The goal of this paper is to provide homological descriptions of monomial ideals. The key concepts in these descriptions are the minimal free resolution, the Koszul homology and the multigraded Betti numbers. These three objects are strongly related, being Tor modules a simple way to describe this relation. We introduce a new tool, Mayer-Vietoris trees which provides a good way to compute the h...

Let S = K[x1, . . . , xn] be a polynomial ring and R = S/I be a graded K-algebra where I ⊂ S is a graded ideal. Herzog, Huneke and Srinivasan have conjectured that the multiplicity of R is bounded above by a function of the maximal shifts in the minimal graded free resolution of R over S. We prove the conjecture in the case that codim(R) = 2 which generalizes results in [10] and [13]. We also g...

Let R be a (nonzero commutative unital) ring. If I and J are ideals of R such that R/I ⊕R/J is a cyclic R-module, then I + J = R. The rings R such that R/I ⊕R/J is a cyclic R-module for all distinct nonzero proper ideals I and J of R are the following three types of principal ideal rings: fields, rings isomorphic to K ×L for the fields K and L, and special principal ideal rings (R,M) such thatM...

Let k be a field of positive characteristic, R an associative algebra over k and let ∆1,n = {δ1, . . . , δn} be a finite set of k-linear derivations from R to R. Let A = Rn = R[θ1, δ1] · · · [θn, δn] be an iterated differential operator k-algebra over R such that δj(θi) ∈ Ri−1θi +Ri−1; 1 ≤ i < j ≤ n. As central result we show that if R is noetherian affine ∆1,n-hypernormal and if Tauvel’s heigh...

On the basis of the concept of interval valued intuitionistic fuzzy set introduced by K. Atanassov [3], the notion of interval valued intuitionistic fuzzy subsemigroup (ideal, bi-ideal, (1, 2)-ideal) of a semigroup with respect to t-norm T and s-norm S is given and the characteristic properties are described. The homomorphic image and inverse image are investigated. In particular, by the help o...

Let R be a commutative ring and Max (R) be the set of maximal ideals of R. The regular digraph of ideals of R, denoted by −−→ Γreg(R), is a digraph whose vertex set is the set of all non-trivial ideals of R and for every two distinct vertices I and J , there is an arc from I to J whenever I contains a J-regular element. The undirected regular (simple) graph of ideals of R, denoted by Γreg(R), h...

Interval variables can be measured on very different scales. We first remind a general methodology used for measuring the dispersion of a variable from an optimal center and we define two measures of dispersions associated to two optimal ”centers” for interval variables. Then we study the relations between the standardization of a data table and the use in clustering of a normalized distance. F...

We consider the Hypergraph Multiway Partition problem (Hyper-MP). The input consists of an edge-weighted hypergraph G = (V, E) and k vertices s1, . . . , sk called terminals. A multiway partition of the hypergraph is a partition (or labeling) of the vertices of G into k sets A1, . . . , Ak such that si ∈ Ai for each i ∈ [k]. The cost of a multiway partition (A1, . . . , Ak) is ∑k i=1 w(δ(Ai)), ...

This article investigates the codimension of commutator spaces [I, B(H)] of operator ideals on a separable Hilbert space, i.e., “How many traces can an ideal support?” We conjecture that the codimension can be only zero, one, or infinity. Using the arithmetic mean (am) operations on ideals introduced in [13] and the analogous arithmetic mean operations at infinity (am-∞) that we develop extensi...