The AVERAGE algorithm is based on a single run through the whole index. The spectra are averaged two by two, each output sum becoming an input spectrum when adding the next observation of the index.
This incremental method requires to associate a weight to the output/input sum, in concordance with the number and weights of the spectra already summed. Furthermore, this weight must be an array (one weight per channel), because the command allows to combine different spectra with different range of frequencies (e.g. COMPOSITE mode), i.e. not the same number of spectra may have contributed to each channel in the output sum.
The ACCUMULATE algorithm uses the same code but adds only two input
spectra (
and 
).
The algorithm described here apply only on spectra. The average of continuum drifts rely on specific routines which are not considered here.