def calc_rDsq(H, A):
    """needs doc string"""
    rdsq = H[0] * H[0] * A[0] + H[1] * H[1] * A[1] + H[2] * H[2] * A[2] + H[0
        ] * H[1] * A[3] + H[0] * H[2] * A[4] + H[1] * H[2] * A[5]
    return rdsq
