An integer sequence and standard monomials

2018 ◽  
Vol 17 (02) ◽  
pp. 1850037
Author(s):  
Ajay Kumar ◽  
Chanchal Kumar
Keyword(s):  
Spanning Trees ◽  
Monomial Ideal ◽  
Oriented Graph ◽  
Barycentric Subdivision ◽  
Parking Functions ◽  
Minimal Free Resolution ◽  
Ideal Formula ◽  
Laplace Matrix ◽  
Integer Sequence ◽  
Standard Monomials

For an (oriented) graph [Formula: see text] on the vertex set [Formula: see text] (rooted at [Formula: see text]), Postnikov and Shapiro (Trans. Amer. Math. Soc. 356 (2004) 3109–3142) associated a monomial ideal [Formula: see text] in the polynomial ring [Formula: see text] over a field [Formula: see text] such that the number of standard monomials of [Formula: see text] equals the number of (oriented) spanning trees of [Formula: see text] and hence, [Formula: see text], where [Formula: see text] is the truncated Laplace matrix of [Formula: see text]. The standard monomials of [Formula: see text] correspond bijectively to the [Formula: see text]-parking functions. In this paper, we study a monomial ideal [Formula: see text] in [Formula: see text] having rich combinatorial properties. We show that the minimal free resolution of the monomial ideal [Formula: see text] is the cellular resolution supported on a subcomplex of the first barycentric subdivision [Formula: see text] of an [Formula: see text] simplex [Formula: see text]. The integer sequence [Formula: see text] has many interesting properties. In particular, we obtain a formula, [Formula: see text], with [Formula: see text] for [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text], similar to [Formula: see text].

scholarly journals Skeleton Ideals of Certain Graphs, Standard Monomials and Spherical Parking Functions

10.37236/9874 ◽  
2021 ◽  
Vol 28 (1) ◽  
Author(s):  
Chanchal Kumar ◽  
Gargi Lather ◽  
Sonica
Keyword(s):  
Monomial Ideal ◽  
Betti Numbers ◽  
Additional Parameter ◽  
Parking Functions ◽  
Combinatorial Interpretation ◽  
Parking Function ◽  
Combinatorial Properties ◽  
Standard Monomials ◽  
Chip Firing ◽  
Vertex Set

 Let $G$ be a graph on the vertex set $V = \{ 0, 1,\ldots,n\}$ with root $0$. Postnikov and Shapiro were the first to consider a monomial ideal $\mathcal{M}_G$, called the $G$-parking function ideal, in the polynomial ring $ R = {\mathbb{K}}[x_1,\ldots,x_n]$ over a field $\mathbb{K}$ and explained its connection to the chip-firing game on graphs. The standard monomials of the Artinian quotient $\frac{R}{\mathcal{M}_G}$ correspond bijectively to $G$-parking functions. Dochtermann introduced and studied skeleton ideals of the graph $G$, which are subideals of the $G$-parking function ideal with an additional parameter $k ~(0\le k \le n-1)$. A $k$-skeleton ideal $\mathcal{M}_G^{(k)}$ of the graph $G$ is generated by monomials corresponding to non-empty subsets of the set of non-root vertices $[n]$ of size at most $k+1$. Dochtermann obtained many interesting homological and combinatorial properties of these skeleton ideals. In this paper, we study the $k$-skeleton ideals of graphs and for certain classes of graphs provide explicit formulas and combinatorial interpretation of standard monomials and the Betti numbers.

scholarly journals Linear syzygies of Stanley-Reisner ideals

2001 ◽  
Vol 89 (1) ◽  
pp. 117 ◽  
Author(s):  
V Reiner ◽  
V Welker
Keyword(s):  
Simplicial Complex ◽  
Lower Bounds ◽  
Monomial Ideal ◽  
Independent Sets ◽  
Free Resolution ◽  
Monomial Ideals ◽  
Minimal Free Resolution ◽  
Linear Syzygies ◽  
Alexander Dual ◽  
Syzygy Modules

We give an elementary description of the maps in the linear strand of the minimal free resolution of a square-free monomial ideal, that is, the Stanley-Reisner ideal associated to a simplicial complex $\Delta$. The description is in terms of the homology of the canonical Alexander dual complex $\Delta^*$. As applications we are able to prove for monomial ideals and $j=1$ a conjecture of J. Herzog giving lower bounds on the number of $i$-syzygies in the linear strand of $j^{th}$-syzygy modules show that the maps in the linear strand can be written using only $\pm 1$ coefficients if $\Delta^*$ is a pseudomanifold exhibit an example where multigraded maps in the linear strand cannot be written using only $\pm 1$ coefficients compute the entire resolution explicitly when $\Delta^*$ is the complex of independent sets of a matroid

scholarly journals The number of generators of the powers of an ideal

2019 ◽  
Vol 29 (05) ◽  
pp. 827-847 ◽  
Author(s):  
Jürgen Herzog ◽  
Maryam Mohammadi Saem ◽  
Naser Zamani
Keyword(s):  
Lower Bounds ◽  
Principal Ideal ◽  
Monomial Ideal ◽  
Ideal Formula ◽  
Number Of Generators ◽  
Regular Rings

We study the number of generators of ideals in regular rings and ask the question whether [Formula: see text] if [Formula: see text] is not a principal ideal, where [Formula: see text] denotes the number of generators of an ideal [Formula: see text]. We provide lower bounds for the number of generators for the powers of an ideal and also show that the CM-type of [Formula: see text] is [Formula: see text] if [Formula: see text] is a monomial ideal of height [Formula: see text] in [Formula: see text] and [Formula: see text].

On the reduction numbers of monomial ideals

2019 ◽  
Vol 19 (10) ◽  
pp. 2050201
Author(s):  
Ibrahim Al-Ayyoub
Keyword(s):  
Polynomial Ring ◽  
Monomial Ideal ◽  
Upper Bounds ◽  
Integral Closure ◽  
Monomial Ideals ◽  
Explicit Method ◽  
Generating Set ◽  
Ideal Formula ◽  
Reduction Number ◽  
The Ideal

Let [Formula: see text] be a monomial ideal in a polynomial ring with two indeterminates over a field. Assume [Formula: see text] is contained in the integral closure of some ideal that is generated by two elements from the generating set of [Formula: see text]. We produce sharp upper bounds for each of the reduction number and the Ratliff–Rush reduction number of the ideal [Formula: see text]. Under certain hypotheses, we give the exact values of these reduction numbers, and we provide an explicit method for obtaining these sharp upper bounds.

A study of a family of monomial ideals

2021 ◽  
Author(s):  
J. William Hoffman ◽  
Haohao Wang
Keyword(s):  
Structural Properties ◽  
Monomial Ideal ◽  
Free Resolution ◽  
Monomial Ideals ◽  
Symmetric Algebra ◽  
Rees Algebra ◽  
Implicit Equation ◽  
Ideal Formula ◽  
Moving Planes

In this paper, we study a family of rational monomial parametrizations. We investigate a few structural properties related to the corresponding monomial ideal [Formula: see text] generated by the parametrization. We first find the implicit equation of the closure of the image of the parametrization. Then we provide a minimal graded free resolution of the monomial ideal [Formula: see text], and describe the minimal graded free resolution of the symmetric algebra of [Formula: see text]. Finally, we provide a method to compute the defining equations of the Rees algebra of [Formula: see text] using three moving planes that follow the parametrization.

scholarly journals On the number of spanning trees, the Laplacian eigenvalues, and the Laplacian Estrada index of subdivided-line graphs

2016 ◽  
Vol 14 (1) ◽  
pp. 641-648 ◽  
Author(s):  
Yilun Shang
Keyword(s):  
Spanning Trees ◽  
Line Graph ◽  
Upper And Lower Bounds ◽  
Barycentric Subdivision ◽  
Electrical Networks ◽  
Zagreb Index ◽  
Laplacian Eigenvalues ◽  
Estrada Index ◽  
Vertex Degrees ◽  
Number Of Spanning Trees

Abstract As a generalization of the Sierpiński-like graphs, the subdivided-line graph Г(G) of a simple connected graph G is defined to be the line graph of the barycentric subdivision of G. In this paper we obtain a closed-form formula for the enumeration of spanning trees in Г(G), employing the theory of electrical networks. We present bounds for the largest and second smallest Laplacian eigenvalues of Г(G) in terms of the maximum degree, the number of edges, and the first Zagreb index of G. In addition, we establish upper and lower bounds for the Laplacian Estrada index of Г(G) based on the vertex degrees of G. These bounds are also connected with the number of spanning trees in Г(G).

scholarly journals Spanning forests, electrical networks, and a determinant identity

2009 ◽  
Vol DMTCS Proceedings vol. AK,... (Proceedings) ◽  
Author(s):  
Elmar Teufl ◽  
Stephan Wagner
Keyword(s):  
Spanning Trees ◽  
Symmetric Graph ◽  
Electrical Networks ◽  
Laplace Matrix ◽  
Nous Montrons ◽  
Spanning Forests ◽  
International Audience ◽  
Self Similar ◽  
Algebraic Proofs

International audience We aim to generalize a theorem on the number of rooted spanning forests of a highly symmetric graph to the case of asymmetric graphs. We show that this can be achieved by means of an identity between the minor determinants of a Laplace matrix, for which we provide two different (combinatorial as well as algebraic) proofs in the simplest case. Furthermore, we discuss the connections to electrical networks and the enumeration of spanning trees in sequences of self-similar graphs. Nous visons à généraliser un théorème sur le nombre de forêts couvrantes d'un graphe fortement symétrique au cas des graphes asymétriques. Nous montrons que cela peut être obtenu au moyen d'une identité sur les déterminants mineurs d'une matrice Laplacienne, pour laquelle nous donnons deux preuves différentes (combinatoire ou bien algébrique) dans le cas le plus simple. De plus, nous discutons les relations avec des réseaux électriques et l'énumération d'arbres couvrants dans de suites de graphes autosimilaires.

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