P_nodal and Psi_nodal are no longer diluted toward zero on the domain boundary: pressure's and the particle scalar's dummy cells now repeat the adjacent cell (zero normal gradient), filled by UpdateDummyCells, which now takes the field it fills. Analytical flows now synchronize periodic dummy cells as the solved flow does, which corrects periodic UNIFORM_FLOW and TGV3D velocity dummies. Page 57 records what a pressure boundary condition would involve.