def mat333mult(a, b):
    """
    Multiply a 3x3 matrix with a 3x1 matrix.
    
    Parameters
    ----------
    a : tuple of tuple of float
		3x3 matrix
    b : tuple of tuple if float
		3x1 matrix
		
    Returns
    -------
    res : list of float
		3x1 matrix
    """
    res = [0, 0, 0]
    r3 = range(3)
    for i in r3:
        res[i] = sum([a[i][j]*b[j] for j in r3])
    return res