  Fermionic atoms in two different hyperfine states confined in optical
lattices show strong commensurability effects due to the interplay between the
atomic density wave (ADW) ordering and the lattice potential. We show that
spatially separated regions of commensurable and incommensurable phases can
coexist. The commensurability between the harmonic trap and the lattice sites
can be used to control the amplitude of the atomic density waves in the central
region of the trap.
