restriction to S and the co-restriction to S ⊥. In particular, when the natural controllability hypothesis hold, both pole assignments are simultaneously possible bymeans of a convenient friend feedback. Copyright, Peer Reviewed, Postprint (published version)

Given a pair of matrices representing a controllable linear system, its equivalence classes by the single or combined action of feedbacks, change of state and input variables, as well as their intersection are studied. In particular, it is proved that they are differentiable manifolds and their dimensions are computed. Some remarks concerning the effect of different kinds of feedbacks are derived., Postprint (published version)

Postprint (published version)

The set of controllable switched linear systems is an open set in the space of all switched linear systems. Then it makes sense to compute the distance from a controllable switched linear system to the set of uncontrollable systems. In this work we obtain an upper bound for such distance., Postprint (published version)

The Bologna process is a good opportunity to bring together first-year mathematics courses of engineering degrees and technology courses offered in subsequent years. In fact, the Faculty Council has decided that 20% of the credits from basic courses must be related to technological applications. To this end, during the past academic year a mathematical engineering seminar was held with each session dealing with one technological discipline. The main goal of the seminar, which relied on the presence of speakers from both mathematics and engineering departments, was to identify the most commonly used mathematical tools. Furthermore, a set of exercises and some guidelines addressed to faculty lacking an engineering background were created. Here, we present some of this material: first, a summary of the collection of exercises illustrating the use of Linear Algebra in different engineering areas such as Mechanical Engineering, Control and Automation, and second, some exercises, Postprint (published version)

Given a family of linear systems depending on a parameter varying in a differentiable manifold, we obtain sufficient conditions for the existence of a (global or local) differentiable family of controllers solving the output regulation problem for the given family. Moreover, we construct it when these conditions hold., Peer Reviewed, Postprint (published version)

Given a pair of matrices representing a controllable linear system, we study its equivalence classes by the single or combined action of feedbacks and change of state and input variables, as well as their intersections. In particular, we prove that they are differentiable manifolds and we compute their dimensions. Some remarks concerning the effect of different kinds of feedbacks are derived., Postprint (published version)

Given the set of matrix pairs M ⊂ Mm,n(C) × Mn(C) keeping a subspace S ⊂ Cn invariant, we obtain a miniversal deformation of a pair belonging to an open dense subset of M. It generalizes the known results when S is a supplementary subspace of the unobservable one., Postprint (published version)

Given a general local differentiable family of pairs of matrices, we obtain a local differentiable family of feedbacks solving the pole assignment problem, that is to say, shifting the spectrum into a prefixed one. We point out that no additional hypothesis is needed. In fact, simple approaches work in particular cases (controllable pairs, constancy of the dimension of the controllable subspace, and so on). Here the general case is proved by means of Arnold’s techniques: the key point is to reduce the construction to a versal deformation of the central pair; in fact to a quite singular miniversal one for which the family of feedbacks can be explicitly constructed. As a direct application, a differentiable family of stabilizing feedbacks is obtained, provided that the central pair is stabilizable., Postprint (published version)

Keywords: Bimodal piecewise linear system, miniversal deformations, reduced forms., Bimodal linear systems are those consisting of two linear systems on each side of a given hyperplane, having continuous dynamics along that hyperplane. In this work, we focus on the derivation of (orthogonal) miniversal deformations, by using reduced forms., Postprint (published version)

Se denuncian intentos de “privatización encubierta” de la universidad, esto es, de sometimiento de su docencia e investigación a los requerimientos de los demandantes privados, concretado por ejemplo en la planificación docente, las tasas académicas y los sistemas de gobierno. Tal mercantilización responde a una consideración, más o menos explícita, de la educación superior como una mercancía frente a la concepción de servicio público, al alcance de toda la sociedad. Se argumentan los principios básicos de este modelo social (autonomía universitaria, compromiso social, rendición de cuentas, financiación pública, gobierno participativo y democrático,…), y se alerta sobre diversas vías de penetración del modelo neoliberal (competitividad, jerarquización, gerencialización,…) y en particular sobre las campañas de desprestigio contra la universidad pública., The paper denounces the covert privatisation of university; in other words, the submission of its teaching and research to private interests. For example, concerning the teaching plan, the academic fees and the governance system. This commercialisation stems from considering higher education, more or less explicitly, as merchandise instead of as a public service made available to all levels of society. The basic principles of this social model (university autonomy, social commitment, accountability, public funding, participative and democratic governance…) are discussed in the paper. It also warns about the penetration of the neoliberal governance model (competitivity, hierarchisation, management…) and the systematic campaigns aimed at discrediting public university.