Cell reduction and lattice symmetry determination

Simple inspection of the reduced form of a unit cell can fail to detect the correct lattice symmetry, because of the effects of measurement errors, computer rounding errors and uncertainties in interpretation of almost equal numbers. A procedure which is insensitive to these effects consists of the generation of a list of lattice vectors sorted on length, together with angles between pairs of them. The list includes the edges, face diagonals and body diagonals of the reduced cell, and the sums and differences of any of these which are similar in length. The correct unit cell is easily recognized in the vector list.