Let K be a field and let A = K[X1,...,Xn] be the polynomial ring in X1, ..., Xn with coefficients in K. In this paper we study the universal squarefree lexsegment ideals, and put our attention on their combinatorics c...Let K be a field and let A = K[X1,...,Xn] be the polynomial ring in X1, ..., Xn with coefficients in K. In this paper we study the universal squarefree lexsegment ideals, and put our attention on their combinatorics computing some invariants. Moreover, we study the link between such a special class of squarefree lexsegment ideals and the so-called s-sequences.展开更多
Let K be a field and let S = K[x1,...,xn] be a polynomial ring over K. Let F = ir=1 Sei be a finitely generated graded free S-module with basis {e1,..., er} in degrees f1,..., fr such that f1≤ f2 ~≤……≤ fr. We exa...Let K be a field and let S = K[x1,...,xn] be a polynomial ring over K. Let F = ir=1 Sei be a finitely generated graded free S-module with basis {e1,..., er} in degrees f1,..., fr such that f1≤ f2 ~≤……≤ fr. We examine some classes of squarefree monomial submodules of F. Hence, we focalize our attention on the Betti table of such classes in order to analyze the behavior of their extremal Betti numbers.展开更多
We compute the minimal primary decomposition for completely squarefree lexsegment ideals. We show that critical squarefree monomial ideals are sequentially Cohen- Macaulay. As an application, we give a complete charac...We compute the minimal primary decomposition for completely squarefree lexsegment ideals. We show that critical squarefree monomial ideals are sequentially Cohen- Macaulay. As an application, we give a complete characterization of the completely square- free lexsegment ideals which are sequentially Cohen-Macaulay and we also derive formulas for some homological invariants of this class of ideals.展开更多
Let S = K[x1, x2,..., xn] be the polynomial ring in n variables over a field K, and let I be a squarefree monomial ideal minimally generated by the monomials ul,u2,...,Um. Let w be the smallest number t with the prope...Let S = K[x1, x2,..., xn] be the polynomial ring in n variables over a field K, and let I be a squarefree monomial ideal minimally generated by the monomials ul,u2,...,Um. Let w be the smallest number t with the property that for all integers 1 ≤ i1 〈 i2 〈 … 〈 it ≤ m such that lcm（uil, ui2,..., uii） = lcm（ul,u2,...,Um）. We give an upper bound for Castelnuovo-Mumford regularity of I by the bigsize of I. As a corollary, the projective dimension of I is bounded by the number w.展开更多
In this paper, we present a fast and fraction free procedure for computing the inertia of Bezout matrix and we can determine the numbers of different real roots and different pairs of conjugate complex roots of a pol...In this paper, we present a fast and fraction free procedure for computing the inertia of Bezout matrix and we can determine the numbers of different real roots and different pairs of conjugate complex roots of a polynomial equation with integer coefficients quickly based on this result.展开更多
The -B -free number is a generalization of the well-known squarefree numbers. The result that if θ】33/80, then the interval [x-xθ,x] must contain a B-free number for large x has been proved.
In this paper, we study the notion of chordality and cycles in clutters from a commutative algebraic point of view. The corresponding concept of chordality in commutative algebra is having a linear resolution. We main...In this paper, we study the notion of chordality and cycles in clutters from a commutative algebraic point of view. The corresponding concept of chordality in commutative algebra is having a linear resolution. We mainly consider the generalization of chordality proposed by Bigdeli et al. in 2017 and the concept of cycles introduced by Can- non and Faridi in 2013, and study their interrelations and algebraic interpretations. In particular, we investigate the relationship between chordality and having linear quotients in some classes of clutters. Also, we show that if e is a clutter such that （ ） is a vertex decomposable simplicial complex or I（ ） is squarefree stable, then is chordal.展开更多
We characterize pure lexsegment complexes which are Cohen-Macaulay in arbitrary codimension. More precisely, we prove that any lexsegment complex is Cohen- Macaulay if and only if it is pure and its 1-dimensional link...We characterize pure lexsegment complexes which are Cohen-Macaulay in arbitrary codimension. More precisely, we prove that any lexsegment complex is Cohen- Macaulay if and only if it is pure and its 1-dimensional links are connected, and that a lexsegment flag complex is Cohen-Macaulay if and only if it is pure and connected. We show that any non-Cohen-Macaulay lexsegment complex is a Buchsbaum complex if and only if it is a pure disconnected flag complex. For t≥2, a lexsegment complex is strictly Cohen-Macaulay in codimension t if and only if it is the join of a lexsegment pure discon- nected flag complex with a （t - 2）-dimensional simplex. When the Stanley-Reisner ideal of a pure lexsegment complex is not quadratic, the complex is Cohen-Macaulay if and only if it is Cohen-Macaulay in some codimension. Our results are based on a characterization of Cohen-Macaulay and Buchsbaum lexsegment complexes by Bonanzinga, Sorrenti and Terai.展开更多
文摘Let K be a field and let A = K[X1,...,Xn] be the polynomial ring in X1, ..., Xn with coefficients in K. In this paper we study the universal squarefree lexsegment ideals, and put our attention on their combinatorics computing some invariants. Moreover, we study the link between such a special class of squarefree lexsegment ideals and the so-called s-sequences.
文摘Let K be a field and let S = K[x1,...,xn] be a polynomial ring over K. Let F = ir=1 Sei be a finitely generated graded free S-module with basis {e1,..., er} in degrees f1,..., fr such that f1≤ f2 ~≤……≤ fr. We examine some classes of squarefree monomial submodules of F. Hence, we focalize our attention on the Betti table of such classes in order to analyze the behavior of their extremal Betti numbers.
文摘We compute the minimal primary decomposition for completely squarefree lexsegment ideals. We show that critical squarefree monomial ideals are sequentially Cohen- Macaulay. As an application, we give a complete characterization of the completely square- free lexsegment ideals which are sequentially Cohen-Macaulay and we also derive formulas for some homological invariants of this class of ideals.
基金This work was supported in part by the National Natural Science Foundation of China （Grant No. 11201326）, the Natural Science Foundation of Jiangsu Province （No. BK2011276）, and the Jiangsu Provincial Training Programs of Innovation and Entrepreneurship for Undergraduates.
文摘Let S = K[x1, x2,..., xn] be the polynomial ring in n variables over a field K, and let I be a squarefree monomial ideal minimally generated by the monomials ul,u2,...,Um. Let w be the smallest number t with the property that for all integers 1 ≤ i1 〈 i2 〈 … 〈 it ≤ m such that lcm（uil, ui2,..., uii） = lcm（ul,u2,...,Um）. We give an upper bound for Castelnuovo-Mumford regularity of I by the bigsize of I. As a corollary, the projective dimension of I is bounded by the number w.
文摘In this paper, we present a fast and fraction free procedure for computing the inertia of Bezout matrix and we can determine the numbers of different real roots and different pairs of conjugate complex roots of a polynomial equation with integer coefficients quickly based on this result.
文摘The -B -free number is a generalization of the well-known squarefree numbers. The result that if θ】33/80, then the interval [x-xθ,x] must contain a B-free number for large x has been proved.
文摘In this paper, we study the notion of chordality and cycles in clutters from a commutative algebraic point of view. The corresponding concept of chordality in commutative algebra is having a linear resolution. We mainly consider the generalization of chordality proposed by Bigdeli et al. in 2017 and the concept of cycles introduced by Can- non and Faridi in 2013, and study their interrelations and algebraic interpretations. In particular, we investigate the relationship between chordality and having linear quotients in some classes of clutters. Also, we show that if e is a clutter such that （ ） is a vertex decomposable simplicial complex or I（ ） is squarefree stable, then is chordal.
文摘We characterize pure lexsegment complexes which are Cohen-Macaulay in arbitrary codimension. More precisely, we prove that any lexsegment complex is Cohen- Macaulay if and only if it is pure and its 1-dimensional links are connected, and that a lexsegment flag complex is Cohen-Macaulay if and only if it is pure and connected. We show that any non-Cohen-Macaulay lexsegment complex is a Buchsbaum complex if and only if it is a pure disconnected flag complex. For t≥2, a lexsegment complex is strictly Cohen-Macaulay in codimension t if and only if it is the join of a lexsegment pure discon- nected flag complex with a （t - 2）-dimensional simplex. When the Stanley-Reisner ideal of a pure lexsegment complex is not quadratic, the complex is Cohen-Macaulay if and only if it is Cohen-Macaulay in some codimension. Our results are based on a characterization of Cohen-Macaulay and Buchsbaum lexsegment complexes by Bonanzinga, Sorrenti and Terai.
