论文标题

Toroidal Maxwell-Cremona-Delaunay通信

A Toroidal Maxwell-Cremona-Delaunay Correspondence

论文作者

Erickson, Jeff, Lin, Patrick

论文摘要

我们考虑三类图形在欧几里得平坦Tori上的地理嵌入:(1)嵌入$γ$的环形图是正平衡的,如果可以将正重放在边缘上,以便将加权边缘矢量入射到每个顶点$γ$ sum of $γ$ sum to Zero。 (2)如果嵌入$γ$的环形图是互惠的,如果将其双重的$γ^*$嵌入$γ$的每个边缘与$γ^*$的相应双边缘正交。 (3)如果可以将权重分配给顶点,则嵌入$γ$的环形图是连贯的,因此$γ$是其顶点的(固有的)加权Delaunay图。经典的Maxwell-Cremona对应关系以及凸壳之间的众所周知的对应关系和加权的Delaunay三角剖分意味着平面图嵌入(带有凸出外部面)的类似概念是等效的。实际上,这三个条件均等效于$γ$,是$ \ mathbb {r}^3 $的下凸壳的1 skeleton的投影。但是,这种三向等效性并未直接延伸至扁平托里(Flat Tori)上的地球图嵌入。在任何平坦的圆环上,相互和连贯的嵌入都是等效的,每个互相嵌入都处于正平衡状态,但并非每个正平衡嵌入均为互惠。我们建立了较弱的对应关系:任何扁平圆环上的每个正平衡都与互相/相干嵌入在某些平坦的圆环上相当。

We consider three classes of geodesic embeddings of graphs on Euclidean flat tori: (1) A toroidal graph embedding $Γ$ is positive equilibrium if it is possible to place positive weights on the edges, such that the weighted edge vectors incident to each vertex of $Γ$ sum to zero. (2) A toroidal graph embedding $Γ$ is reciprocal if there is a geodesic embedding $Γ^*$ of its dual on the same flat torus, where each edge of $Γ$ is orthogonal to the corresponding dual edge in $Γ^*$. (3) A toroidal graph embedding $Γ$ is coherent if it is possible to assign weights to the vertices, so that $Γ$ is the (intrinsic) weighted Delaunay graph of its vertices. The classical Maxwell-Cremona correspondence and the well-known correspondence between convex hulls and weighted Delaunay triangulations imply that the analogous concepts for planar graph embeddings (with convex outer faces) are equivalent. Indeed, all three conditions are equivalent to $Γ$ being the projection of the 1-skeleton of the lower convex hull of points in $\mathbb{R}^3$. However, this three-way equivalence does not extend directly to geodesic graph embeddings on flat tori. On any flat torus, reciprocal and coherent embeddings are equivalent, and every reciprocal embedding is in positive equilibrium, but not every positive equilibrium embedding is reciprocal. We establish a weaker correspondence: Every positive equilibrium embedding on any flat torus is affinely equivalent to a reciprocal/coherent embedding on some flat torus.

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