Left: Eigen spectra of thirteen principal components with percentage of variances as well as uncertainties (2σ), toward W3(OH). Right: scaled channel-wise column density spectra for the thirteen species (HCO⁺, HCN, HNC, CS, H₂S, C₂H, c-C₃H₂, CH, OH, O, C⁺, H₂O⁺, and OH⁺) as a function of v_LSR. Black curves represent the observational data, and red dotted curves are the spectra reproduced with only the first three principal components (PC-1, PC-2, and PC-3). For C⁺, H₂O⁺, and OH⁺, the reproduced spectra indicated by blue dotted curves include one or two more PCs, i.e., PC-4 and PC-5.