On the arithmetical rank of an intersection of ideals

Arithmetical ranks of Stanley-Reisner ideals via linear algebra

We present some examples of squarefree monomial ideals whose arithmetical rank can be computed using linear algebraic considerations.

On the arithmetical rank of certain monomial ideals

We determine a new technique which allows the computation of the arithmetical rank of certain monomial ideals.

On the arithmetical rank of a special class of minimal varieties

We study the arithmetical ranks and the cohomological dimensions of an infinite class of Cohen-Macaulay varieties of minimal degree. Among these we find, on the one hand, infinitely many set-theoretic complete intersections, on the other hand examples where the arithmetical rank is arbitrarily greater than the codimension.

Arithmetical rank of lexsegment edge ideals

Let $I\subset S=K[x_1,...,x_n]$ be a lexsegment edge ideal or the Alexander dual of such an ideal. In both cases it turns out that the arithmetical rank of $I$ is equal to the projective dimension of $S/I.$

The arithmetical rank of a special class of monomial ideals

We give an affirmative answer to a question due to J. He and A. Van Tuyl, proving that the arithmetical rank of a special monomial ideal equals to the projective dimension of corresponding quotient module.

Cohomological dimension and arithmetical rank of some determinantal ideals

Let $M$ be a $(2 \times n)$ non-generic matrix of linear forms in a polynomial ring. For large classes of such matrices, we compute the cohomological dimension (cd) and the arithmetical rank (ara) of the ideal $I_2(M)$ generated by the $2$-minors of $M$. Over an algebraically closed field, any $(2 \times n)$-matrix of linear forms can be written in the Kronecker-Weierstrass normal form, as a concatenation of scroll, Jordan and nilpotent blocks. Bădescu and Valla computed $\mathrm{ara}(I_2(M))$ when $M$ is a concatenation of scroll blocks. In this case we compute $\mathrm{cd}(I_2(M))$ and exten…

Arithmetical rank of Cohen-Macaulay squarefree monomial ideals of height two

In this paper, we prove that a squarefree monomial ideal of height 2 whose quotient ring is Cohen-Macaulay is set-theoretic complete intersection.

Arithmetical ranks of Stanley-Reisner ideals of simplicial complexes with a cone

When a cone is added to a simplicial complex $Δ$ over one of its faces, we investigate the relation between the arithmetical ranks of the Stanley-Reisner ideals of the original simplicial complex and the new simplicial complex $Δ'$. In particular, we show that the arithmetical rank of the Stanley-Reisner ideal of $Δ'$ equals the projective dimension of the Stanley-Reisner ring of $Δ'$ if the corresponding equality holds for $Δ$.

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.

通过标记基发展Cohen-Macaulay、Gorenstein和完全交条件

Cohen-Macaulay, Gorenstein and complete intersection conditions by marked bases

本文通过标记基理论，开发了检测和构造Cohen-Macaulay、Gorenstein和完全交多项式理想的新计算方法，并证明了相关位置在Hilbert方案中的开放性。

Arithmetical rank of squarefree monomial ideals generated by five elements or with arithmetic degree four

Let $I$ be a squarefree monomial ideal of a polynomial ring $S$. In this paper, we prove that the arithmetical rank of $I$ is equal to the projective dimension of $S/I$ when one of the following conditions is satisfied: (1) $μ(I) \leq 5$; (2) $\arithdeg I \leq 4$.

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.

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.

The arithmetical rank of the edge ideals of cactus graphs

We prove that, for the edge ideal of a cactus graph, the arithmetical rank is bounded above by the sum of the number of cycles and the maximum height of its associated primes. The bound is sharp, but in many cases it can be improved. Moreover, we show that the edge ideal of a Cohen-Macaulay graph that contains exactly one cycle or is chordal or has no cycles of length 4 and 5 is a set-theoretic complete intersection.

Projections of cones and the arithmetical rank of toric varieties

Let $I_M$ and $I_N$ be defining ideals of toric varieties such that $I_M$ is a projection of $I_N$, i.e. $I_N \subseteq I_M$. We give necessary and sufficient conditions for the equality $I_M=rad(I_N+(f_1,...,f_s))$, where $f_1,...,f_s$ belong to $I_M$. Also a method for finding toric varieties which are set-theoretic complete intersection is given. Finally we apply our method in the computation of the arithmetical rank of certain toric varieties and provide the defining equations of the above toric varieties.

$p-$Ferrer diagram, $p-$linear ideals and arithmetical rank

In this paper we introduce $p-$Ferrer diagram, note that $1-$ Ferrer diagram are the usual Ferrer diagrams or Ferrer board, and corresponds to planar partitions. To any $p-$Ferrer diagram we associate a $p-$Ferrer ideal. We prove that $p-$Ferrer ideal have Castelnuovo mumford regularity $p+1$. We also study Betti numbers, minimal resolutions of $p-$Ferrer ideals. Every $p-$Ferrer ideal is $p-$joined ideals in a sense defined in a fortcoming paper \cite{m2}, which extends the notion of linearly joined ideals introduced and developped in the papers \cite{bm2}, \cite{bm4},\cite{eghp} and \cite{m1…

广义二项式边理想的算术秩与上同调维数

Arithmetical rank and cohomological dimension of generalized binomial edge ideals

本文研究连通简单图对应的广义二项式边理想，给出其上同调维数下界，刻画上同调完全交条件，并在多种情形下证明 $J_2(G)$ 的算术秩等于商环投射维数。

On ideals generated by monomials and one binomial

We determine, in a polynomial ring over a field, the arithmetical rank of certain ideals generated by a set of monomials and one binomial.

Arithmetical rank of the cyclic and bicyclic graphs

We show that for the edge ideals of the graphs consisting of one cycle or two cycles of any length connected through a vertex or a path, the arithmetical rank equals the projective dimension.

Some characterizations of strongly irreducible submodules in arithmetical and Noetherian modules

The purpose of the present paper is to prove some properties of the strongly irreducible submodules in the arithmetical and Noetherian modules over a commutative ring. The relationship among the families of strongly irreducible submodules, irreducible submodules, prime submodules and primal submodules is proved. Also, several new characterizations of the arithmetical modules are given. In the case when $R$ is Noetherian and $M$ is finitely generated, several characterizations of strongly irreducible submodules are included. Among other things, it is shown that when $N$ is a submodule of $M$ su…

Arithmetical rank of strings and cycles

Let $R$ be a polynomial ring over a field $K$. To a given squarefree monomial ideal $I \subset R$, one can associate a hypergraph $H(I)$. In this article, we prove that the arithmetical rank of $I$ is equal to the projective dimension of $R/I$ when $H(I)$ is a string or a cycle hypergraph.

A note on the edge ideals of Ferrers graphs

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

The minimal free resolution of fat almost complete intersections in $\mathbb{P}^1\times\mathbb{P}^1$

A current research theme is to compare symbolic powers of an ideal $I$ with the regular powers of $I$. In this paper, we focus on the case that $I=I_X$ is an ideal defining an almost complete intersection (ACI) sets of points $X$ in $\mathbb{P}^1\times\mathbb{P}^1$. In particular, we describe a minimal free bigraded resolution of a non arithmetically Cohen-Macaulay (also non homogeneus) set of fat points $\mathcal Z$ whose support is an ACI. We call $\mathcal Z$ a fat ACI. We also show that its symbolic and ordinary powers are equal, i.e, $I_{\mathcal Z}^{(m)}=I_{\mathcal Z}^{m}$ for any $m\ge…

Complete Intersection Lattice Ideals

In this paper we completely characterize lattice ideals that are complete intersections or equivalently complete intersections finitely generated semigroups of $\bz^n\oplus T$ with no invertible elements, where $T$ is a finite abelian group. We also characterize the lattice ideals that are set-theoretic complete intersections on binomials.

完全交理想残差交的算术秩

The arithmetic rank of the residual intersections of a complete intersection ideal

研究完全交理想残差交的算术秩，确定其在任意特征下的上界，并给出其集合理论生成元的显式描述。

Complete intersections in toric ideals

We present examples which show that in dimension higher than one or codimension higher than two, there exist toric ideals I_A such that no binomial ideal contained in I_A and of the same dimension is a complete intersection. This result has important implications in sparse elimination theory and in the study of the Horn system of partial differential equations.

Gröbner scheme in the Hilbert scheme and complete intersection monomial ideals

Let $k$ be a commutative ring and $S=k[x_0, \ldots, x_n]$ be a polynomial ring over $k$ with a monomial order. For any monomial ideal $J$, there exists an affine $k$-scheme of finite type, called Gröbner scheme, which parameterizes all homogeneous reduced Gröbner bases in $S$ whose initial ideal is $J$. Here we functorially show that the Gröbner scheme is a locally closed subscheme of the Hilbert scheme if $J$ is a saturated ideal. In the process, we also show that the Gröbner scheme consists of complete intersections if $J$ defines a complete intersection.

Monomial ideals, almost complete intersections and the Weak Lefschetz Property

Many algebras are expected to have the Weak Lefschetz property though this is often very difficult to establish. We illustrate the subtlety of the problem by studying monomial and some closely related ideals. Our results exemplify the intriguing dependence of the property on the characteristic of the ground field, and on arithmetic properties of the exponent vectors of the monomials.

Residual Intersections of $2\times n$ Determinantal Ideals

Schemes defined by residual intersections have been extensively studied in the case when they are Cohen-Macaulay, but this is a very restrictive condition. In this paper we make the first study of a class of natural examples far from satisfying this condition, the rank 1 loci of generic $2\times n$ matrices. Here we compute their depths and many other properties. These computations require a number of novel tools.

Residual Intersections are Koszul-Fitting ideals

One describes generators of disguised residual intersections in any commutative Noetherian rings. It is shown that, over Cohen-Macaulay rings, the disguised residual intersections and algebraic residual intersections are the same, for ideals with sliding depth. This coincidence provides structural results for algebraic residual intersections in quite general setting. It is shown how the DG-algebra structure of Koszul homologies affects the determination of generators of residual intersections. In the midway it is shown that the Buchsbaum-Eisenbud family of complexes can be derived from the Kos…

Bernstein-Sato 理想的交结构

The Intersection Structure of Bernstein-Sato Ideals

本文利用对数 D 模与 Gröbner 基证明 Bernstein-Sato 理想具有对称交性质，回答 Budur 的问题，并据此给出多元多项式整数次幂的 Bernstein-Sato 多项式公式。

Monomial ideals and the Gorenstein liaison class of a complete intersection

It is well known that for a subscheme $V$ in ${\mathbb P}^{n}$ of codimension two, the conditions (1) $V$ is ACM, and (2) $V$ is "licci" (i.e. $V$ is in the liaison class of a complete intersection) are equivalent. In higher codimension, (2) implies (1) but the converse is false. For Gorenstein liaison the analog of (2) is: $(2')$ $V$ is "glicci" (i.e. $V$ is in the Gorenstein liaison class of a complete intersection). It remains true that $(2')$ implies (1) but now the converse is an important open question. Previously the authors described a mechanism for lifting monomial ideals to reduced u…

Powers of generic ideals and the weak Lefschetz property for powers of some monomial complete intersections

Given an ideal $I=(f_1,\ldots,f_r)$ in $\mathbb C[x_1,\ldots,x_n]$ generated by forms of degree $d$, and an integer $k>1$, how large can the ideal $I^k$ be, i.e., how small can the Hilbert function of $\mathbb C[x_1,\ldots,x_n]/I^k$ be? If $r\le n$ the smallest Hilbert function is achieved by any complete intersection, but for $r>n$, the question is in general very hard to answer. We study the problem for $r=n+1$, where the result is known for $k=1$. We also study a closely related problem, the Weak Lefschetz property, for $S/I^k$, where $I$ is the ideal generated by the $d$'th powers of the v…

某些完全交形式的Waring秩

Waring rank of certain complete intersection forms

本文计算某些完全交形式的Waring秩，作为应用得到零化子为完全交理想的二项式及不同变量集上二元形式乘积的Waring秩，丰富了相关代数不变量的研究。

On Complete Intersection toric ideals of graphs

We characterize the graphs $G$ for which their toric ideals $I_G$ are complete intersections. In particular we prove that for a connected graph $G$ such that $I_G$ is complete intersection all of its blocks are bipartite except of at most two. We prove that toric ideals of graphs which are complete intersections are circuit ideals. The generators of the toric ideal correspond to even cycles of $G$ except of at most one generator, which corresponds to two edge disjoint odd cycles joint at a vertex or with a path. We prove that the blocks of the graph satisfy the odd cycle condition. Finally we …

Commutative rings in which every finitely generated ideal is quasi-projective

This paper studies the multiplicative ideal structure of commutative rings in which every finitely generated ideal is quasi-projective. Section 2 provides some preliminaries on quasi-projective modules over commutative rings. Section 3 investigates the correlation with well-known Prufer conditions; namely, we prove that this class of rings stands strictly between the two classes of arithmetical rings and Gaussian rings. Thereby, we generalize Osofsky's theorem on the weak global dimension of arithmetical rings and partially resolve Bazzoni-Glaz's related conjecture on Gaussian rings. We also e…

Residual Intersections and Linear Powers

If I is an ideal in a Gorenstein ring S and S/I is Cohen-Macaulay, then the same is true for any linked ideal I'. However, such statements hold for residual intersections of higher codimension only under very restrictive hypotheses, not satisfied even by ideals as simple as the ideal L_n of minors of a generic 2 x n matrix when n>3. In this paper we initiate the study of a different sort of Cohen-Macaulay property that holds for certain general residual intersections of the maximal (interesting) codimension, one less than the analytic spread of I. For example, we prove that if K is the residua…

Certain minimal varieties are set-theoretic complete intersections

We present a class of homogeneous ideals which are generated by monomials and binomials of degree two and are set-theoretic complete intersections. This class includes certain reducible varieties of minimal degree and, in particular, the presentation ideals of the fiber cone algebras of monomial varieties of codimension two.

Topological aspects of irredundant intersections of ideals and valuation rings

An intersection of sets $A = \bigcap_{i \in I}B_i$ is irredundant if no $B_i$ can be omitted from this intersection. We develop a topological approach to irredundance by introducing a notion of a spectral representation, a spectral space whose members are sets that intersect to a given set $A$ and whose topology encodes set membership. We define a notion of a minimal representation and show that for such representations, irredundance is a topological property. We apply this approach to intersections of valuation rings and ideals. In the former case we focus on Krull-like domains and Prüfer $v$…

关于某些完全交形式的幂次和的多样性

On the variety of sum of powers of certain complete intersection forms

本文研究完全交形式，证明其极小反极理想为完全交，且VSP(F)不可约并计算其维数。

有限域上退化环面上的完全交消失理想

Complete intersection vanishing ideals on degenerate tori over finite fields

研究有限域上退化环面消失理想的完全交性质，建立其与数值半群环面理想的对应，并给出次数和正则指数的公式。

Commutative rings whose finitely generated ideals are quasi-flat

A definition of quasi-flat left module is proposed and it is shown that any left module which is either quasi-projective or flat is quasi-flat. A characterization of local commutative rings for which each ideal is quasi-flat (resp. quasi-projective) is given. It is also proven that each commutative ring R whose finitely generated ideals are quasi-flat is of $λ$-dimension $\le$ 3, and this dimension $\le$ 2 if R is local. This extends a former result about the class of arithmetical rings. Moreover, if R has a unique minimal prime ideal then its finitely generated ideals are quasi-projective if …

Cohen-Macaulay residual intersections and their Castelnuovo-Mumford Regularity

In this article we study the structure of residual intersections via constructing a finite complex which is acyclic under some sliding depth conditions on the cycles of the Koszul complex. This complex provides information on an ideal which coincides with the residual intersection in the case of geometric residual intersection; and is closely related to it in general. A new success obtained through studying such a complex is to prove the Cohen-Macaulayness of residual intersections of a wide class of ideals. For example we show that, in a Cohen-Macaulay local ring, any geometric residual inter…

The Limiting Polytope of the Generic Initial System of a Complete Intersection

Consider a complete intersection I of type (d_1,..., d_r) in a polynomial ring over a field of characteristic 0. We study the graded system of ideals {gin(I^n)}_n obtained by taking the reverse lexicographic generic initial ideals of the powers of I and describe its asymptotic behavior. This behavior is nicely captured by the limiting polytope which is shown to depend only on the type of the complete intersection.

Intersection algebras for principal monomial ideals in polynomial rings

The properties of the intersection algebra of two principal monomial ideals in a polynomial ring are investigated in detail. Results are obtained regarding the Hilbert series and the canonical ideal of the intersection algebra using methods from the theory of diophantine linear equations with integer coefficients.

Generating Residual Intersections of Determinantal Ideals

If $I$ is a perfect ideal in a local Cohen-Macaulay ring, the generators of ideals linked to $I$ are well understood. However, the generators of the residual intersections of $I$ have only been computed in a few special cases. In this paper, we show that the $n$-residual intersections of determinantal ideals of generic $2\times n$ matrices are sums of links.

Transversal Intersection of Monomial Ideals

In this paper we prove conditions for transversal intersection of monomial ideals and derive a simplicial characterization of this phenomenon.

The Stanley-Reisner ideals of polygons as set-theoretic complete intersections

We show that the Stanley-Reisner ideal of the one-dimensional simplicial complex whose diagram is an $n$-gon is always a set-theoretic complete intersection in any positive characteristic.

二项式理想与格理想中的完全交集

Complete intersections in binomial and lattice ideals

本文针对一维齐次格理想族，建立了完全交集的代数与几何判别准则，并证明了正特征下所有此类理想均为二项式集合论完全交集，零特征下二项式集合论完全交集必为完全交集。

单项完全交理想的商的Stanley深度

Stanley depth of quotient of monomial complete intersection ideals

本文计算了完全交单项式理想之商在特殊情形下的Stanley深度，给出了一般情形下的精确界，并证明了该情形满足Stanley猜想。

The Generic Initial Ideals of Powers of a 2-Complete Intersection

We compute the reverse lexicographic generic initial ideals of the powers of a 2-complete intersection ideal I. In particular, we give six algorithms to compute these generic initial ideals, the choice of which depends on the power and on the relative degrees of the minimal generators of I.

Lefschetz properties for complete intersection ideals generated by products of linear forms

In this paper, we study the strong Lefschetz property of artinian complete intersection ideals generated by products of linear forms. We prove the strong Lefschetz property for a class of such ideals with binomial generators.

Stanley conjecture on intersections of four monomial prime ideals

We show that the Stanley's Conjecture holds for an intersection of four monomial prime ideals of a polynomial algebra $S$ over a field and for an arbitrary intersection of monomial prime ideals $(P_i)_{i\in [s]}$ of $S$ such that $P_i\not\subset Σ_{1=j\not =i}^s P_j$ for all $i\in [s]$.

Stanley depth of complete intersection monomial ideals

We compute the Stanley depth of irreducible monomial ideals and we show that the Stanley depth of a monomial complete intersection ideal is the same as the Stanley depth of it's radical. Also, we give some bounds for the Stanley depth of a monomial complete intersection ideal.