code: def hexagonal(a: float, c: float):
          
          return Lattice.from_parameters(a, a, c, 90, 90, 120)
docs: Convenience constructor for a hexagonal lattice.
  
          Args:
              a (float): *a* lattice parameter of the hexagonal cell.
              c (float): *c* lattice parameter of the hexagonal cell.
  
          Returns:
              Hexagonal lattice of dimensions a x a x c.