def matrixTimesVector(MM, aa):
    """

    :param MM: A matrix of size 3x3
    :param aa: A vector of size 3
    :return: A vector of size 3 which is the product of the matrix by the vector
    """
    bb = np.zeros(3, np.float)
    for ii in range(3):
        bb[ii] = np.sum(MM[ii, :] * aa)
    return bb
def matrixTimesVector ( MM , aa ) : bb = np . zeros ( 3 , np . float ) for ii in range ( 3 ) : bb [ ii ] = np . sum ( MM [ ii , : ] * aa ) return bb
:param MM: A matrix of size 3x3
    :param aa: A vector of size 3
    :return: A vector of size 3 which is the product of the matrix by the vector