code: def vel_disp(self, gamma, theta_E, r_eff, r_ani, R_slit, dR_slit, FWHM, rendering_number=1000):
          
          sigma_s2_sum = 0
          rho0_r0_gamma = self._rho0_r0_gamma(theta_E, gamma)
          for i in range(0, rendering_number):
              sigma_s2_draw = self.vel_disp_one(gamma, rho0_r0_gamma, r_eff, r_ani, R_slit, dR_slit, FWHM)
              sigma_s2_sum += sigma_s2_draw
          sigma_s2_average = sigma_s2_sum / rendering_number
          return np.sqrt(sigma_s2_average)
docs: computes the averaged LOS velocity dispersion in the slit (convolved)
  
          :param gamma: power-law slope of the mass profile (isothermal = 2)
          :param theta_E: Einstein radius of the lens (in arcseconds)
          :param r_eff: half light radius of the Hernquist profile (or as an approximation of any other profile to be described as a Hernquist profile
          :param r_ani: anisotropy radius
          :param R_slit: length of the slit/box
          :param dR_slit: width of the slit/box
          :param FWHM: full width at half maximum of the seeing conditions, described as a Gaussian
          :param rendering_number: number of spectral renderings drawn from the light distribution that go through the
              slit of the observations
  
          :return: LOS integrated velocity dispersion in units [km/s]