[daip] AIPS handling of weights and flags

[Eskil Varenius]

Dear AIPS support,
I wonder about how AIPS handles weights and flags. Please direct me to the
appropriate place if this address is not the correct one. I've searched the
net, cookbook and explain-pages without a clearcut answer. I would be very
happy if someone could increase my knowledge around the following questions.

What is the meaning of negative weights for visibilities? Is there a
general way in which such visibilities are handled throught AIPS?
Suppose that I modify weights on some visibilities using WTMOD (or
ParselTongue) to -1. If I then use the task FIXWT to modify weights to
reflect the amplitude scatter of data, will this also modify the negative
weights? Or, will it only modify positive weights?

Finally I wonder about SPLIT. SPLIT can apply an FG-table. If I make a
single-source file using SPLIT from a multi-sourcefile, and chose to flag
data using the multi-sourcefile-FG-table, will SPLIT remove every single
flagged visibility? Or - since I don't see any FG table in the produced
single-source file - are some visibilites still transferred for some reason
but with modified weights? What about visibilites with negative weigths,
will these count as flagged when using SPLIT?

Best regards,
Eskil Varenius
PhD student
Onsala Space Observatory
Chalmers University of Technology
Sweden
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