Ralf Fröberg, Lisa Nicklasson
We characterize all Gorenstein rings generated by strongly stable sets of monomials of degree two. We compute their Hilbert series in several cases, which also provides an answer to a question by Migliore and Nagel.
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We extend some results on almost Gorenstein affine monomial curves to the nearly Gorenstein case. In particular, we prove that the Cohen-Macaulay type of a nearly Gorenstein monomial curve in $\mathbb{A}^4$ is at most $3$, answering a question of Stamate in this particular case. Moreover, we prove that, if $\mathcal C$ is a nearly Gorenstein affine monomial curve which is not Gorenstein and $n_1, \dots, n_ν$ are the minimal generators of the associated numerical semigroup, the elements of $\{n_1, \dots, \widehat{n_i}, \dots, n_ν\}$ are relatively coprime for every $i$.
Nearly Gorenstein projective monomial curves of small codimension
本文研究小余维数情形下的近Gorenstein射影单项曲线，完整刻画了余维数为2和3的这类曲线的结构与分类。
We prove that the Cohen-Macaulay type of an almost Gorenstein monomial curve $\mathcal C \subseteq \mathbb{A}^4$ is at most $3$, and make some considerations on the general case.
We study the minimal free resolution of the tangent cone of Gorenstein monomial curves in affine 4-space. We give the explicit minimal free resolution of the tangent cone of non-complete intersection Gorenstein monomial curve whose tangent cone has five minimal generators and show that the possible Betti sequences are $(1,5,6,2)$ and $(1,5,5,1)$. Also, we compute the Hilbert function of the tangent cone of these families as a result.
Let $k$ be an arbitrary field. In this note, we show that if a sequence of relatively prime positive integers ${\bf a}=(a_1,a_2,a_3,a_4)$ defines a Gorenstein non complete intersection monomial curve ${\mathcal C}({\bf a})$ in ${\mathbb A}_k^4$, then there exist two vectors ${\bf u}$ and ${\bf v}$ such that ${\mathcal C}({\bf a}+t{\bf u})$ and ${\mathcal C}({\bf a}+t{\bf v})$ are also Gorenstein non complete intersection affine monomial curves for almost all $t\geq 0$.
We prove that the Cohen-Macaulay type of an almost Gorenstein monomial curve $\mathcal{C} \subseteq \mathbb{A}^5$ is bounded.
The aim of the article is to study the Betti numbers of the tangent cone of Gorenstein monomial curves in affine 4-space. If $C_S$ is a non-complete intersection Gorenstein monomial curve whose tangent cone is Cohen-Macaulay, we show that the possible Betti sequences are (1,5,5,1), (1,5,6,2) and (1,6,8,3).
Cohen-Macaulayness of associated graded rings of Gorenstein monomial curves
本文研究 4 维空间中 Gorenstein 非完全交单项式曲线的切锥 Cohen-Macaulay 性，利用定义理想的极小生成元集给出判定准则，并刻画了相应理想极小生成元个数的可能取值。
Let $C$ be a Gorenstein non complete intersection monomial curve in the 4-dimensional affine space. In this paper we study the minimal number of generators of the tangent cone of $C$. Special attention will be paid to the case where $C$ has Cohen-Macaulay tangent cone at the origin.
In this paper, we consider monomial curves in ${\mathbb A}_k^3$ parameterized by $t \rightarrow (t^{2q +1}, t^{2q +1 + m}, t^{2q +1 +2 m})$ where $gcd( 2q+1,m)=1$. The symbolic blowup algebras of these monomial curves is Gorenstein (\cite{goto-nis-shim}, \cite{goto-nis-shim-2}). We give a simple proof for the the Gorenstein property for the symbolic blowup algebras of these curves.
We introduce a general technique for decomposing monomial algebras which we use to study the Lefschetz properties. We apply our technique to various classes of algebras, including monomial almost complete intersections and Gorenstein algebras. In particular, we prove that Gorenstein codimension three algebras arising from numerical semigroups have the strong Lefschetz property. We also study the reverse of the splitting operation -- a gluing operation -- which gives a way to construct monomial algebras with the Lefschetz properties.
On posets, monomial ideals, Gorenstein ideals and their combinatorics
本文从组合角度比较单项式理想的 socle 元素与 Macaulay 逆系统，建立相关偏序集的闭包性质，推导 Γ-分次环的代数命题及其组合推论，并对零维 Gorenstein 理想进行直接计算，揭示多项式环与局部环之间的关键差异。
In this article, applying the quasi-Gorenstein analogous of the Ulrich's deformation of certain Gorenstein rings we show that some homological conjectures, including the Monomial Conjecture, Big Cohen-Macaulay Algebra Conjecture as well as the Small Cohen-Macaulay Conjecture reduce to the excellent unique factorization domains. Some other reductions of the Monomial Conjecture are also proved. We, moreover, show that certain almost complete intersections adhere the Monomial Conjecture.
Monomial ideals and the Gorenstein liaison class of a complete intersection
众所周知，对于余维为2的${\mathbb P}^{n}$中的子方案$V$，条件（1）$V$是ACM，以及（2）$V$是“licci”（即$V$处于完整交集的联络类中）是等价的。在较高的余维中，（2）蕴涵（1），但反之则不成立。对于Gorenstein联络，（2）的类似物是：$(2')$ $V$是“glicci”（即$V$在完全交集的Gorenstein联络类中）。$(2')$仍然意味着（1），但现在反过来是一个重要的开放问题。以前，作者描述了一种机制，提高单项式理想减少工会的线性品种。我们在这里表明，如果单项理想是阿丁然后相应的工会是glicci。因此，任何出现在ACM方案中的希尔伯特函数实际上都出现在glicci方案中。如果我们限制为完整的交叉连接，则情况并非如此。我们还证明了任何科恩-麦考利-博雷尔固定单名理想都是glicci。因此，射影空间的所有ACM子概型在平坦变形下都是glicci.
We characterize when the monomial maximal ideal of a simplicial affine semigroup ring has a monomial minimal reduction. When this is the case, we study the Cohen-Macaulay and Gorenstein properties of the associated graded ring and provide several bounds for the reduction number with respect to the monomial minimal reduction.
Koszulness of Gorenstein quadratic algebras of small socle degree is studied. In this note, we construct non-Koszul Gorenstein quadratic toric ring such that its socle degree is more than 3 by using stable set polytopes.
On the initial ideal of a generic artinian Gorenstein algebra
本文研究一般阿廷戈伦斯坦代数的初始理想，证明一般形式零化理想的初始理想由各次数最大单项式生成，并确定一类强稳定单项理想的总Betti数与相应初始理想一致。
A question of Conca, Rossi, and Valla asks whether every quadratic Gorenstein ring $R$ of regularity three is Koszul. In a previous paper, we use idealization to answer their question, proving that in nine or more variables there exist quadratic Gorenstein rings of regularity three which are not Koszul. In this paper, we study the analog of the Conca-Rossi-Valla question when the regularity of $R$ is four or more. Let $R$ be a quadratic Gorenstein ring having $\mathrm{codim}\, R = c$ and $\mathrm{reg}\, R = r \ge 4$. We prove that if $c = r+1$ then $R$ is always Koszul, and for every $c \geq r…
Roller Coaster Gorenstein algebras and Koszul algebras failing the weak Lefschetz property
受图论过山车定理启发，通过须状图定义的二次单项式代数的Nagata理想化构造，证明无约束希尔伯特级数的过山车Gorenstein代数存在，发现大量不满足弱Lefschetz性质的G-二次Gorenstein代数。
Let $R$ be a standard graded Gorenstein algebra over a field presented by quadrics. Conca, Rossi, and Valla have shown that such a ring is Koszul if $\mathrm{reg}\, R \leq 2$ or if $\mathrm{reg}\, = 3$ and $c= \mathrm{codim}\, R \leq 4$, and they ask whether this is true for $\mathrm{reg}\, R = 3$ in general. We determine sufficient conditions on a non-Koszul quadratic Cohen-Macaulay ring $R$ that guarantee the Nagata idealization $\tilde{R} = R \ltimes ω_R(-a-1)$ is a non-Koszul quadratic Gorenstein ring. We use this to negatively answer the question of Conca-Rossi-Valla, constructing non-Kos…
Let $k$ be a field of characteristic $0$. Using the method of idealization, we show that there is a non-Koszul, quadratic, Artinian, Gorenstein, standard graded $k$-algebra of regularity $3$ and codimension $8$, answering a question of Mastroeni, Schenck, and Stillman. We also show that this example is minimal in the sense that no other idealization that is non-Koszul, quadratic, Artinian, Gorenstein algebra, with regularity $3$ has smaller codimension. We also construct an infinite family of graded, quadratic, Artinian, Gorenstein algebras $A_m$, indexed by an integer $m \ge 2$, with the foll…
We study the deformation theory of quotients of polynomial rings by quadratic monomial ideals. More precisely we compute the first cotangent cohomology module of such rings. We also give a criterion for vanishing of second cotangent cohomology module.
In this article, by using the technique of gluing semigroups, we give infinitely many families of 1-dimensional local rings with non-decreasing Hilbert functions. More significantly, these are local rings whose associated graded rings are not necessarily Cohen-Macaulay. In this sense, we give an effective technique to construct large families of 1-dimensional Gorenstein local rings associated to monomial curves, which support Rossi's conjecture saying that every Gorenstein local ring has non-decreasing Hilbert function.
In [MMR], Michałek--Miró-Roig give a beautiful geometric characterization of Artinian quotients by ideals generated by quadratic or cubic monomials, such that the multiplication map by a general linear form fails to be injective in the first nontrivial degree. Their work was motivated by conjectures of Ilardi and Mezzetti-Miró-Roig-Ottaviani, connecting the failure to Laplace equations and classical results of Togliatti on osculating planes. We study quotients by quadratic monomial ideals, explaining failure of the Weak Lefschetz Property for some cases not covered by [MMR].
Signature invariants of monomial ideals
研究单项理想特征量的性质，证明其深度、正则度及Cohen-Macaulay/Gorenstein性质的等价性，并提供计算特征理想的方法。
Polarization and Gorenstein liaison
研究通过极化技术探讨G-联络构造，证明极化稳定Cohen-Macaulay单项式理想的Stanley-Reisner复形可顶点分解，并建立极化与G-联络的关系。
Gorenstein rings call the tune
Hochster的Monomial猜想和Canonical Element猜想分别可以追溯到30多年前。二十年它们涉及到所有的诺特交换局部环，并由它们的创始人以等价的特征证明了。由于海特曼最近的重要进展，现在已知它们对所有小于4维的环都具有混合特征。然而，其余的案件是这一领域最受保护的秘密之一。我们证明了这些图可以看作是关于同维数特殊特征的Gorenstein环及其模理论的陈述。在这次调查中，我们将以前一系列联合文章的相关结果串在一起。没有给出证明，但解释了它们背后的想法。特别是，我们宣传使用Auslander-Buchweitz方法。从而在已知的情形下得到许多关于Gorenstein环的不同的结果。在其余的，这是足以证明任何一个这些声明的Gorenstein环。
We show that for every positive integer R there exist monomial ideals generated in degree two, with linear syzygies, and regularity of the quotient equal to R. Such examples can not be found among Gorenstein ideals since the regularity of their quotients is at most four. We also show that for most monomial ideals generated in degree two and with linear syzygies the regularity grows at most doubly logarithmically in the number of variables.
Quasi-socle ideals in local rings with Gorenstein tangent cones
研究了具有Gorenstein切锥$\mathrm{G}(\mathfrak{m}) = \bigoplus_{n \geq 0}{\mathfrak{m}}^n/{\mathfrak{m}}^{n+1}$的Noether局部环$(A, \mathfrak{m})$中的拟socle理想，即$I= Q : \mathfrak{m}^q$形式的理想$I$，其中$q \geq 1$是整数，$Q$是$A$的参数理想，由$A$中元素的系统$x_1, x_2, ..., x_d$的单项式生成，使得$(x_1, x_2, ..., x_d)$是$\mathfrak{m}$的约化.回答了$I$何时是$Q$上的积分环以及分次环$\mathrm{G}(I) = \bigoplus_{n \geq 0}I^n/I^{n+1}$和$\mathrm{F}(I) = \bigoplus_{n \ge 0}I^n/\mathfrak{m} I^n$何时是Cohen-Macaulay环的问题.给出了$\mathrm{G} (I)$和$\mathcal{R} (I) = \bigoplus_{n \geq 0}I^n$是Gorenstein环的判别准则.
Bounded powers of edge ideals: Gorenstein toric rings
本文研究有限图边理想有界幂生成的 toric 环 $\mathcal{B}(\mathfrak{c},G)$ 的 Gorenstein 性质，该环在先前工作中已被证明是正规 Cohen--Macaulay 整环。
A study of a quadratic almost complete intersection ideal and its linked Gorenstein ideal
本文研究了二次几乎完全交理想及其链接的Gorenstein理想，计算了其Betti数，并揭示了相关环的socle结构和维度特性。
Considering finite extensions K[A] \subseteq K[B] of positive affine semigroup rings over a field K we have developed in [1] an algorithm to decompose K[B] as a direct sum of monomial ideals in K[A]. By computing the regularity of homogeneous semigroup rings from the decomposition we have confirmed the Eisenbud-Goto conjecture in a range of new cases not tractable by standard methods. Here we first illustrate this technique and its implementation in our Macaulay2 package MonomialAlgebras by computing the decomposition and the regularity step by step for an explicit example. We then focus on ri…
Castelnuovo-Mumford regularity is a measure of algebraic complexity of an ideal. Regularity of monomial ideals can be investigated combinatorially. We use a simple graph decomposition and results from structural graph theory to prove, improve and generalize many of the known bounds on regularity of quadratic square-free monomial ideals.
Simplicial Resolutions of the Quadratic Power of Monomial Ideals
本研究定义了支撑单项式理想二次幂消解的单纯复形及其子复形，得到投射维数与Betti数的更紧界，引入置换理想并证明其Betti数上界性质及对应单纯复形为Scarf复形。
Given a numerical semigroup ring $R=k[\![S]\!]$, an ideal $E$ of $S$ and an odd element $b \in S$, the numerical duplication $S \! \Join^b \! E$ is a numerical semigroup, whose associated ring $k[\![S \! \Join^b \! E]\!]$ shares many properties with the Nagata's idealization and the amalgamated duplication of $R$ along the monomial ideal $I=(t^e \mid e\in E)$. In this paper we study the associated graded ring of the numerical duplication characterizing when it is Cohen-Macaulay, Gorenstein or complete intersection. We also study when it is a homogeneous numerical semigroup, a property that is …
On Certain Gluing of semigroup rings and indispensable resolution of semigroup rings
本文通过粘合半群技术构造了无限多个具Cohen-Macaulay性质的射影闭包族和一维Gorenstein局部环族以支持Rossi问题，并研究仿射半群连接操作下的强不可或缺极小自由分解以支持Charalambous和Thoma问题。
The ring of differential operators on a monomial curve is a Hopf algebroid
本文证明数值半群代数对应的尖点曲线上，微分算子环构成余交换且余幂零的左Hopf代数胚，并在半群对称即曲线为Gorenstein时进一步成为具有对极的全Hopf代数胚。
We study some properties of a family of rings $R(I)_{a,b}$ that are obtained as quotients of the Rees algebra associated with a ring $R$ and an ideal $I$. In particular, we give a complete description of the spectrum of every member of the family and describe the localizations at a prime ideal. Consequently, we are able to characterize the Cohen-Macaulay and Gorenstein properties, generalizing known results stated in the local case. Moreover, we study when $R(I)_{a,b}$ is an integral domain, reduced, quasi-Gorenstein, or satisfies Serre's conditions.
We introduce the concept of quasi-linearity and prove it is necessary for a monomial ideal to have a linear resolution and identify all the quasi-linear quadratic monomial ideals. We define a strongly linear monomial for a monomial ideal $I$ and prove that if $\mathbf{u}$ is a strongly linear monomial over $I$ then $I$ has a linear resolution (resp: is quasi-linear) if and only if $I+\mathbf{u}\mathfrak{p}$ has a linear resolution (resp: is quasi-linear). Here $\mathfrak{p}$ is any monomial prime ideal.
Bounded powers of edge ideals: Gorenstein polytopes
本文研究了由有限图边理想的有界幂生成的离散多拟阵的凸包，给出了形如 conv(D(G,c)) 的 Gorenstein 多面体的分类。
Multiplicity Bounds for Quadratic Monomial Ideals
本文证明了Herzog-Huneke-Srinivasan和Herzog-Srinivasan关于二部图的边理想的强猜想和关于二次单项理想的弱Taylor界猜想。我们附加一个有向图的二部图与完美匹配，并描述操作的有向图，将减少问题的科恩-麦考利二部图。我们确定了在二部图的边理想的限制界中等式成立的条件，并证明了当等式成立时，分解是纯的。刻画了具有Cohen-Macaulay边理想和拟纯分解的二部图.
Given an arbitrary field k and an arithmetic sequence of positive integers m_0<...<m_n, we consider the affine monomial curve parameterized by X_0=t^{m_0},...,X_n=t^{m_n}. In this paper, we conjecture that the Betti numbers of its coordinate ring are completely determined by n and the value of m_0 modulo n. We first show that the defining ideal of the monomial curve can be written as a sum of two determinantal ideals. Using this fact, we describe the minimal free resolution of the coordinate ring in the following three cases: when m_0 is 1 modulo n (determinantal), when m_0 is n modulo n (almo…
Duality, a-invariants and canonical modules of rings arising from linear optimization problems
本文的目的是研究各种线性不等式组的整数舍入性质，以深入了解单项式理想和单项式子环的Rees代数的代数性质。本文研究了具有整数舍入性质的Rees代数和子环的正规性和Gorenstein性质，以及正则模和a-不变量。本文将Rees代数和单项子环的代数性质与整数舍入性质联系起来，给出了一个对偶定理。
The toric ring of one dimensional simplicial complexes
本文研究一维单纯复形（即有限简单图）的环面环，分类正规情形并刻画其 Gorenstein 与伪 Gorenstein 性质。
Determining whether an arbitrary subring $R$ of $k[x_1^{\pm 1},\dots, x_n^{\pm 1}]$ is a normal domain is, in general, a nontrivial problem, even in the special case of a monomial generated domain. In this paper, we provide a complete characterization of the normality and normalizations of quadratic-monomial generated domains. For a quadratic-monomial generated domain $R$, we develop a combinatorial structure that assigns, to each quadratic monomial of the ring, an edge in a mixed signed, directed graph $G$, i.e., a graph with signed edges and directed edges. We classify the normality and the …
We use combinatorics tools to reobtain the classification of monomial quadratic Cremona transformations in any number of variables given in \cite{SV2} and to classify and count square free cubic Cremona maps with at most six variables, up to isomorphism.
Monomial projections of Veronese varieties: new results and conjectures
本文研究Veronese簇单项式投影的齐次坐标环，证明了特定变量支撑条件下的二次代数性质，并完全刻画了二维情形下群不变量环的二次性与Koszul等价性。
We consider the directed union S of an infinite sequence {(R_n, m_n)} of successive local quadratic transforms of a regular local ring (R, m). If dim R = 2, Abhyankar proves that S is a valuation ring. If dim R > 2, Shannon gives necessary and sufficient conditions for S to be a rank 1 valuation domain and Granja gives necessary and sufficient conditions that S be a rank 2 rational rank 2 valuation domain. Granja observes that these are the only cases where S is a valuation domain. If the sequence is along a rank 1 valuation ring V with valuation v, Granja, Martinez, and Rodriguez show that if…
We introduce a new way to associate a simplicial complex called the \emph{survival complex} to a commutative semigroup with zero. Restricting our attention to the semigroup of monomials arising from an Artinian monomial ring, we determine that any such complex has an isolated point. Indeed, we show that there is exactly one isolated point essentially only in the case where the monomial ideal is generated purely by powers of the variables. This allows us to recover Beintema's result that an Artinian monomial ring is Gorenstein if and only if it is a complete intersection. A key ingredient of th…
The strong Lefschetz property for quadratic reverse lexicographic ideals
本文研究含平方变量与反字典序无平方二次项的理想，刻画其 Hilbert 级数，并证明其商代数在特征零及充分高正特征下具有强 Lefschetz 性质。
Let I be a finitely supported complete m-primary ideal of a regular local ring (R, m). A theorem of Lipman implies that I has a unique factorization as a *-product of special *-simple complete ideals with possibly negative exponents for some of the factors. The existence of negative exponents occurs if the dimension of R is at least 3 because of the existence of finitely supported *-simple ideals that are not special. We consider properties of special *-simple complete ideals such as their Rees valuations and point basis. Let (R, m) be a d-dimensional equicharacterstic regular local ring with …
The order polytope $\mathcal{O}(P)$ and the chain polytope $\mathcal{C}(P)$ associated to a partially ordered set $P$ are studied. In this paper, we introduce the convex polytope $Γ(\mathcal{O}(P), -\mathcal{C}(Q))$ which is the convex hull of $\mathcal{O}(P) \cup (-\mathcal{C}(Q))$, where both $P$ and $Q$ are partially ordered sets with $|P|=|Q|=d$. It will be shown that $Γ(\mathcal{O}(P), -\mathcal{C}(Q))$ is a normal and Gorenstein Fano polytope by using the theory of reverse lexicographic squarefree initial ideals of toric ideals.
A graph-theoretic method, simpler than existing ones, is used to characterize the minimal set of monomial generators for the integral closure of any algebra of polynomials generated by quadratic monomials. The toric ideal of relations between these generators is generated by a set of binomials, defined graphically. The spectra of the original algebra and of its integral closure turn out to be canonically homeomorphic.
We investigate Rees algebras and special fiber rings obtained by blowing up specialized Ferrers ideals. This class of monomial ideals includes strongly stable monomial ideals generated in degree two and edge ideals of prominent classes of graphs. We identify the equations of these blow-up algebras. They generate determinantal ideals associated to subregions of a generic symmetric matrix, which may have holes. Exhibiting Gröbner bases for these ideals and using methods from Gorenstein liaison theory, we show that these determinantal rings are normal Cohen-Macaulay domains that are Koszul, that …
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