Keywords: class-average

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# 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.