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David Llena

Publications and source records attributed to David Llena.

4 recordsLinked to original sources
arXiv2021

Factorization in monoids by stratification of atoms and the Elliott Problem

In an additive factorial monoid each element can be represented as a linear combination of irreducible elements (atoms) with uniquely determined coefficients running over all natural numbers. In this paper we develop for a wide class of non-factorial monoids a concept of stratification for atoms which allows to represent each element as a linear combination of atoms where the coefficients are uniquely determined when restricted in a particular way. This wide class includes inside factorial monoids and in particular simplicial affine semigroups. In the latter case the question of uniqueness is related to a problem studied by E. B. Elliott in a paper from 1903. For the monoid of all nonnegative solutions of a certain linear Diophantine equation in three variables, Elliott considers "simple sets of solutions" (atoms of the monoid) and looks for a method that gives "every set once only". We show that for simplicial affine semigroups in two dimensions a stratification is always possible, which answers to Elliott's problem also for the cases he left open. The results in this paper on the stratification of atoms for monoids in general may be seen also as an answer to a "generalized Elliott problem".

math.NT↗
arXiv2018

Inside factorial monoids and the cale monoid of a single Diophantine equation

We give a structure theorem for inside factorial domains. As an example we study the monoid of nonnegative integer solutions of equations of the form $a_1x_1+\cdots +a_{r-1}x_{r-1}=a_rx_r$, with $a_1,\ldots,a_r$ positive integers. This set is isomorphic to a simplicial full affine semigroup, and thus it can be described in terms of its extremal rays and the Apéry sets with respect to the extremal rays.

math.AC↗
arXiv2003

Lie bracket of vector fields in noncommutative geometry

The aim of this paper is to avoid some difficulties, related with the Lie bracket, in the definition of vector fields in a non commutative setting, as they were defined by Woronowicz, Schmudgen--Schuler and Aschieri--Schupp. We extend the definition of vector fields to consider them as derivations of the algebra, through Cartan pairs introduced by Borowiec. Then, using translations, we introduce the invariant vector fields. Finally, the definition of Lie bracket realized by Dubois--Violette, considering elements in the center of the algebra, is also extended to these invariant vector fields.

math.RA↗