Index of a groupsubgroup pair

The program INDEX calculates the index of a group subgroup pair. The index can be calculated in two different ways:
 Option A
 The space group ITA numbers.
 The number of atoms per conventional unit cells.
The number of atoms per conventional unit cell^{*} N_{c} is simply related to the number N of atoms per primitive unit cell via the socalled centring factor f, N=N_{c}/f, with f=1 for primitive lattices, 2 for I, C, B, A centred, 3 for Rcentred and 4 for Fcentred lattice.
 Option B
 The space group ITA numbers.
 The lattice parameters.
In some cases, due to the lattice deformation, the data on the lattice parameters (option B) might not be sufficient for the calculation of the index.
^{*}For us, the conventional cell for rhombohedral groups is the centred cell (hexagonal axes).


