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arXiv 2310.05005math.CO
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平衡极小循环复形的刚性

Rigidity of Balanced Minimal Cycle Complexes

Ryoshun Oba

AI总结:

本文将平衡正规伪流形的刚性及平衡下界定理推广到平衡极小循环复形,并研究平衡及$\bm{a}$-平衡单纯复形的无穷小刚性,证明高维平衡同调流形可实现为坐标轴上的无穷小刚体框架。

摘要:

若一个$(d-1)$维单纯复形$\Delta$的图$G(\Delta)$是可$d$着色的,则称其为平衡的。Klee和Novik针对$d\geq3$的平衡正规$(d-1)$-伪流形$\Delta$得到了平衡下界定理,证明了对任意3种颜色的集合$T$,由$T$着色的顶点诱导的$G(\Delta)$子图在$\mathbb{R}^3$中是刚性的。我们证明,对于$d\geq3$的平衡极小$(d-1)$-循环复形,同样的刚性结果成立,因此平衡下界定理也成立。受Stanley关于平衡单纯复形的Stanley-Reisner环的着色参数系工作的启发,我们进一步研究了平衡(更广泛地说是$\bm{a}$-平衡)单纯复形的非通用实现的无穷小刚性。在其他结果中,我们证明对于$d\geq4$,平衡同调$(d-1)$-流形可在$\mathbb{R}^d$中实现为无穷小刚体框架,其中颜色为$i$的每个顶点都位于第$i$条坐标轴上。

英文摘要:

A $(d-1)$-dimensional simplicial complex $Δ$ is balanced if its graph $G(Δ)$ is $d$-colorable. Klee and Novik obtained the balanced lower bound theorem for balanced normal $(d-1)$-pseudomanifolds $Δ$ with $d\geq3$ by showing that the subgraph of $G(Δ)$ induced by the vertices colored in $T$ is rigid in $\mathbb{R}^3$ for any $3$ colors $T$. We show that the same rigidity result, and thus the balanced lower bound theorem, holds for balanced minimal $(d-1)$-cycle complexes with $d \geq 3$. Motivated by the Stanley's work on a colored system of parameters for the Stanley-Reisner ring of balanced simplicial complexes, we further investigate the infinitesimal rigidity of non-generic realization of balanced, and more broadly $\bm{a}$-balanced, simplicial complexes. Among other results, we show that for $d \geq 4$, a balanced homology $(d-1)$-manifold can be realized as an infinitesimally rigid framework in $\mathbb{R}^d$ such that each vertex of color $i$ lies on the $i$th coordinate axis.

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