Example for the full spectrum fitting of the spectrum of a BCG. The green, blue, and red lines in the top left panel represent the observed spectrum (O_λ), its error spectrum, and the model spectrum (M_λ), respectively. The residual spectrum (E_λ) is shown by the purple line in the bottom left panel. In the left panels, both O_λ and M_λ are scaled by normalizing the flux at wavelength 4020 Å  to 1. The light-weighted and the mass-weighted fractions of stellar populations, i.e., x_j and μ_j, are shown in the top and the bottom right panels, respectively. Several quantities (see Sect. 3) derived from the fitting are listed in the top right corner.