Coherent Functors and Covariantly Finite Subcategories

Given a locally presentable additive category A, we study a class of covariantly finite subcategories which we call definable. A definable subcategory arises from a set of coherent functors F _i on A by taking all objects X in A such that F _i X=0 for all i. We give various characterizations of definable subcategories, demonstrating that all covariantly finite subcategories which arise in practice are of this form. This is based on a filtration of the category of all coherent functors on A.     

MAXIMUM TREES OF FINITE SEQUENCES

ＭＡＸＩＭＵＭＴＲＥＥＳＯＦＦＩＮＩＴＥＳＥＱＵＥＮＣＥＳ￥ＷＵＳＨＩＱＵＡＮＡｂｓｔｒａｃｔ：Ｌｅｔｎ，ｓ１，ｓ２，．．．，ｓｎｂｅｎｏｎ－ｎｅｇａｔｉｖｅｉｎｔｅｇｅｒｓａｎｄＭ（ｓ１，ｓ２，．．．，ｓｎ）＝｛（ａ１，ａ２，．．．，ａ．）｜ａｉｉ...     

Approximations and cotorsion pairs related to a tilting pair

The notion of a tilting pair Miyashita in 2001. It is a useful tool in cotorsion pairs related to a fixed tilting （covariantly） finite subcategory and a tilting pair were given in this paper. over artin algebras was introduced by the tilting theory. Approximations and pair were discussed. A eontravariantly eotorsion pair associated with a fixed     

伽罗瓦环上的一类No序列的构造

近年来,伽罗瓦环上的序列理论成为人们研究的热点问题.有限域上的No序列是一类伪随机序列,它在序列密码中占具十分重要的角色.本文利用伽罗瓦环上的置换,构造了伽罗瓦环Z_(p~e)上的一类新的No序列,并且研究了其线性复杂度.研究的结果表明此类No序列具有相当大的线性复杂度.     

Gröbner bases of characteristic ideals of LRS over UFD

LetR be a unique factorization domain (UFD). A method of Gröbner bases and localization in commutative algebra is applied to compute and analyze the characteristic ideals of semi-infinite linear recurring sequences (lrs), infinite linear recurring sequences (LRS), and finite lrs over UFD. The canonical form of a minimal Gröbner basis of the homogeneous characteristic ideal is described for a finite segment of an lrs, from which a precise relation between every step in the classical Berlekamp-Massey algorithm and every member of the Gröbner basis is derived.     

τ-Categories II: Nakayama Pairs and Rejective Subcategories

We study Nakayama pairs in τ-categories, which are pairs of objects connected by a certain diagram of Auslander–Reiten sequences. Using them, we naturally introduce orderlikeτ-categories. Then we study rejective subcategories of τ-categories. A typical example of orderlike τ-categories is given by the category of lattices over an order. In this case, its rejective subcategories correspond bijectively to its overrings. Presented by K. Roggenkamp Mathematics Subject Classifications (2000) Primary: 16G30; secondary: 16E65, 16G70, 18E05. Osamu Iyama: Current address: Department of Mathematics, University of Hyogo, Himeji 671-2201, Japan. e-mail: iyama@sci.u-hyogo.ac.jp     

Bent序列的相关值分布的研究

对已知的Bent序列集的构造方法作了研究,明确地给出了任一Bent序列集相关值的分配情况.同时,利用有限域上一类新的Bent函数,构造出了一类新的Bent序列集,给出了这类Bent序列的线性复杂度.     

Finite-automaton transformations of strictly almost-periodic sequences

Different versions of the notion of almost-periodicity are natural generalizations of the notion of periodicity. The notion of strict almost-periodicity appeared in symbolic dynamics, but later proved to be fruitful in mathematical logic and the theory of algorithms as well. In the paper, a class of essentially almost-periodic sequences (i.e., strictly almost-periodic sequences with an arbitrary prefix added at the beginning) is considered. It is proved that the property of essential almost-periodicity is preserved under finite-automaton transformations, as well as under the action of finite transducers. The class of essentially almost-periodic sequences is contained in the class of almost-periodic sequences. It is proved that this inclusion is strict.     

关于遗传代数上的例外序列自同态代数的Hochschild上同调与同调

令$A$是代数闭域$k$上的一个有限维结合代数, $\mod A$是有限维左$A$-模范畴,$X_1,X_2,\ldots,X_n$是$\mod A$中的完全例外序列,再令$E$是$X_1,X_2,\ldots,X_n$的自同态代数,我们在本文内,研究了$E$的总体维数,计算了$E$的Hochschild上同调群和同调群.     

Tilting subcategories in extriangulated categories

Extriangulated category was introduced by H.Nakaoka and Y.Palu to give a unification of properties in exact categories anjd triangulated categories.A notion of tilting(resp.,cotilting)subcategories in an extriangulated category is defined in this paper.We give a Bazzoni characterization of tilting(resp.,cotilting)subcategories and obtain an Auslander-Reiten correspondence between tilting(resp.,cotilting)subcategories and coresolving covariantly(resp.,resolving contravariantly)finite subcatgories which are closed under direct summands and satisfy some cogenerating(resp.,generating)conditions.Applications of the results are given:we show that tilting(resp.,cotilting)subcategories defined here unify many previous works about tilting modules(subcategories)in module categories of Artin algebras and in abelian categories admitting a cotorsion triples;we also show that the results work for the triangulated categories with a proper class of triangles introduced by A.Beligiannis.     

带非线性边界条件的反应扩散方程的数值方法

１引言近年来关于非线性抛物型方程数值解法的研究取得了许多好的结果,其中以Ｃ．Ｖ．Ｐａｏ为主的研究者们利用上、下解方法对带线性边界条件的半线性抛物型方程的有限差分系统进行了广泛的研究,提出了一系列有效的迭代算法（见［１］、［２］、［３］、［４］）．但对带非线性边界条件的半线性抛物型方程初边值问题,作者至今尚未见到有研究者将上、下解方法用在相应的差分系统上,求得数值解．其主要原因是由于边界上函数的非线性,解在边界网格点上的值未知且无法用内部网格点上的值直接表示,相应的差分系统表示形式受到影响,边界网…     

Normal sequences over finite abelian groups

In this note, we obtain the structure of short normal sequences over a finite abelian p-group or a finite abelian group of rank two, thus answering positively a conjecture of Gao and Zhuang for various groups. The results obtained here improve all known results on this conjecture.     

Solving Thue equations without the full unit group

The main problem when solving a Thue equation is the computation of the unit group of a certain number field. In this paper we show that the knowledge of a subgroup of finite index is actually sufficient. Two examples linked with the primitive divisor problem for Lucas and Lehmer sequences are given.

     

Periodicity and Correlation Properties of d-FCSR Sequences

A d-feedback-with-carry shift register (d-FCSR) is a finite state machine, similar to a linear feedback shift register (LFSR), in which a small amount of memory and a delay (by d-clock cycles) is used in the feedback algorithm (see Goresky and Klapper [4,5]). The output sequences of these simple devices may be described using arithmetic in a ramified extension field of the rational numbers. In this paper we show how many of these sequences may also be described using simple integer arithmetic, and consequently how to find such sequences with large periods. We also analyze the arithmetic cross-correlation between pairs of these sequences and show that it often vanishes identically.     

A Note on Sequences with the Shift and Add Property

A sequence of elements from a finite field satisfies the shift and add property if the componentwise sum of any two shifts of the sequence is either a shift of the sequence or the all zero sequence. A sequence whose elements lie in an arbitrary group satisfies the shift and multiply property if the componentwise product of any two shifts of the sequence is either a shift of the sequence or the all identity sequence. The paper classifies sequences which have the shift and add property or the shift and multiply property.     

A case study in meta-automation: automatic generation of congruence automata for combinatorial sequences

In this paper, which may be considered a sequel to a recent article by Eric Rowland and Reem Yassawi, we present yet another approach for the automatic generation of automata (and an extension that we call congruence linear schemes) for the fast (log-time) determination of congruence properties, modulo small (and not so small!) prime powers, for a wide class of combinatorial sequences. Even more interesting than the new results that could be obtained is the illustrated methodology, that of designing ‘meta-algorithms’ that enable the computer to develop algorithms, that it (or another computer) can then proceed to use to actually prove (potentially!) infinitely many new results. This paper is accompanied by a Maple package, AutoSquared, and numerous sample input and output files, that readers can use as templates for generating their own, thereby proving many new ‘theorems’ about congruence properties of many famous (and, of course, obscure) combinatorial sequences.     

$T_{2}(T)$的几乎可裂序列及几乎$\mathcal {D}$-可裂序列

The AR-quiver and derived equivalence are two important subjects in the representation theory of finite dimensional algebras, and for them there are two important research tools-AR-sequences and D-split sequences. So in order to study the representations of triangular matrix algebra T2 (T ) = T0TT where T is a finite dimensional algebra over a field, it is important to determine its AR-sequences and D-split sequences. The aim of this paper is to construct the right(left) almost split morphisms, irreducible morphisms, almost split sequences and D-split sequences of T2 (T) through the corresponding morphisms and sequences of T. Some interesting results are obtained.     

Right n-angulated categories arising from covariantly finite subcategories

We define right n-angulated categories, which are analogous to right triangulated categories. Let 𝒞 be an additive category and 𝒳 a covariantly finite subcategory of 𝒞. We show that under certain conditions, the quotient 𝒞∕[𝒳] is a right n-angulated category. This has immediate applications to n-angulated quotient categories.     

A primal-dual algorithm for the fermat-weber problem involving mixed gauges

We give a new algorithm for solving the Fermat-Weber location problem involving mixed gauges. This algorithm, which is derived from the partial inverse method developed by J.E. Spingarn, simultaneously generates two sequences globally converging to a primal and a dual solution respectively. In addition, the updating formulae are very simple; a stopping rule can be defined though the method is not dual feasible and the entire set of optimal locations can be obtained from the dual solution by making use of optimality conditions. When polyhedral gauges are used, we show that the algorithm terminates in a finite number of steps, provided that the set of optimal locations has nonepty interior and a counterexample to finite termination is given in a case where this property is violated. Finally, numerical results are reported and we discuss possible extensions of these results.     

Linearity of stability conditions

Abstract

For modules over an artin algebra, a linear stability condition is given by a “central charge” and a nonlinear stability condition is given by the wall-crossing sequence of a “green path.” Finite Harder-Narasimhan stratifications of the module category, maximal forward hom-orthogonal sequences and maximal green sequences, defined using Fomin-Zelevinsky quiver mutation are shown to be equivalent to finite nonlinear stability conditions when the algebra is hereditary. This is the first of a series of three papers whose purpose is to determine all maximal green sequences of maximal length for quivers of affine type A and determine which are linear.