On the linear strand of an edge ideal

素数理想二次线性串

Quadratic linear strands of prime ideals

研究素数理想在标准 graded多项式环中的解的二次串的精确估计，证明高度为h的理想最多含h²个二次极小生成元，且存在由h²个二次式生成的理想。

Binomial edge ideals with pure resolutions

We characterize all graphs whose binomial edge ideals have pure resolutions. Moreover, we introduce a new switching of graphs which does not change some algebraic invariants of graphs, and using this, we study the linear strand of the binomial edge ideals for some classes of graphs. Also, we pose a conjecture on the linear strand of such ideals for every graph.

Linear strands of edge ideals of multipartite uniform clutters

We construct the first linear strand of the minimal free resolutions of edge ideals of $d$-partite $d$-uniform clutters. We show that the first linear strand is supported on a relative simplicial complex. In the case that the edge ideals of such clutters have linear resolutions, we give an explicit and surprisingly simple description of their minimal free resolutions, generalizing the known resolutions for edge ideals of Ferrers graphs and hypergraphs and co-letterplace ideals. As an application, we show that the Lyubeznik numbers that appear on the last column of the Lyubeznik table of the co…

Lyubeznik numbers of local rings and linear strands of graded ideals

In this work we introduce a new set of invariants associated to the linear strands of a minimal free resolution of a $\mathbb{Z}$-graded ideal $I\subseteq R=\Bbbk[x_1, \ldots, x_n]$. We also prove that these invariants satisfy some properties analogous to those of Lyubeznik numbers of local rings. In particular, they satisfy a consecutiveness property that we prove first for Lyubeznik numbers. For the case of squarefree monomial ideals we get more insight on the relation between Lyubeznik numbers and the linear strands of their associated Alexander dual ideals. Finally, we prove that Lyubeznik…

Jump Sequences of Edge Ideals

Given an edge ideal of graph G, we show that if the first nonlinear strand in the resolution of $I_G$ is zero until homological stage $a_1$, then the next nonlinear strand in the resolution is zero until homological stage $2a_1$. Additionally, we define a sequence, called a \emph{jump sequence}, characterizing the highest degrees of the free resolution of the edge ideal of G via the lower edge of the Betti diagrams of $I_G$. These sequences strongly characterize topological properties of the underlying Stanley-Reisner complexes of edge ideals, and provide general conditions on construction of …

Rigidity of linear strands and generic initial ideals

Let $K$ be a field, $S$ a polynomial ring and $E$ an exterior algebra over $K$, both in a finite set of variables. We study rigidity properties of the graded Betti numbers of graded ideals in $S$ and $E$ when passing to their generic initial ideals. First, we prove that if the graded Betti numbers $β_{ii+k}^S(S/I)=β_{ii+k}^S(S/\Gin(I))$ for some $i>1$ and $k \geq 0$, then $β_{qq+k}^S(S/I)= β_{qq+k}^S(S/\Gin(I))$ for all $q \geq i$, where $I\subset S$ is a graded ideal. Second, we show that if $β_{ii+k}^E(E/I)= β_{ii+k}^E(E/\Gin(I))$ for some $i>1$ and $k \geq 0$, then $β_{qq+k}^E(E/I)= β_{qq+k…

On the binomial edge ideals of proper interval graphs

We prove several cases of the Betti number conjecture for the binomial edge ideal $J_G$ of a proper interval graph $G$ (also known as closed graph). Namely, we show that this conjecture is true for the linear strand of $J_G$, and true in general for any proper interval graph $G$ such that the regularity of $S/J_G$ equals two.

Path ideals of rooted trees and their graded Betti numbers

Let $Γ$ be a rooted tree and let $t$ be a positive integer. We study algebraic invariants and properties of the path ideal generated by monomial corresponding to paths of length $(t-1)$ in $Γ$. In particular, we give a recursive formula to compute the graded Betti numbers, a general bound for the regularity, an explicit computation of the linear strand, and we characterize when this path ideal has a linear resolution.

Restricting linear syzygies: algebra and geometry

In this paper we derive geometric consequences from the presence of a long strand of linear syzygies in the minimal free resolution of a closed scheme in projective space whose homogeneous ideal is generated by quadrics. These consequences are given in terms of intersections with arbitrary linear subspaces. We use our results to bound homological invariants of some well-known projective varieties, to give a combinatorial characterization of quadratic monomial ideals with a long strand of linear syzygies, etc

Certain Homological Invariants of Bipartite Kneser Graphs

In this paper, we obtain a combinatorial formula for computing the Betti numbers in the linear strand of edge ideals of bipartite Kneser graphs. We deduce lower and upper bounds for regularity of powers of edge ideals of these graphs in terms of associated combinatorial data and show that the lower bound is attained in some cases. Also, we obtain bounds on the projective dimension of edge ideals of these graphs in terms of combinatorial data.

Cohen-Macaulay edge-weighted edge ideals of very well-covered graphs

We characterize unmixed and Cohen-Macaulay edge-weighted edge ideals of very well-covered graphs. We also provide examples of oriented graphs which have unmixed and non-Cohen-Macaulay vertex-weighted edge ideals, while the edge ideal of their underlying graph is Cohen-Macaulay. This disproves a conjecture posed by Pitones, Reyes and Toledo.

Cohen-Macaulay binomial edge ideals

We study the depth of classes of binomial edge ideals and classify all closed graphs whose binomial edge ideal is Cohen--Macaulay.

On the binomial edge ideals of block graphs

We find a class of block graphs whose binomial edge ideals have minimal regularity. As a consequence, we characterize the trees whose binomial edge ideals have minimal regularity. Also, we show that the binomial edge ideal of a block graph has the same depth as its initial ideal.

Licci binomial edge ideals

We give a complete characterization of graphs whose binomial edge ideal is licci. An important tool is a new general upper bound for the regularity of binomial edge ideals.

Cohen-Macaulay binomial edge ideals of cactus graphs

We classify the Cohen-Macaulay binomial edge ideals of cactus and bicyclic graphs.

Regularity, Depth and Arithmetic Rank of Bipartite Edge Ideals

We study minimal free resolutions of edge ideals of bipartite graphs. We associate a directed graph to a bipartite graph whose edge ideal is unmixed, and give expressions for the regularity and the depth of the edge ideal in terms of invariants of the directed graph. For some classes of unmixed edge ideals, we show that the arithmetic rank of the ideal equals projective dimension of its quotient.

A note on the edge ideals of Ferrers graphs

We determine the arithmetical rank of every edge ideal of a Ferrers graph.

The v-number of edge ideals

The aim of this work is to study the v-number of edge ideals of clutters and graphs. We relate the v-number with the regularity of edge ideals and study the combinatorial structure of the graphs whose edge ideals have their second symbolic power Cohen-Macaulay.

图的幂的边理想的正则性

Regularity of edge ideals of powers of graphs

本文研究图的幂的边理想的正则性，证明了森林的幂的边理想正则性弱递减，并计算了圈的幂的边理想正则性。

Cohen-Macaulay binomial edge ideals of small deviation

We classify all binomial edge ideals that are complete intersection and Cohen-Macaulay almost complete intersection. We also describe an algorithm and provide an implementation to compute primary decomposition of binomial edge ideals.

Powers of binomial edge ideals with quadratic Gröbner bases

We study powers of binomial edge ideals associated with closed and block graphs.

（广义）二项式边理想及其正则性

(Generalized) binomial edge ideals and their regularity

本文综述二项式边理想及广义二项式边理想的Castelnuovo-Mumford正则性研究进展，并将已知上界推广至广义情形。

Gorenstein Binomial Edge Ideals

We classify connected graphs $G$ whose binomial edge ideal is Gorenstein. The proof uses methods in prime characteristic.

On the arithmetical rank of the edge ideals of forests

We show that for the edge ideals of a certain class of forests, the arithmetical rank equals the projective dimension.

Powers of edge ideals

We compute the Betti numbers for all the powers of initial and final lexsegment edge ideals. For the powers of the edge ideal of an anti-$d-$path, we prove that they have linear quotients and we characterize the normally torsion-free ideals. We determine a class of non-squarefree ideals, arising from some particular graphs, which are normally torsion-free.

Gotzmann Edge Ideals

Let P = k[x_1, ..., x_n] be the polynomial ring in n variables. A homogeneous ideal I of P generated in degree d is called Gotzmann if it has the smallest possible Hilbert function out of all homogeneous ideals with the same dimension in degree d. The edge ideal of a simple graph G on vertices x_1, ..., x_n is the quadratic square-free monomial ideal generated by all x_i x_j where {x_i,x_j} is an edge of G. The only edge ideals that are Gotzmann are those edge ideals corresponding to star graphs.

Hankel edge ideals of trees and (semi-)Hamiltonian graphs

In this paper, we study the Hankel edge ideals of graphs. We determine the minimal prime ideals of the Hankel edge ideal of labeled Hamiltonian and semi-Hamiltonian graphs, and we investigate radicality, being a complete intersection, almost complete intersection and set theoretic complete intersection for such graphs. We also consider the Hankel edge ideal of trees with a natural labeling, called rooted labeling. We characterize such trees whose Hankel edge ideal is a complete intersection, and moreover, we determine those whose initial ideal with respect to the reverse lexicographic order sa…

Edge ideals of clique clutters of comparability graphs and the normality of monomial ideals

Let (P,<) be a finite poset and let G be its comparability graph. If cl(G) is the clutter of maximal cliques of G, we prove that cl(G) satisfies the max-flow min-cut property and that its edge ideal is normally torsion free. We prove that edge ideals of complete admissible uniform clutters are normally torsion free. The normality of a monomial ideal is expressed in terms of blocking polyhedra and the integer decomposition property. For edge ideals of clutters this property completely determine their normality

补边理想

Complementary edge ideals

本文提出图的补边理想概念，并研究其代数性质与不变量。

Extremal Betti numbers of some classes of binomial edge ideals

Let $G$ be a cycle or a complete bipartite graph. We show that the binomial edge ideal $J_{G}$ and its initial ideal with respect to the lexicographic order have the same extremal Betti number.

Regularity stabilization for the powers of graded m-primary ideals

This Note provides first a generalization of the stabilization result of Eisenbud and Ulrich for the regularity of powers of a m-primary ideal to the case of ideals that are not generated in a single degree. We then partially extend our previous results expressing this stabilization degree in term of the regularity of a specific graded strand of the Rees ring : The natural extension of the statement holds at least if the stabilization index or the regularity is greater than the number of variables. In any case a precise comparison is given.

Regularity of Binomial Edge Ideals of Certain Block Graphs

We obtain an improved lower bound for the regularity of the binomial edge ideals of trees. We prove an upper bound for the regularity of the binomial edge ideals of certain subclass of block-graphs. As a consequence we obtain sharp upper and lower bounds for the regularity of binomial edge ideals of a class of trees called lobsters. We also obtain precise expressions for the regularities of binomial edge ideals of certain classes of trees and block graphs.

Binomial edge ideals of weakly closed graphs

Closed graphs have been characterized by Herzog et al. as the graphs whose binomial edge ideals have a quadratic Gröbner basis with respect to a diagonal term order. In this paper, we focus on a generalization of closed graphs, namely weakly-closed graphs (or co-comparability graphs). Build on some results about Knutson ideals of generic matrices, we characterize weakly closed graphs as the only graphs whose binomial edge ideals are Knutson ideals for a certain polynomial $f$. In doing so, we re-prove Matsuda's theorem about the F-purity of binomial edge ideals of weakly closed graphs in posit…

关于二项边理想的符号$F$-分裂性

On the symbolic $F$-splitness of binomial edge ideals

本文研究了二项边理想族的符号$F$-分裂性及其符号吹胀代数的强$F$-正则性，利用Fedder类准则和相关图的组合性质对上述情形进行了探讨。

Sequentially Cohen-Macaulay binomial edge ideals of closed graphs

In this paper we provide a full combinatorial characterization of sequentially Cohen-Macaulay binomial edge ideals of closed graphs. In addition, we show that a binomial edge ideal of a closed graph is approximately Cohen-Macaulay if and only if it is almost Cohen-Macaulay.

Stability of Associated Primes and Depth of Integral Closures of Powers of Edge Ideals

In this paper, we study associated primes and depth of integral closures of powers of edge ideals. We provide sharp bounds on how big of powers for which the set of associated primes and the depth of integral closures of powers of edge ideals are stable.

On the extremal Betti numbers of binomial edge ideals of block graphs

We compute one of the distinguished extremal Betti number of the binomial edge ideal of a block graph, and classify all block graphs admitting precisely one extremal Betti number.

Regularity of edge ideal of a graph

In this paper, we introduce some reduction processes on graphs which preserve the regularity of related edge ideals. As a consequence, an alternative proof for the theorem of R. Fröberg on linearity of resolution of edge ideal of graphs is given.

The arithmetical rank of the edge ideals of graphs with whiskers

We consider the edge ideals of large classes of graphs with whiskers and for these ideals we prove that the arithmetical rank is equal to the big height. Then we extend these results to other classes of squarefree monomial ideals, generated in any degree, proving that the same equality holds.

图的边理想的正规Rees代数的正则性

Regularity of normal Rees algebras of edge ideals of graphs

本研究针对图的边理想的正规Rees代数，分类了所有满足代数正规且正则性与图的匹配数相等的图，完善了交换代数与图论交叉领域的相关结论。

Koszul homology of quotients by edge ideals

We show that the Koszul homology algebra of a quotient by the edge ideal of a forest is generated by the lowest linear strand. This provides a large class of Koszul algebras whose Koszul homology algebras satisfy this property. We obtain this result by constructing the minimal graded free resolution of a quotient by such an edge ideal via the so called iterated mapping cone construction and using the explicit bases of Koszul homology given by Herzog and Maleki. Using these methods we also recover a result of Roth and Van Tuyl on the graded Betti numbers of quotients of edge ideals of trees.

Some Cohen-Macaulay and unmixed binomial edge ideals

We study unmixed and Cohen-Macaulay properties of the binomial edge ideal of some classes of graphs. We compute the depth of the binomial edge ideal of a generalized block graph. We also characterize all generalized block graphs whose binomial edge ideals are Cohen-Macaulay and unmixed. So that we generalize the results of Ene, Herzog and Hibi on block graphs. Moreover, we study unmixedness and Cohen-Macaulayness of the binomial edge ideal of some graph products such as the join and corona of two graphs with respect to the original graphs'.

Lower bounds for the depth of second power of edge ideals

Assume that $G$ is a graph with edge ideal $I(G)$. We provide sharp lower bounds for the depth of $I(G)^2$ in terms of the star packing number of $G$.

The Regularity of Powers of Edge Ideals

In this paper we prove the existence of a special order on the set of minimal monomial generators of powers of edge ideals of arbitrary graphs. Using this order we find new upper bounds on the regularity of powers of edge ideals of graphs whose complement does not have any induced four cycle.

Non-vanishing of Betti numbers of edge ideals and complete bipartite subgraphs

Given a finite simple graph one can associate the edge ideal. In this paper we prove that a graded Betti number of the edge ideal does not vanish if the original graph contains a set of complete bipartite subgraphs with some conditions. Also we give a combinatorial description for the projective dimension of the edge ideals of unmixed bipartite graphs.

Bouquets, vertex covers and edge ideals

We give a new combinatorial characterization of the big height of a squarefree monomial ideal leading to a new bound for the projective dimension of a monomial ideal.

Koszul 双项边理想

Koszul Binomial Edge Ideals

本文证明图定义Koszul双项边理想当且仅当图是强弦图且无爪图。

单圈图的d-序列（奇偶）二项式边缘理想的幂的正则度

Regularity of powers of d-sequence (parity) binomial edge ideals of unicycle graphs

本文分类了单圈图中边缘二项式构成d-序列的图，并研究其（奇偶）二项式边缘理想的幂的正则度。

D-序列边二项式与树的二项式边理想的幂的正则性

D-Sequence Edge Binomials, and Regularity of Powers of Binomial Edge Ideals of Trees

本文以图的度序列为依据，给出了树的边二项式构成 $d$-序列的充要条件，并研究了由 $d$-序列边二项式生成的树的二项式边理想幂的正则性。

Matchings and squarefree powers of edge ideals

Squarefree powers of edge ideals are intimately related to matchings of the underlying graph. In this paper we give bounds for the regularity of squarefree powers of edge ideals, and we consider the question of when such powers are linearly related or have linear resolution. We also consider the so-called squarefree Ratliff property.

Binomial edge ideals of regularity $3$

Let $J_G$ be the binomial edge ideal of a graph $G$. We characterize all graphs whose binomial edge ideals, as well as their initial ideals, have regularity $3$. Consequently we characterize all graphs $G$ such that $J_G$ is extremal Gorenstein. Indeed, these characterizations are consequences of an explicit formula we obtain for the regularity of the binomial edge ideal of the join product of two graphs. Finally, by using our regularity formula, we discuss some open problems in the literature. In particular we disprove a conjecture in \cite{CDI} on the regularity of weakly closed graphs.

A proof for a conjecture on the regularity of binomial edge ideals

In this paper we introduce the concept of clique disjoint edge sets in graphs. Then, for a graph $G$, we define the invariant $η(G)$ as the maximum size of a clique disjoint edge set in $G$. We show that the regularity of the binomial edge ideal of $G$ is bounded above by $η(G)$. This, in particular, settles a conjecture on the regularity of binomial edge ideals in full generality.

加权有向图边理想的同调不变量

Homological invariants of edge ideals of weighted oriented graphs

该研究确定了固定顶点数加权有向图边理想的深度、维数和正则性三元组，并计算了固定顶点数加权有向树及二部图边理想的贝蒂表大小。

The arithmetical rank of the edge ideals of graphs with pairwise disjoint cycles

We prove that, for the edge ideal of a graph whose cycles are pairwise vertex-disjoint, the arithmetical rank is bounded above by the sum of the number of cycles and the maximum height of its associated primes.