C.2 Table Philosophy

AIPS follows an incremental calibration process on multi-source data sets. Calibration solutions are written to SN (“Solution”) tables, which can be inspected in various ways. CLCAL is used to apply an SN table and write a new CL (“Calibration”) table, which stores the cumulative calibrations. If the procedure in VLBAUTIL is used, much of this is hidden, however most procedures will report the new SN andor CL that are produced. The actual visibilities are not altered until the final calibration is applied using SPLIT (or SPLAT), which produces single-source (or multi-source) data sets that can be imaged. With this philosophy, it is easy to back up a step or two if errors are made in processing. Users should keep track of which tables contain which solutions and calibrations as they go through the calibration process.

A key verb to be aware of is EXTDEST, which can delete any unwanted table. For example, to delete SN version 3 from the data set cataloged as data set 1 on disk 1, type INDISK 1; GETNAME 1; INEXT ’SN’; INVER 3; INP EXTDEST; EXTDEST. Beware of the fact that once a table is deleted, there is no ‘undelete’ function.