AIPS HELP file for VLAL in 31DEC20
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.
VERSION String*48 OLD,NEW,OLDPSAP,NEWPSAP,LOCAL
(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:
TMASK +1=>UVCOP, +2=> AVSPEC, +4=>UVFLG,SETJY, +8=>CALIB,
+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
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
IOTAPE, DDISK, MDISK, and TDISK.
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)
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:
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:
UVCOP, TABED, UVFLG, SETJY, CALIB, TASRT, TASAV, GETJY,
CLCAL, PCAL, TACOP, CLCOR, LISTR, SPLIT, UVDIF, IMAGR,
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
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
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.