Index to other pages on regular maps;
indexes to those on
S0
C1
S1
S2
S3
S4.
Some Cayley diagrams drawn on the torus.
Some pages on groups
Copyright N.S.Wedd 2009
This page links to three pages (links above) showing some of the regular maps that can be drawn on the genus-1 orientable manifold, the torus. All those with 50 or fewer faces, and their duals, are shown. For the purpose of these pages, a "regular map" is defined here.
For other oriented manifolds, the number of such figures is small, but for the torus, it is infinite. A reason why there are so many for the torus, and a finite number for every other oriented 2-manifold, is that the torus has an Euler characteristic of 0. Thus, once we have found one regular map, we can stitch together several copies of it, to form another which still fits on a torus.
As the "curvature" of the torus is 0, its vertices must be "flat": if they are also fully symmetrical, they must be formed from four squares, or three hexagons, or six triangles. Infinitely many regular maps of each of these three types exist.
There is one regular map with four squares meeting at each vertex for each pair of non-negative integers a,b (except for 0,0). Each has a number of faces equal to a2+b2. Regular maps for integer pairs a,b with a<b exist, but are not shown here; they are the enantiomorphs of those for b,a.
All these regular maps are all self-dual.
The notation {4,4}(a,b) is consistent with that used in ARM, page 18.
ARM disallows (in our notation) {4,4}(1,0), in which the single square shares two edges with itself; and {4,4}(1,1), in which each of the two squares shares each of its vertices (but no edge) with itself.
Any {4,4} can be cantellated, yielding a {4,4} with twice as many vertices, faces and edges.
The regular maps with three hexagons meeting at each vertex are more complicated. They can all be generated from pairs of number of the form a,b where a and b are either both odd or both even. The number of faces of these regular maps is given by (a2+3*b2)/4.
More than one such pair can generate the same regular regular map, for example {6,3}(2,4), {6,3}(5,3), and {6,3}(7,1) are all the same regular map, with 13 faces. I have arbitrarily chosen to list them in ascending order of the first parameter, which is necessarily also descending order of the second parameter.
Most of these regular map are chiral, and so occur as enantiomorphic pairs. Only one (arbitrarily chosen) member of each such pair is shown.
The notation {6,3}(a,b) used here is not consistent with that used in ARM, page 19. Where ARM writes {6,3}(s,0) we write {6,3}(s,s), and where ARM writes {6,3}(s,s) we write {6,3}(0, 2s).
ARM disallows regular maps which (in our notation) are not of either of the forms {6,3}(s,s) and {6,3}(0, 2s), because they lack "full reflexional symmetry", i.e. they are chiral. It also disallows (in our notation) {6,3}(1,1), in which the single hexagon shares three edges with itself.
The regular maps with six triangles meeting at each vertex are the duals of those with three hexagons. As for {6,3}(a,b), a and b must be either both odd or both even. The number of faces of these polyhedra is given by (a2+3*b2)/2.
The notation used here {3,6}(a,b) is not consistent with that used in ARM, and is as described above for {6,3}(a,b). Thus our {6,3}(a,b) is the dual of our {3,6}(a,b).
ARM also disallows (in our notation) {3,6}(1,1), in which each of the two triangles shares each of its vertices (but no edge) with itself.
Index to other pages on regular maps;
indexes to those on
S0
C1
S1
S2
S3
S4.
Some Cayley diagrams drawn on the torus.
Some pages on groups
Copyright N.S.Wedd 2009