In geometry , the 5-CELL is a four-dimensional object bounded by 5
tetrahedral cells . It is also known as a C5, PENTACHORON, PENTATOPE,
PENTAHEDROID, or TETRAHEDRAL PYRAMID . It is a 4-SIMPLEX , the
simplest possible convex regular 4-polytope (four-dimensional analogue
of a
The REGULAR 5-CELL is bounded by regular tetrahedra , and is one of the six regular convex 4-polytopes , represented by Schläfli symbol {3,3,3}. CONTENTS * 1 Alternative names * 2.1 Construction
* 2.2
* 3 Irregular
ALTERNATIVE NAMES * Pentachoron * 4-simplex * Pentatope * Pentahedroid (Henry Parker Manning) * Pen (Jonathan Bowers: for pentachoron) * Hyperpyramid, tetrahedral pyramid GEOMETRY The
CONSTRUCTION The
The simplest set of coordinates is: (2,0,0,0), (0,2,0,0), (0,0,2,0), (0,0,0,2), (τ,τ,τ,τ), with edge length 2√2, where τ is the golden ratio . The
Another set of origin-centered coordinates in 4-space can be seen as a hyperpyramid with a regular tetrahedral base in 3-space, with edge length 2√2: ( 1 , 1 , 1 , 1 / 5 ) {displaystyle left(1,1,1,-1/{sqrt {5}}right)} ( 1 , 1 , 1 , 1 / 5 ) {displaystyle left(1,-1,-1,-1/{sqrt {5}}right)} ( 1 , 1 , 1 , 1 / 5 ) {displaystyle left(-1,1,-1,-1/{sqrt {5}}right)} ( 1 , 1 , 1 , 1 / 5 ) {displaystyle left(-1,-1,1,-1/{sqrt {5}}right)} ( 0 , 0 , 0 , 5 1 / 5 ) {displaystyle left(0,0,0,{sqrt {5}}-1/{sqrt {5}}right)} The vertices of a 4-simplex (with edge √2) can be more simply
constructed on a hyperplane in 5-space, as (distinct) permutations of
(0,0,0,0,1) or (0,1,1,1,1); in these positions it is a facet of,
respectively, the
BOERDIJK–COXETER HELIX A
PROJECTIONS The A4
orthographic projections
Ak
GRAPH DIHEDRAL SYMMETRY PROJECTIONS TO 3 DIMENSIONS
A 3D projection of a
The vertex-first projection of the
The face-first projection of the
IRREGULAR 5-CELL There are many lower symmetry forms, including these found in uniform polytope vertex figures : SYMMETRY Order 120 Order 24 Order 12 Order 6 + Order 10 NAME Regular 5-cell Tetrahedral pyramid Triangular-pyramidal pyramid Pentagonal hyperdisphenoid SCHLäFLI SYMBOL {3,3,3} {3,3} ∨ ( ) {3} ∨ { } Example
Vertex
figure
The TETRAHEDRAL PYRAMID is a special case of a 5-CELL, a polyhedral pyramid , constructed as a regular tetrahedron base in a 3-space hyperplane , and an apex point above the hyperplane. The four sides of the pyramid are made of tetrahedron cells. Many uniform 5-polytopes have TETRAHEDRAL PYRAMID vertex figures : Symmetry , order 24 Schlegel diagram Name Coxeter diagram { }×{3,3,3} { }×{4,3,3} { }×{5,3,3} t{3,3,3,3} t{4,3,3,3} t{3,4,3,3} Other uniform 5-polytopes have irregular
SYMMETRY , ORDER 12 , ORDER 6 , ORDER 8 , ORDER 4 Schlegel diagram Name Coxeter diagram t12α5 t12γ5 t012α5 t012γ5 t123α5 t123γ5 SYMMETRY , ORDER 2 , ORDER 2 +, ORDER 1 Schlegel diagram Name Coxeter diagram t0123α5 t0123γ5 t0123β5 t01234α5 t01234γ5 COMPOUND The compound of two 5-cells in dual configurations can be seen in
this A5
RELATED POLYTOPES AND HONEYCOMB The pentachoron (5-cell) is the simplest of 9 uniform polychora
constructed from the
SCHLäFLI {3,3,3} T{3,3,3} R{3,3,3} RR{3,3,3} 2T{3,3,3} TR{3,3,3} T0,3{3,3,3} T0,1,3{3,3,3} T0,1,2,3{3,3,3} COXETER SCHLEGEL 1K2 FIGURES IN N DIMENSIONS SPACE FINITE EUCLIDEAN HYPERBOLIC N 3 4 5 6 7 8 9 10 Coxeter group E3=A2A1 E4=A4 E5=D5 E6 E7 E8 E9 = E 8 {displaystyle {tilde {E}}_{8}} = E8+ E10 = T 8 {displaystyle {bar {T}}_{8}} = E8++ Coxeter diagram Symmetry (order) ] ORDER 12 120 192 103,680 2,903,040 696,729,600 ∞ GRAPH - - NAME 1−1,2 102 112 122 132 142 152 162 2K1 FIGURES IN N DIMENSIONS SPACE FINITE EUCLIDEAN HYPERBOLIC N 3 4 5 6 7 8 9 10 Coxeter group E3=A2A1 E4=A4 E5=D5 E6 E7 E8 E9 = E 8 {displaystyle {tilde {E}}_{8}} = E8+ E10 = T 8 {displaystyle {bar {T}}_{8}} = E8++ Coxeter diagram SYMMETRY ] ORDER 12 120 384 51,840 2,903,040 696,729,600 ∞ GRAPH - - NAME 2−1,1 201 211 221 231 241 251 261 It is in the sequence of regular polychora : the tesseract {4,3,3},
{P,3,3} POLYTOPES SPACE S3 H3 FORM FINITE PARACOMPACT NONCOMPACT NAME {3,3,3} {4,3,3} {5,3,3} {6,3,3} {7,3,3} {8,3,3} ... {∞,3,3} IMAGE Cells {p,3} {3,3} {4,3} {5,3} {6,3} {7,3} {8,3} {∞,3} It is similar to three regular polychora : the tesseract {4,3,3},
{3,3,P} POLYTOPES SPACE S3 H3 FORM FINITE PARACOMPACT NONCOMP |