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Displaying 61 – 80 of 555

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Betti numbers of some circulant graphs

Mohsen Abdi Makvand, Amir Mousivand (2019)

Czechoslovak Mathematical Journal

Let o ( n ) be the greatest odd integer less than or equal to n . In this paper we provide explicit formulae to compute -graded Betti numbers of the circulant graphs C 2 n ( 1 , 2 , 3 , 5 , ... , o ( n ) ) . We do this by showing that this graph is the product (or join) of the cycle C n by itself, and computing Betti numbers of C n * C n . We also discuss whether such a graph (more generally, G * H ) is well-covered, Cohen-Macaulay, sequentially Cohen-Macaulay, Buchsbaum, or S 2 .

Bornes pour la régularité de Castelnuovo-Mumford des schémas non lisses

Amadou Lamine Fall (2009)

Annales de l’institut Fourier

Nous montrons dans cet article des bornes pour la régularité de Castelnuovo-Mumford d’un schéma admettant des singularités, en fonction des degrés des équations définissant le schéma, de sa dimension et de la dimension de son lieu singulier. Dans le cas où les singularités sont isolées, nous améliorons la borne fournie par Chardin et Ulrich et dans le cas général, nous établissons une borne doublement exponentielle en la dimension du lieu singulier.

Bounds on Castelnuovo-Mumford regularity for divisors on rational normal scrolls.

Chikashi Miyazaki (2005)

Collectanea Mathematica

The Castelnuovo-Mumford regularity is one of the most important invariants in studying the minimal free resolution of the defining ideals of the projective varieties. There are some bounds on the Castelnuovo-Mumford regularity of the projective variety in terms of the other basic invariants such as dimension, codimension and degree. This paper studies a bound on the regularity conjectured by Hoa, and shows this bound and extremal examples in the case of divisors on rational normal scrolls.

Bounds on multisecant lines.

Scott Nollet (1998)

Collectanea Mathematica

The purpose of this paper is twofold. First, we give an upper bound on the order of a multisecant line to an integral arithmetically Cohen-Macaulay subscheme in Pn of codimension two in terms of the Hilbert function. Secondly, we give an explicit description of the singular locus of the blow up of an arbitrary local ring at a complete intersection ideal. This description is used to refine a standard linking theorem. These results are tied together by the construction of sharp examples for the bound,...

C -Gorenstein projective, injective and flat modules

Xiao Yan Yang, Zhong Kui Liu (2010)

Czechoslovak Mathematical Journal

By analogy with the projective, injective and flat modules, in this paper we study some properties of C -Gorenstein projective, injective and flat modules and discuss some connections between C -Gorenstein injective and C -Gorenstein flat modules. We also investigate some connections between C -Gorenstein projective, injective and flat modules of change of rings.

Caractères numériques et fonctions de Macaulay.

Mireille Martin-Deschamps (2004)

Collectanea Mathematica

The postulation of Aritméticamente Cohen-Macaulay (ACM) subschemes of the projective space PkN is well known in the case of codimension 2. There are many different ways of recording this numerical information: numerical character of Gruson/Peskine, h-vector, postulation character of Martin-Deschamps/Perrin... The first aim of this paper is to show the equivalence of these notions. The second and most important aim, is to study the postulation of codimension 3 ACM subschemes of PN. We use a result...

Currently displaying 61 – 80 of 555