def strictly_monotonic(bb):
    '''
    bb is an index array which may have numerous double or triple
    occurrences of indices, such as for example the decay_index_pointer.
    This method removes all entries <= -, then all dublicates and
    finally returns a sorted list of indices.
    '''
    cc=bb[np.where(bb>=0)]
    cc.sort()
    dc=cc[1:]-cc[:-1]
    dc=np.insert(dc,0,1)
    dc_mask=np.ma.masked_equal(dc,0)
    return np.ma.array(cc,mask=dc_mask.mask).compressed()