docs: def velocity_dispersion(self, kwargs_lens, kwargs_lens_light, lens_light_model_bool_list=None, aniso_param=1,
                              r_eff=None, R_slit=0.81, dR_slit=0.1, psf_fwhm=0.7, num_evaluate=1000):
          """
          computes the LOS velocity dispersion of the lens within a slit of size R_slit x dR_slit and seeing psf_fwhm.
          The assumptions are a Hernquist light profile and the spherical power-law lens model at the first position.
  
          Further information can be found in the AnalyticKinematics() class.
  
          :param kwargs_lens: lens model parameters
          :param kwargs_lens_light: deflector light parameters
          :param aniso_param: scaled r_ani with respect to the half light radius
          :param r_eff: half light radius, if not provided, will be computed from the lens light model
          :param R_slit: width of the slit
          :param dR_slit: length of the slit
          :param psf_fwhm: full width at half maximum of the seeing condition
          :param num_evaluate: number of spectral rendering of the light distribution that end up on the slit
          :return: velocity dispersion in units [km/s]
          """
          gamma = kwargs_lens[0]['gamma']
          if 'center_x' in kwargs_lens_light[0]:
              center_x, center_y = kwargs_lens_light[0]['center_x'], kwargs_lens_light[0]['center_y']
          else:
              center_x, center_y = 0, 0
          if r_eff is None:
              r_eff = self.lens_analysis.half_light_radius_lens(kwargs_lens_light, center_x=center_x, center_y=center_y, model_bool_list=lens_light_model_bool_list)
          theta_E = kwargs_lens[0]['theta_E']
          r_ani = aniso_param * r_eff
          sigma2 = self.analytic_kinematics.vel_disp(gamma, theta_E, r_eff, r_ani, R_slit, dR_slit, FWHM=psf_fwhm, rendering_number=num_evaluate)
          return sigma2