arXiv subjects

Anargyros Katsabekis

Publications and source records attributed to Anargyros Katsabekis.

21 records · Page 2Linked to original sources

arXiv2006

Minimal systems of binomial generators and the indispensable complex of a toric ideal

Let $A=\{{\bf a}_1,...,{\bf a}_m\} \subset \mathbb{Z}^n$ be a vector configuration and $I_A \subset K[x_1,...,x_m]$ its corresponding toric ideal. The paper consists of two parts. In the first part we completely determine the number of different minimal systems of binomial generators of $I_A$. We also prove that generic toric ideals are generated by indispensable binomials. In the second part we associate to $A$ a simplicial complex $Δ_{\ind(A)}$. We show that the vertices of $Δ_{\ind(A)}$ correspond to the indispensable monomials of the toric ideal $I_A$, while one dimensional facets of $Δ_{\ind(A)}$ with minimal binomial $A$-degree correspond to the indispensable binomials of $I_{A}$.

math.AC↗

arXiv2004

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.

math.AC↗

arXiv2003

Stanley-Reisner rings and the radicals of lattice ideals

In this article we associate to every lattice ideal $I_{L,ρ}\subset K[x_1,..., x_m]$ a cone $σ$ and a graph $G_σ$ with vertices the minimal generators of the Stanley-Reisner ideal of $σ$. To every polynomial $F$ we assign a subgraph $G_σ(F)$ of the graph $G_σ$. Every expression of the radical of $I_{L,ρ}$, as a radical of an ideal generated by some polynomials $F_1,..., F_s$ gives a spanning subgraph of $G_σ$, the $\cup_{i=1}^s G_σ(F_i)$. This result provides a lower bound for the minimal number of generators of $I_{L,ρ}$ and therefore improves the generalized Krull's principal ideal theorem for lattice ideals. But mainly it provides lower bounds for the binomial arithmetical rank and the $A$-homogeneous arithmetical rank of a lattice ideal. Finally we show, by a family of examples, that the bounds given are sharp.

math.AC↗