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Freeness for Restriction Arrangements of the Extended Shi and Catalan Arrangements

open access: yesDiscrete Mathematics, 2023
The extended Shi and Catalan arrangements are well investigated arrangements. In this paper, we prove that the cone of the extended Catalan arrangement of type A is always hereditarily free, while we determine the dimension in which the cone of the extended Shi arrangement of type A is hereditarily free.
Shuhei Tsujie, Norihiro Nakashima
exaly   +4 more sources

On the Falk Invariant of Shi and Linial Arrangements [PDF]

open access: yesDiscrete and Computational Geometry, 2021
It is an open question to give a combinatorial interpretation of the Falk invariant of a hyperplane arrangement, i.e. the third rank of successive quotients in the lower central series of the fundamental group of the arrangement. In this article, we give a combinatorial formula for this invariant in the case of hyperplane arrangements that are complete
Michele Torielli, Weili Guo
exaly   +5 more sources
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Free Subarrangements of Shi Arrangements

Graphs and Combinatorics, 2022
zbMATH Open Web Interface contents unavailable due to conflicting licenses.
Zixuan Wang, Guangfeng Jiang
exaly   +3 more sources

Shi Threshold Arrangement [PDF]

open access: yesElectronic Journal of Combinatorics, 2012
Richard Stanley suggested the problem of finding the number of regions and the characteristic polynomial of a certain hyperplane arrangement defined by $x_i + x_j=0,1$, which is called the Shi threshold arrangement. We present the answer of the problem, using the finite field method.
Seunghyun Seo
exaly   +4 more sources

Ad-Nilpotent Ideals and the Shi Arrangement

open access: yesJournal of Combinatorial Theory - Series A, 2013
We extend the Shi bijection from the Borel subalgebra case to parabolic subalgebras. In the process, the $I$-deleted Shi arrangement $\texttt{Shi}(I)$ naturally emerges. This arrangement interpolates between the Coxeter arrangement $\texttt{Cox}$ and the Shi arrangement $\texttt{Shi}$, and breaks the symmetry of $\texttt{Shi}$ in a certain symmetrical ...
Chao-Ping Dong
exaly   +3 more sources

A Simple Bijection for the Regions of the Shi Arrangement of Hyperplanes

open access: yesDiscrete Mathematics, 1999
The Shi arrangement ${\mathcal S}_n$ is the arrangement of affine hyperplanes in ${\mathbb R}^n$ of the form $x_i - x_j = 0$ or $1$, for $1 \leq i < j \leq n$. It dissects ${\mathbb R}^n$ into $(n+1)^{n-1}$ regions, as was first proved by Shi. We give a simple bijective proof of this result. Our bijection generalizes easily to any subarrangement of $
Christos A. Athanasiadis
exaly   +4 more sources

Hyperplane Arrangements Between Shi and Ish [PDF]

open access: yesElectronic Notes in Discrete Mathematics, 2018
Abstract We introduce a new family of hyperplane arrangements in dimension n ≥ 3 that includes both the Shi arrangement and the Ish arrangement. We prove that all the members of this family have the same number of regions — the connected components of the complement of the union of the hyperplanes — which can be bijectively labeled with the ...
Rui Duarte, Antonio Guedes de Oliveira
exaly   +4 more sources

Lattice Point Counts for the Shi Arrangement and Other Affinographic Hyperplane Arrangements

open access: yesJournal of Combinatorial Theory - Series A, 2007
13 ...
Thomas Zaslavsky, David Forge
exaly   +3 more sources

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