Conclusion

In this document we fully described the current status of the ACCUMULATE and AVERAGE commands of CLASS, applied on spectra. They are very often used, and for different purposes, e.g. averaging a set of spectra or concatenating them. User must be warned about several traps that he may encounter:

• averaging a set of spectra with successive calls to AVERAGE may lead into different results than averaging the whole set with a single call to the command,
• averaging non-aligned spectra must invoke at one point a resampling. User can do it himself or rely on the internal resampling loops of the commands. The resampling has non-trivial effect of the weights.

As a solution to the first problem, the question of saving a weight array (one weight per channel) in the CLASS data format has been raised. This would have consequences in particular in term of disk storage.