On the number of terms in the middle of almost split sequences over cycle-finite artin algebras
We prove that the number of terms in the middle of an almost split sequence in the module category of a cycle-finite artin algebra is bounded by 5.
Minimal decision rules based on the apriori algorithm
Based on rough set theory many algorithms for rules extraction from data have been proposed. Decision rules can be obtained directly from a database. Some condition values may be unnecessary in a decision rule produced directly from the database. Such values can then be eliminated to create a more comprehensible (minimal) rule. Most of the algorithms that have been proposed to calculate minimal rules are based on rough set theory or machine learning. In our approach, in a post-processing stage,...
Cuadrados mágicos de primos.
On the tameness of trivial extension algebras
For a finite dimensional algebra A over an algebraically closed field, let T(A) denote the trivial extension of A by its minimal injective cogenerator bimodule. We prove that, if is a tilting module and , then T(A) is tame if and only if T(B) is tame.
Commutativity and non-commutativity of topological sequence entropy
In this paper we study the commutativity property for topological sequence entropy. We prove that if is a compact metric space and are continuous maps then for every increasing sequence if , and construct a counterexample for the general case. In the interim, we also show that the equality is true if but does not necessarily hold if is an arbitrary compact metric space.
Computing explicitly topological sequence entropy: the unimodal case
Let denote the family of continuous maps from an interval into itself such that (1) ; (2) they consist of two monotone pieces; and (3) they have periodic points of periods exactly all powers of . The main aim of this paper is to compute explicitly the topological sequence entropy of any map respect to the sequence .
On the deformation theory of finite dimensional algebras.
On minimal non-tilted algebras
A minimal non-tilted triangular algebra such that any proper semiconvex subcategory is tilted is called a tilt-semicritical algebra. We study the tilt-semicritical algebras which are quasitilted or one-point extensions of tilted algebras of tame hereditary type. We establish inductive procedures to decide whether or not a given strongly simply connected algebra is tilted.
Relative Auslander-Reiten sequences for quasi-hereditary algebras
Let A be a finite-dimensional algebra which is quasi-hereditary with respect to the poset (Λ, ≤), with standard modules Δ(λ) for λ ∈ Λ. Let ℱ(Δ) be the category of A-modules which have filtrations where the quotients are standard modules. We determine some inductive results on the relative Auslander-Reiten quiver of ℱ(Δ).
Trisections of module categories
Let A be a finite-dimensional algebra over a field k. We discuss the existence of trisections (mod₊ A,mod₀ A,mod₋ A) of the category of finitely generated modules mod A satisfying exactness, standardness, separation and adjustment conditions. Many important classes of algebras admit trisections. We describe a construction of algebras admitting a trisection of their module categories and, in special cases, we describe the structure of the components of the Auslander-Reiten quiver lying in mod₀ A.
Galois coverings and the problem of axiomatization of the representation type of algebras.
Substructures of algebras with weakly non-negative Tits form.
Let A = kQ/I be a finite dimensional basic algebra over an algebraically closed field k presented by its quiver Q with relations I. A fundamental problem in the representation theory of algebras is to decide whether or not A is of tame or wild type. In this paper we consider triangular algebras A whose quiver Q has no oriented paths. We say that A is essentially sincere if there is an indecomposable (finite dimensional) A-module whose support contains all extreme vertices of Q. We prove that if...
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