Hexagonal snowflake formation via the Reiter cellular automaton
Cells frozen: 1
Reiter model (1995): each hexagonal cell is either frozen ice, boundary, or vapor.
Boundary cells freeze based on their neighbors; vapor diffuses continuously.
The parameter ρ controls background vapor density — lower ρ = more branched crystals.
Hexagonal symmetry emerges spontaneously from the lattice and diffusion rules.