The lattice mathbbZn has an essentially unique (up to permutation) minimal periodic coloring for all n, namely the "checkerboard" 2-coloring. Here a coloring of a lattice L is a coloring of the graph G=(V,E) with V=L and (x,y)inE if x and y differ by a reduced basis element. (NB. I am not quite sure that this graph is the proper one to consider in general, so comments on this would also be nice.)
The root lattice An has many minimal periodic colorings if n+1 is not prime (I have sketched this here, and some motivation is in the last post in that series); if n+1 is prime, then it has essentially one n+1-coloring. Two minimal periodic colorings for A3 are shown below (for convenience, compare the tops of the figures):
The generic ("cyclic") coloring.
A nontrivial example.
The lattices Dn are also trivially 2-colored.
So: are there other lattices that admit more than one minimal periodic coloring? I'd be especially interested to know if E8 or the Leech lattice do.
(A related question: does every minimal periodic coloring of An arise from a group of order n+1?)
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