This thesis consists of six papers. In Paper I, we give an algorithm for merging sorted lists of monomials and together with a projection technique, we obtain a new complexity bound for the Buchberger-Möller algorithm and the FGLM algorithm. In Paper II, we discuss four different constructions of vector space bases associated to vanishing ideals of points. We show how to compute normal forms with respect to these bases and give complexity bounds. As an application we drastically improve the computational algebra approach to the reverse engineering of gene regulatory networks. In Paper III, we introduce the concept of multiplication matrices for ideals of projective dimension zero. We discuss various applications and, in particular, we give a new algorithm to compute the variety of an ideal of projective dimension zero. In Paper IV, we consider a subset of projective space over a finite field and give a geometric description of the minimal degree of a non-vanishing form with respect to this subset. We also give bounds on the minimal degree in terms of the cardinality of the subset. In Paper V, we study an associative version of an algorithm constructed to compute the Hilbert series for graded Lie algebras. In the commutative case we use Gotzmann's persistence theorem to show that the algorithm terminates in finite time. In Paper VI, we connect the commutative version of the algorithm in Paper V with the Buchberger algorithm. / At the time of doctoral defence, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript

Evaluation codes (also called order domain codes) are traditionally introduced as generalized one point geometric Goppa codes. In the present dissertation we will give a new point of view on evaluation codes by introducing them instead as particular nice examples of affine variety codes. Our study includes a reformulation of the usual methods to estimate the minimum distances of evaluation codes into the setting of affine variety codes. Finally we describe the connection to the theory of one point geometric Goppa codes. / Códigos de avaliação (também chamados códigos de domínio de ordem) são tradicionalmente apresentados como códigos de Goppa de um ponto generalizados. Na presente dissertação, vamos estudar um novo ponto de vista sobre códigos de avaliação, introduzindo-os como bons exemplos particulares de códigos de variedades afins. Nosso estudo inclui uma reformulação dos métodos usuais para estimar as distâncias mínimas de códigos de avaliação no conjunto dos códigos de variedades afins. Finalmente descrevemos a conexão com a teoria dos códigos geométricos Goppa de um ponto. / Mestre em Matemática

In this paper, we consider affine varieties in vector space to analyze and understand the geometric behavior of sets solutions of systems of linear equations, solutions of linear ordinary differential equations of second order resulting from mathematical modeling of systems, etc. We observed characteristics of affine varieties in vector spaces as a subspaces vector transferred to any vector belonging to affine variety and do a comparison of geometric representations of the solution sets of problem situations, cited above, with such features. / Neste trabalho, consideramos variedades afins no espaÃo vetorial para analisar e compreender o comportamento geomÃtrico de conjuntos soluÃÃes de sistemas de equaÃÃes lineares, de soluÃÃes de equaÃÃes diferenciais ordinÃrias lineares de segunda ordem resultantes de modelagens matemÃticas de sistemas, etc. Verificamos caracterÃsticas das variedades afins em espaÃos vetoriais como um subespaÃo vetorial transladado de qualquer vetor pertencente à variedade afim e fazemos uma comparaÃÃo das representaÃÃes geomÃtricas dos conjuntos soluÃÃes das situaÃÃes-problema, citados acima, com tais caracterÃsticas.