This is the path to the file to read in, as a quoted string.

number of lines at the top of the file before the data begins

number of columns the data

a vector saying how many rows are in each of the matrices of spectra in the file; for instance nrows = c(256,256,256) would indicate that the file stores spectra associated with 3 datasets, each of which contains 256 wavelengths. If nrows is not given, then a single file containing all data is writen.