def center_of_coor(coordinates):
return (np.sum(coordinates, axis=<NUM_LIT:0>) / coordinates.shape[<NUM_LIT:0>])<EOL>
Return the centre of coordinates.

Parameters
----------
coordinates : numpy.ndarray
    An array containing molecule's coordinates.

Returns
-------
numpy.ndarray
    An 1d array with coordinates of the centre of coordinates excluding
    elements' masses.