[daip] Test of VBMRG

[Jon Romney]

I am testing an ancient task, VBMRG, originally written
to combine and select unique visibilities from multiple
correlation passes with subsets of observing stations
-- on the NRAO *Mark 2* correlator.

This same capability is now a near-future need for the
VLBA correlator, as our data playback capacity completes
its shrinkage from 20 tapes to perhaps 12 Mark 5s.  The
objective of the tests is to see whether VBMRG is able
to handle VLBA correlator data, and if not to get some
idea of the effort involved to make it so.

I'm using data from a fairly routine HSA observation,
BK114F.  I had three correlation passes done, each with
a different 10-station subset of the total 13 stations.
The test data have eight single-polarization IFs of 256
spectral channels each.

After several false starts, and based on advice from
Eric, I did the following --

--  Load all three passes sequentially using FITLD, with
concatenation ON and compression OFF.  This seemed to
work.  Output dataset: STNSUBTEST.UVDATA.1.

--  Sort into BT order using MSORT.  It notes a "Truely
brute force disk copy to be done", but also "Appears to
have ended successfully".  Output dataset:
STNSUBTSRT.UVDATA.1.

--  Run VBMRG on the sorted dataset.  This failed, with
error message: "RECORD LENGTH=  6154 GREATER THAN  2060 /
VMRGUV: VMERGE ERROR  8".

The datasets mentioned above are on 'thuban' disk 2,
user #1891.

Thanks,
Jon