Vertex arrangementIn geometry, a vertex arrangement is a set of points in space described by their relative positions. They can be described by their use in polytopes. For example, a square vertex arrangement is understood to mean four points in a plane, equal distance and angles from a center point. Two polytopes share the same vertex arrangement if they share the same 0-skeleton. A group of polytopes that shares a vertex arrangement is called an army. The same set of vertices can be connected by edges in different ways.
Hemi-icosahedronA hemi-icosahedron is an abstract regular polyhedron, containing half the faces of a regular icosahedron. It can be realized as a projective polyhedron (a tessellation of the real projective plane by 10 triangles), which can be visualized by constructing the projective plane as a hemisphere where opposite points along the boundary are connected and dividing the hemisphere into three equal parts. It has 10 triangular faces, 15 edges, and 6 vertices.
Liste des polyèdres uniformesCette liste recense les polyèdres uniformes, ainsi que certaines de leurs propriétés. page connexe : Polyèdre régulier Un polyèdre uniforme est un polyèdre dont les faces sont des polygones réguliers et qui est isogonal (c'est-à-dire que pour tout couple de ses sommets, il existe une isométrie du polyèdre qui transforme l'un en l'autre).
Density (polytope)In geometry, the density of a star polyhedron is a generalization of the concept of winding number from two dimensions to higher dimensions, representing the number of windings of the polyhedron around the center of symmetry of the polyhedron. It can be determined by passing a ray from the center to infinity, passing only through the facets of the polytope and not through any lower dimensional features, and counting how many facets it passes through.
Truncated 120-cellsIn geometry, a truncated 120-cell is a uniform 4-polytope formed as the truncation of the regular 120-cell. There are three truncations, including a bitruncation, and a tritruncation, which creates the truncated 600-cell. The truncated 120-cell or truncated hecatonicosachoron is a uniform 4-polytope, constructed by a uniform truncation of the regular 120-cell 4-polytope. It is made of 120 truncated dodecahedral and 600 tetrahedral cells. It has 3120 faces: 2400 being triangles and 720 being decagons.
Flag (geometry)In (polyhedral) geometry, a flag is a sequence of faces of a polytope, each contained in the next, with exactly one face from each dimension. More formally, a flag ψ of an n-polytope is a set {F_–1, F_0, ..., F_n} such that F_i ≤ F_i+1 (–1 ≤ i ≤ n – 1) and there is precisely one F_i in ψ for each i, (–1 ≤ i ≤ n). Since, however, the minimal face F_–1 and the maximal face F_n must be in every flag, they are often omitted from the list of faces, as a shorthand. These latter two are called improper faces.
Ludwig SchläfliLudwig Schläfli (1814-1895) est un mathématicien suisse spécialiste en géométrie et en analyse complexe. Il a joué un rôle clé dans le développement de la notion d’espace de dimension quelconque. Ludwig Schläfli a passé la majeure partie de sa vie en Suisse. Il est né à Grasswyl, ville natale de sa mère. La famille a ensuite déménagé pour la ville proche de Berthoud, où son père était commerçant. Son père voulait que Ludwig fît le même métier que lui, mais il ne semblait pas fait pour le travail pratique.
