A cube is an example of a rectangular one of these; A Pink Floyd cover displays a triangular one
.... in an 
M-dimensional simplex (1D interval, 2D triangle, 3D tetrahedron, and... [DOC] [TLE] C Source Codes - People [PAR] Aug 10, 2016 ... ... for functions which are regular, log(x) singular, or 1/sqrt(x) singular.