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Let $G$ be a connected finite simple graph and let $I_G$ be the edge ideal of $G$. The smallest number $k$ for which $depth S/I_G^k$ stabilizes is denoted by $dstab(I_G)$. We show that $dstab(I_G)<ell(I_G)$ where $ell(I_G)$ denotes the analytic spread of $I$. For trees we give a stronger upper bound for $dstab(I_G)$. We also show for any two integers $1leq a<b$ there exists a tree for which $dstab(I_G)=a$ and $ell(I_G)=b$.
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Let $G$ be a simple graph on the vertex set $[n]$ and $J_G$ be the corresponding binomial edge ideal. Let $G=v*H$ be the cone of $v$ on $H$. In this article, we compute all the Betti numbers of $J_G$ in terms of Betti number of $J_H$ and as a consequence, we get the Betti diagram of wheel graph. Also, we study Cohen-Macaulay defect of $S/J_G$ in terms of Cohen-Macaulay defect of $S_H/J_H$ and using this we construct a graph with Cohen-Macaulay defect $q$ for any $qgeq 1$. We obtain the depth of binomial edge ideal of join of graphs. Also, we prove that for any pair $(r,b)$ of positive integers with $1leq b< r$, there exists a connected graph $G$ such that $reg(S/J_G)=r$ and the number of extremal Betti number of $S/J_G$ is $b$.
We give upper bounds for the Stanley depth of edge ideals of certain k-partite clutters. In particular, we generalize a result of Ishaq about the Stanley depth of the edge ideal of a complete bipartite graph. A result of Pournaki, Seyed Fakhari and Yassemi implies that the Stanleys conjecture holds for d-uniform complete d-partite clutters. Here we give a shorter and different proof of this fact.
We compute the Betti numbers for all the powers of initial and final lexsegment edge ideals. For the powers of the edge ideal of an anti-$d-$path, we prove that they have linear quotients and we characterize the normally torsion-free ideals. We determine a class of non-squarefree ideals, arising from some particular graphs, which are normally torsion-free.
We determine the Castelnuovo-Mumford regularity of binomial edge ideals of complement reducible graphs (cographs). For cographs with $n$ vertices the maximum regularity grows as $2n/3$. We also bound the regularity by graph theoretic invariants and construct a family of counterexamples to a conjecture of Hibi and Matsuda.
Let $mathcal{D}$ be a weighted oriented graph and let $I(mathcal{D})$ be its edge ideal. Under a natural condition that the underlying (undirected) graph of $mathcal{D}$ contains a perfect matching consisting of leaves, we provide several equivalent conditions for the Cohen-Macaulayness of $I(mathcal{D})$. We also completely characterize the Cohen-Macaulayness of $I(mathcal{D})$ when the underlying graph of $mathcal{D}$ is a bipartite graph. When $I(mathcal{D})$ fails to be Cohen-Macaulay, we give an instance where $I(mathcal{D})$ is shown to be sequentially Cohen-Macaulay.
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