As of Wed Jun 3 1:16:58 2020

VLAL: Calibration verification/timing test for spectral line


TCODE                              INIT,TEST,READ, or WRIT
TMODE                              'T' or 'M' inputs
TMASK           1.0       255.0    test selection bit mask
DDISK           1.0        35.0    Disk drive #: master UVDATA
MDISK           1.0        35.0    Disk drive #: other masters
TDISK           1.0        35.0    Disk drive #: test images
IOTAPE          0.0        35.0    Input/Output tape drive #.
DDTDISK                            Disk area for READ and WRIT
EDGSKP          0.0        64.0    Pixels to skip at edges
TERSE          -1.0        10.0    > 0 => reduced output
DOCRT          -1.0       132.0    > 0 => output on terminal
                                   > 72 => width of terminal
                                   Printer disk file to save
BADDISK         0.0        35.0    Disks to avoid


Type: RUN file
Use:  VLAL performs the AIPS verification test for spectral line
      calibration and imaging software.
      See RUN files VLALLOAD.001 and VLALEXEC.001.  The purpose
      of the inputs file is to perform bounds checks on the
      parameters and to enable the use of TPUT and TGET.
 TCODE    String*4      'INIT', 'TEST', 'READ', or 'WRIT'
 TMODE    String*1      'T' or 'M' inputs for SPLIT, VLAL
 TMASK    Scalar        test selection bit mask (1-127)
 DDISK    Scalar        Disk drive # (1-9) master UVDATA
 MDISK    Scalar        Disk drive # (1-9) other master files
 TDISK    Scalar        Disk drive # (1-9) test files
 IOTAPE   Scalar        Input AND output tape drive #. (1-9)
 DDTDISK  String*8      Logical name of disk area to be used for
                        FITS-disk files in READ or WRIT instead
                        of actual magnetic tape.
                        ' ' => use magnetic tape.
 EDGSKP   Scalar        Number of pixels to skip at edges in
                        comparing test and master images
 TERSE    Scalar        > 0 => reduced output:
                          > 0 = drops INPUTS for all tasks and
                                TPHEAD when reading tape
                          > 2 = also drops CATALOG listings
                          > 3 = also drops IMHEADER listings
                        Use 0 on all new or uncertain systems.
 DOCRT    Scalar        <= 0 -> print the messages and output
                           from tasks on the line printer.
                        > 0 -> show the messages and output from
                           tasks in slightly abbreviated form on
                           the terminal.  If you have a wide
                           terminal, set DOCRT to its width in
                           characters for a more complete
 OUTPRINT String*48     Disk file name in which to save the line
                        printer output.   ' ' => use scratch and
                        print immediately for interactive jobs -
                        batch jobs use OUTPRINT =
                        'PRTFIL:BATCHjjj.nnn' (jjj = job #, nnn
                        = user #).  When OUTPRINT is not blank,
                        multiple outputs are concatenated and
                        the file is not actually printed.
 BADDISK  Array         Disks to avoid for scratch files.
                        (also private dirs; use | to separate)

VLAL runs in four different modes: (TCODE)
   INIT = starts from the original master UV dataset, and
           (re)computes master files (does ALLDEST).
           The "mask" TMASK controls which steps execute.
   TEST = re-does the INIT computation but stores the new
           files under different names and compares against
           masters. The "mask" TMASK controls which steps
           execute.  For the early, table manipulation steps,
           the TEST mode can only operate on the output of the
           previous step and step 1 must be run first.  For the
           SPLIT and VLAL tests either the TEST run
           output of the previous step (TMODE=T) or the INIT run
           output (TMODE=M) can be used as input.
   WRIT = write out all master files to   tape.
   READ = read  in  all master files from tape.

A binary mask controls which steps of the test execute:
         +16=>GETJY,CLCAL, +32=>BPASS, +64=>SPLIT, +128 =>IMAGR
   For example, TMASK=54 would execute AVSPEC, UVFLG,SETJY, GETJY,
                 CLCAL, and BPASS.
Note: the UVCOP step is required once create the input file for
the following steps for TCODE='TEST'.


Explanation of VLAL:               (DOSW Jan91)

VLAL is designed to verify the correct functioning of the
spectral line calibration using a test set of VLA observations.  All
of the typical steps in editing and calibrating a set of
line (non-VLBI) are exercized except for interactive
editing. Since most of these operations modify only tables, a
comparison of selected portions of various of the calibration
tables is made. After the calibration tasks are completed, the
data are calibrated using SPLIT and the uv data are compared with
the master version.  The final test is a comparison of VLAL images
made from the calibrated data.
Steps to execute the VLAL Test on a new computer:

1. Log in to AIPS under the user number which will own the data
   files and the SAVE/GET files associated with the test.  It is
   probably convenient to clear your AIPS message file before
   proceeding: PRNUM=-1; (PRTMSG possibly) ; CLRMSG

2. Now do the POPS command "RUN VLALLOAD". This initiates the
   compilation process, which can take as long as 15 minutes on
   a heavily loaded VAX-11/780. You may want to execute the POPS
   command "PRTMSG" afterwards to document the compilation of
   the test procedures.

3. The next step is to read the data files from the tape.  There
   are 6 files for this test.  The read process consists of the
   following steps:
      CLRMSG                       (prepare for tape read steps)
      Specify DDISK, MDISK, TDISK, and IOTAPE
      Also specify BADDISK as needed
      DDTDISK = ' '  for real tapes
      TCODE='READ'; TPUT VLAL         (TPUT saves adverb values)
      MOUNT the tape
      DISMOUNT the tape
   The READ mode of VLAL will execute UVLOD and IMLOD in the
   appropriate pattern to read the UV and map files to disk.  At
   the end of the process, it rewinds the tape and prints a
   directory of the disk files.

   Alternately, if you have the files on disk, merely set the DDTDISK
   adverb to point at where the files reside (you need to define or use
   a "logical" or environment variable with an uppercase name before
   starting AIPS to use this feature; e.g. FITS).

   NOTE: VLALEXEC will insist on having non-default values for

4. Now it is time to actually perform the test.  The 'TEST' mode
   recomputes the various files.  All map, uv data and selected
   calibration table results are compared to the master versions
   which were read from tape in the previous step. The steps
      CLRMSG                       (prepare for test results)
      TCODE='TEST'; TMASK=255
      TPUT VLAL                     (saves the adverb values)
   The message file from VLALEXEC will be more than 2000 lines
   long.  It is intended to be the major item documenting the
   test procedures and results.  Several tasks will print
   results rather than put them in the message file.
   Especially, the LISTR output should be checked.

5. The 'WRIT' mode tests task FITTP, while 'READ' tests FITLD.  The
   basic idea is to produce a tape, and then to read that tape on an
   AIPS system to verify that it yields correct results.  It follows
   that generating a new tape with the 'WRIT' mode and then executing
   'READ' and 'TEST' on it will also effectively test the tape tasks.
   Better yet, take the tape to another AIPS and run VLAL on it!  This
   verifies the intercommunication of the systems.  The steps are:
      TCODE='WRIT'; TMASK=255

   Note that when we say "tape", we mean either magnetic tape in the
   usual sense, or pseudo-tape disk files.  The latter are selected by
   setting DDTDISK to a non-blank value which is the logical name
   (environmental variable) for the disk area to be used.  The disk
   files are given a fixed and obvious pattern of names (VLALnnnnnn,
   where nnnnnn is the image name related to the task name).

6. Finally, one wants to know the accounting statistics from the
   test runs.  The accounting listing can be correlated with the
   message file listings in order to analyze the performance of
   the tested system.  VLAL now runs task PRTAC to produce the
   desired information.  Note that PRTAC has exclusive access to
   the accounting file until it finishes, and so various tasks
   may complain while they are waiting to get access to the

   The listing produced by PRTAC will have one line for each
   execution of any task or program AIPS.  The columns of the
   listing give the taskname, POPS#, user#, start-time, real-
   time, CPU-time, and "IOCNT".  Asterisks mark any run that
   aborted.  After this basic sequential listing comes a listing
   by task name giving the totals accumulated by each task.  The
   listing is given in two sort orders.

   The tasks tested in some modes are:
   and COMB

               Description of Data Calibration Test

   The test data set consists of observations of a the OH maser
source W3(OH), 3c286 (for flux and bandpass calibration) and
phase calibrator.  The observation lasts 1 hour, using the 2AC mode
with two diferent frequencies: 1665 and 1667 MHz.  These appear as
FREQID 1 and FREQID 2 in the uvdata files.

The data were obtained with the VLA in "C" configuration at 18 cm
wavelength, 32 channels of 6.104kHz each (On-line hanning smoothing).

The master copies of the files were computed on a prerelease version
of 15JAN91 AIPS running on a SUN SPARCstation 1 (SPECTRA).

   The following sections describe in some detail the tasks run
in each of the test steps.  Only the test mode is described;
READ, WRIT and INIT modes are fairly obvious given the TEST mode

Step 1.  The master uv data file is copied to a test version
using UVCOP.

Setp 2.  AVSPC is used to create a channel 0 image from the AIPS
uvdata files to see if they agree with the channel 0 file created
by the on-line system.

Step 4.  Bad data is flagged with several runs of UVFLG.  The
fluxes in the SU table are reset and the flux of 3C286 set using

Step 8.  CALIB is run on 3C286 and the phase calibrator.  The SN
table is sorted using TASRT and the tables are copied using
TASAV.  The comparison of the SN tables is done using the TASAV

Step 16.  GETJY is used to estimate the flux density of the phase
calibrator and corrects the SN table.  CLCAL then filters the SN
table with a 1.1 hour median window filter on the amplitudes and
writes CL table 2.  Comparisons are made of the SU and CL #2

Step 32.  BPASS is run to determine the bandpass response.

Step 64.  SPLIT is used to apply the calibration and editing
tables to the source data and write a single source output file.
This file is compared with the master.

Step 128.  VLAL  is run on the output of SPLIT to make I and Q
images.  Comparisons are made of the I image, I beam and the Q

                Interpretation of Test Results

The results of the mapping and table tests are recorded as the
number of BITS of accuracy.  The BITS of accuracy are defined in
two ways, by the MAX difference in the Master image and the Test
image and by the RMS differences in the images.  The BITS
measured by the the base 2 logarithm of the ratio of PEAK and
DIFFERENCE of the images.

The BITS are calculated as -3.3219 * LOG(DIFF/PEAK).
(LOG is the Base 10 Logarithm; 1/LOG(2) = 3.3219)

The expected BITS of accuracy for the tasks are in the
range of 10 to 20 BITS.  The RMS BITS of accuracy is
always greater than the PEAK BITS of accuracy.  Perfect
agreement will be reported as 99 bits agreement.

Note that some of the operations in this test modify the input
file(s).  This especially true for the table operations and in
particular GETJY may recursively modify the SU and SN tables.
This may cause roundoff errors to accumulate.  For the most
accurate test, all of the steps must be run in order exactly
once each (i.e. use TMASK=127).

Note also that the uv data is stored in compressed form meaning
that it has at most 15 bits of precision rather than the 24-25
(usually) for floating point.

There are three kinds of test made of agreement with the master
1) UV data sets are compared using UVDIF which reports on
individual visibility records with differences larger than the
threshold.  The statistics of the data being checked are also
2) Images are differenced and the statistics of the difference
image is reported both as the test is done and in the summary at
the end.
3) Selected portions of calibration tables will be compared with
the master version and differences are reported in a manner
similar to that for images.

   The following describes the comparison tests between tables,
uv data and images.  The column labeled "Test" gives the label
used in the summary given at the end of the execution of

Test        Type                 Comments
__________  ____ ______________________________________________
AVSPEC      uv   The on-line vs. AVSPC CH0 uvdata are compared.

CALIB SN 1  tab  The solution for FREQID 1 is compared.

CALIB SN 2  tab  The solution for FREQID 2 is compared.

GETJY       tab  I flux from SU table determined by GETJY.
		 FREQID 1 and 2 must be handled separately
                 because the SU table does not have separate
                 entries for FREQID 1 and 2.

CLCAL CL 1  tab  Results for FREQID 1.  Every 25th
                 element of the table is compared.

CLCAL CL 2  tab  Results for FREQID 2.  Every 25th
                 element of the table is compared.

BPASS BP 1  tab  Results for FREQID 1.  Every 25th
                 element of the table is compared.

BPASS BP 2  tab  Results for FREQID 2.  Every 25th
                 element of the table is compared.

SPLIT       uv   The output of SPLIT is compared.

VLAL IMAP  map  The I images from VLAL are compared.

VLAL IBEM  map  The I beams from VLAL are compared.