|hull [hʌl]||（这个不是几何术语）outer covering (of a fruit, seed, ship or tank etc.)|
|face||面，不过在 Simplex 这里与我们常用的面的概念有点不同|
In geometry, a simplex (plural simplexes or simplices) is a generalization of the notion of a triangle or tetrahedron to arbitrary dimensions. Specifically, a k-simplex is a k-dimensional polytope which is the convex hull of its k+1 vertices.
- a single point may be considered a 0-simplex
- a line segment may be considered a 1-simplex
- a triangle may be considered a 2-simplex
- a tetrahedron may be considered a 3-simplex
The convex hull of any nonempty subset of the n+1 points that define an n-simplex is called a face of the simplex. If the size of this subset is m+1, we call this face an m-face.
- 0-faces are called the vertices
- 1-faces are called the edges
- (n−1)-faces are called the facets
- the sole n-face is the whole n-simplex itself