Dan's FOM is monotone increasing, at least on Ed Pegg's original data below. -------------- Quoting Dan Asimov <dasimov@earthlink.net>:
This is really a great question!
I wonder what tends to happen for *large numbers of points*, which I suspect tend to fall into patterns except at the edges.
One surface pattern having lots of unit distances is a generalized icosahedral vertex arrangement: It has the *rotational* symmetry of an icosahedron, but instead of a single triangular face worth of just 3 vertices, each face corresponds to a triangular number of vertices:
n + (n-1) + ... + 3 + 2 + 1
in a triangular array (with faces sharing vertices at their edges.
These so far also have the same subgroup of O(3) as their full symmetry group.
But also, one can *rotate* each face the same amount (for certain angles). These arrangements can be projected radially onto a sphere to simplify visualization of them, and always have like the icosahedron exactly 12 vertices of valence = 5, with all the rest of valence = 6.
Which are dual to the atom arrangements of buckyballs and its relatives having those symmetries.
I am alas too much in a rush to calculate the
a) number N of points
and
b) number of unit distances,
but there are plenty of the latter for the former. (Maybe a simple figure of merit could be the ratio
# of unit distances fom = ??????????????????? # of points .)
It might be an interesting (therefore OEIS-worthy?) to find the numbers N of points for which fom is a local max.
?Dan
On Jun 20, 2016, at 7:52 AM, Ed Pegg Jr <ed@mathpuzzle.com> wrote:
In 3D space, with n distinct points, what is the maximal number of unit distance lengths?
I'm trying to build up a sequence for OEIS, but I'm only positive I've got the right values on two or three of the entries. Here's what I have so far.
V -- E -- figure 4 -- 6 -- tetrahedron 5 -- 9 -- triangular bipyramid 6 -- 12 -- octahedron 7 -- 15 -- pentagonal bipyramid 8 -- 18 -- snub disphenoid or Raiskii spindle 9 -- 21 -- triaugmented triangular prism 10 -- 25 -- Nechustan spindle 11 -- 28 -- Augmented Nechustan spindle 12 -- 31 -- Double Pacman spindle 13 -- 36 -- Cuboctahedron + center 14 -- 40 -- Cuboctahedron + center + pyramid 15 -- 45 -- Icosahedron + 3 internal points 16 -- 50 -- Icosahedron + 4 internal points
http://math.stackexchange.com/questions/1830194/maximal-unit-lengths-in-3d-w... has a bit more info.
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