9 research outputs found
Locked Polyomino Tilings
A locked -omino tiling is a grid tiling by -ominoes such that, if you
remove any pair of tiles, the only way to fill in the remaining grid cells
with -ominoes is to use the same two tiles in the exact same configuration
as before. We exclude degenerate cases where there is only one tiling overall
due to small dimensions. It is a classic (and straightforward) result that
finite grids do not admit locked 2-omino tilings. In this paper, we construct
explicit locked -omino tilings for on grids of various
dimensions. Most notably, we show that locked 3- and 4-omino tilings exist on
finite square grids of arbitrarily large size, and locked -omino tilings of
the infinite grid exist for arbitrarily large . The result for 4-omino
tilings in particular is remarkable because they are so rare and difficult to
construct: Only a single tiling is known to exist on any grid up to size .
Locked -omino tilings arise as obstructions to widely used political
redistricting algorithms in a model of redistricting where the underlying
census geography is a grid graph. Most prominent is the ReCom Markov chain,
which takes a random walk on the space of redistricting plans by iteratively
merging and splitting pairs of districts (tiles) at a time. Locked -omino
tilings are isolated states in the state space of ReCom. The constructions in
this paper are counterexamples to the meta-conjecture that ReCom is irreducible
on graphs of practical interest
Tiling a simply connected figure with bars of length 2 or 3
AbstractLet F be a simply connected figure formed from a finite set of cells of the planar square lattice. We first prove that if F has no peak (a peak is a cell of F which has three of its edges in the contour of F), then F can be tiled with rectangular bars formed from 2 or 3 cells. Afterwards, we devise a linear-time algorithm for finding a tiling of F with those bars when such a tiling exists
Tiling with Bars and Satisfaction of Boolean Formulas
AbstractLetFbe a figure formed from a finite set of cells of the planar square lattice. We first prove that the problem of tiling such a figure with bars formed from 2 or 3 cells can be reduced to the logic problem 2-SAT. Afterwards, we deduce a linear-time algorithm of tiling with these bars
Local dimer dynamics in higher dimensions
We consider local dynamics of the dimer model (perfect matchings) on
hypercubic boxes . These consist of successively switching the dimers
along alternating cycles of prescribed (small) lengths. We study the
connectivity properties of the dimer configuration space equipped with these
transitions. Answering a question of Freire, Klivans, Milet and Saldanha, we
show that in three dimensions any configuration admits an alternating cycle of
length at most 6. We further establish that any configuration on
features order alternating cycles of length at most . We also
prove that the dynamics of dimer configurations on the unit hypercube of
dimension is ergodic when switching alternating cycles of length at most
. Finally, in the planar but non-bipartite case, we show that
parallelogram-shaped boxes in the triangular lattice are ergodic for switching
alternating cycles of lengths 4 and 6 only, thus improving a result of Kenyon
and R\'emila, which also uses 8-cycles. None of our proofs make reference to
height functions.Comment: 14 pages, 4 figure
Ergodic Archimedean dimers
We study perfect matchings, or close-packed dimer coverings, of finite
sections of the eleven Archimedean lattices and give a constructive proof
showing that any two perfect matchings can be transformed into each other using
small sets of local ring-exchange moves. This result has direct consequences
for formulating quantum dimer models with a resonating valence bond ground
state, i.e., a superposition of all dimer coverings compatible with the
boundary conditions. On five of the composite Archimedean lattices we
supplement the sufficiency proof with translationally invariant reference
configurations that prove the strict necessity of the sufficient terms with
respect to ergodicity. We provide examples of and discuss frustration-free
deformations of the quantum dimer models on two tripartite lattices.Comment: Submission to SciPost; 21 pages, 17 figure
Some tiling moves explored
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1998.Includes bibliographical references (p. 135).by David Gupta.Ph.D