def fractional_from_cartesian(coordinate, lattice_array):
    """Return a fractional coordinate from a cartesian one."""
    deorthogonalisation_M = np.matrix(np.linalg.inv(lattice_array))
    fractional = deorthogonalisation_M * coordinate.reshape(-1, 1)
    return np.array(fractional.reshape(1, -1))
Return a fractional coordinate from a cartesian one.