def rot3(theta):
    """
    Args:
        theta (float): Angle in radians
    Return:
        Rotation matrix of angle theta around the Z-axis
    """
    return np.array([
        [np.cos(theta), np.sin(theta), 0],
        [-np.sin(theta), np.cos(theta), 0],
        [0, 0, 1]
    ])