Eduardo Saenz de Cabezon

arXiv2006

Computing Koszul Homology for Monomial Ideals

The Koszul homology of modules of the polynomial ring $R$ is a central object in commutative algebra.It is strongly related with the minimal free resolution of these modules, and thus with regularity, Hilbert functions, etc. Here we consider the case of modules of the form $R/I$ where $I$ is a monomial ideal. So far, some good algorithms have been given in the literature and implemented in different Computer Algebra Systems (e.g. CoCoa, Singular, Macaulay), which compute minimal free resolutions of modules of the form $R/I$ with $I$ an ideal in $R$, which include the case of $I$ being a monomial ideal as a particular one (a good review is given in \cite {Sie}). Our goal is to build algorithms especially teargeted to monomial ideals, taking into account the special combinatorial and structural properties of these ideals. This being a first goal, it is also a first step of an alternative approach to the computation of the Koszul homology and minimal free resolutions of polynomial ideals.

math.AC↗

arXiv2003

Bordered magic squares: elements for a comprehensive approach

General methods for the construction of magic squares of any order have been searched for centuries. There have been several standard strategies for this purpose, such as the knight movement, or the construction of bordered magic squares, which played an important role in the development of general methods. What we try to do here is to give a general and comprehensive approach to the construction of magic borders, capable of assuming methods produced in the past like particular cases. This general approach consists of a transformation of the problem of constructing magic borders to a simpler - almost trivial - form. In the first section, we give some definitions and notation. The second section consists of the exposition and proof of our method for the diferent cases that appear (theorems 1 and 2). Although methods for the construction of bordered magic squares have always been presented as individual succesful attempts to solve the problem, we will see that a common pattern underlies the fundamental mechanisms that lead to the construction of such squares. This approach provides techniques for constructing many magic bordered squares of any order, which is a first step to construct all of them, and finally know how many bordered squares are for any order. These may be the first elements of a general theory on bordered magic squares.

math.CO↗