def z_axis_rotation(theta):
        """Generates a 3x3 rotation matrix for a rotation of angle
        theta about the z axis.

        Parameters
        ----------
        theta : float
            amount to rotate, in radians

        Returns
        -------
        :obj:`numpy.ndarray` of float
            A random 3x3 rotation matrix.
        """
        R = np.array([[np.cos(theta), -np.sin(theta), 0],
                      [np.sin(theta), np.cos(theta), 0],
                      [0, 0, 1]])
        return R
Generates a 3x3 rotation matrix for a rotation of angle
        theta about the z axis.

        Parameters
        ----------
        theta : float
            amount to rotate, in radians

        Returns
        -------
        :obj:`numpy.ndarray` of float
            A random 3x3 rotation matrix.