Distinct Point Sets With Same Distances
A given configuration of n points in space uniquely determines
n(n-1)/2 point-to-point separations, but the converse is not true.
Given a set of n(n-1)/2 separations there may be more than one
configuration of n points with those separations. For example,
given the set of 10 separations
1, 1, 1, 1, sqrt(2), sqrt(2), 2, 2, sqrt(5), sqrt(5)
we can construct either of the two 5-point configurations shown below
b c d a b c
a e d
e
Can anyone provide other examples of such "equivalent configurations",
i.e., two or more distinct configurations of points (not counting
rotations and reflections) sharing the same set of point-to-point
separations? It's also possible to construct one-dimensional examples.
as discussed in Isospectral Sets In One Dimension.
I think the following THREE distinct configurations of eight points
each have the same set of 28 point-to-point separations:
* * * * * * * * * *
* * * *
* * * * *
* * * * *
Of the 12870 possible arrangements of eight points on a 4x4 grid, I
think there are only 1120 different sets of separations. Of course,
a lot of this reduction is due to rotations and reflections, but not
all. It appears that such configurations are not uncommon.
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