Computational details
The FT-IR spectra of all studied oil samples were collected in a
data matrix D of the dimension of (255 nw), where nw is the
number of wave number for each samples. Thus, each row of D
(di) is the FT-IR spectrum of a specified sample. The data were
auto-scaled to zero mean and then were also subjected to extended
multiplicative signal correction (EMSC) if necessary.