AIPS HELP file for Y2K in 31DEC22
As of Fri Mar 24 4:02:18 2023
Y2K: Verification/timing test; see Y2KLOAD.001, Y2KEXEC.001
TCODE INIT, TEST, READ, or WRIT
TMODE T or M; Test or Master input
TMASK 1.0 127.0 test selection bit mask
Y2KSIZE SMALL, MEDIUM, LARGE test
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 1.0 9.0 Input/Output tape drive #.
Y2KDISK Disk area for READ and WRIT
EDGSKP 0.0 64.0 Pixels to skip at edges
TERSE -1.0 99.0 > 0 => reduced output
Printer disk file to save
BADDISK Disks to avoid
Type: RUN file
Use: Y2K performs the AIPS verification test on an AIPS system.
See RUN files Y2KLOAD.001 to compile a set of procedures and
Y2KEXEC.001 to run them. This input file is used to prepare the
parameters needed to run Y2KEXEC. Set the adverb values, do a
TPUT Y2K, and then RUN Y2KEXEC.
The idea is to run a sequence of the most commonly used tasks in
AIPS on a standard UV data set. The tasks are UVSRT, IMAGR,
APCLN, CALIB, and VTESS as the main tasks with tasks SUBIM,
COMB, UVDIF, CCMRG, FITLD, and FITAB also being exercised. The
test runs each task and compares the results with standard
answers prepared when the test was devised or last revised. The
total time it takes to execute may be used to compare computer
performance and the degree to which the current answers agree
with the official answers compares compilers/computers and code
TCODE String*4 'INIT' - create new master files
'TEST' - test tasks against master files
'READ' - read master files from tape/disk
'WRIT' - write master files to tape/disk
User sites would first READ the master files
in and then TEST them.
TMODE String*1 'T' - test output from previous task used as
input to next task.
'M' requests master input to all tasks.
TMASK Scalar Task selection bit mask (1-63) - use 63
+1=>SORT, +2=>IMAGR, +4=>APCLN, +8=>CALIB,
For example, TMASK=54 would execute all but
sort and CALIB.
Y2KSIZE String*8 'SMALL', 'MEDIUM', 'LARGE' test. The LARGE
test is used to measure performance. There
is also a 'HUGE' test.
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 or output tape drive #. (1-9)
Y2KDISK 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 -1 on all new or uncertain systems,
or when determining the AIPSMark(93).
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 Any bad disks to avoid for scratch files
VERSION String*48 Version of tasks to use - normally blank to
use TST. Other values include OLD, NEW, and
private dirs; use | to separate entries in a
Y2K 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. TEST steps use either the TEST run output
of the previous step (TMODE=T) or the INIT run
WRIT = write master or test files to tape (TMODE matters)
READ = read master files from tape.
Input data files for test steps are selected by the TMODE
adverb which has two possible values: 'T' for those made
in previous steps of the present test or 'M' for the
master "correct" data sets input from tape.
The adverb Y2KSIZE controls the size of the test performed:
'S' 512x512 image, 5000 clean components, 15000 vis
'M' 1024x1024 image, 15000 clean components, 75000 vis
'L' 2048x2048 image, 25000/75000 Clean components,
'H' 4096x4096 images, APCLN not used, 4-resolution IMAGR
used with 35000/200000 Clean components
Explanation of Y2K:
Y2K exercises important AIPS tasks using data for one of four
sources. The four data sets provide four sizes of "real" AIPS
reduction: 512x512 with 13000 vis. and 5000 components; 1024x1024 with
77000 vis. and 15000 components; 2048x2048 images with 425000 vis
and 25000/75000 Clean components and 4096x4096 images with a
4-resolution Clean on 2674490 vis with 35000 and 200000 Clean
components. The sources for the "small" problem was originally a
background sources for an HI absorption experiment by Liszt and
Greisen, the "medium" problem uses data supplied by Alan Bridle, and
the "large" and "huge" problems use data supplied by Rick Perley and
The Y2K tests are intended to certify the correct execution of all
AIPS systems. They are an enhancement of the DDT tests devised a
decade earlier for the same purpose on computers of more modest
capabilities. About DDT it was said: "The smallest is small enough to
run in less than one day on all machines which will ever run
AIPS." Its execution time is significant and easily measurable
on modest systems such as the Sparc IPX, and approximate timings
can also be obtained for faster systems. The AIPSmark(93) is
based on the total elapsed time for the Large DDT suite; see
AIPS memo 85 for full details. The AIPSmark(2000) has been defined in
AIPS Memo 104 using the large Y2K test in a similar manner. This memo
is available from our web site and is shipped with AIPS. The DDT test
used task MX extensively. That task was retired since it used image
projections which are no longer supported. Therefore the DDT test has
also been retired.
Steps to execute the Y2K 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 Y2KLOAD". This initiates the
compilation process, which on most modern systems will not take
more than a few minutes.
3. The next step is to read the data files from the tape, or from
disk. On tape, these are files 1 - 10 for the small problem, files
11 - 20 for the medium problem, and files 21 - 39 for the large
problem (which breaks the UV files into pieces). The HUGE test has
never been put on tape, a large-capacity tape would be required.
Alternately, if you have the files on disk, merely set the Y2KDISK
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). The Y2K
files are available via anonymous ftp to ftp.aoc.nrao.edu in
MGET Y2KL* (or Y2KS*, Y2KM*, Y2KH*)
On tapes, the first one in each set is the original visibility data
set of the Y2K problem. Subsequent files are the "master" versions
of files computed from the original dataset. The read process
consists of the following steps:
Specify DDISK, MDISK, TDISK, and IOTAPE or Y2KDISK
Also specify BADDISK as needed
Y2KSIZE='SMALL' or 'MEDIUM' or 'LARGE' or 'HUGE' (desired problem)
TPUT Y2K (TPUT saves adverb values)
MOUNT the tape unless you have the disk files
DISMOUNT the tape or remove/backup the disk files
PRTMSG (documents data read process)
In the case of a Y2K tape, the READ mode will rewind the tape
and skip over the data for the smaller problems (if 'SMALL'
wasn't given). It will then execute FITLD to read the UV and
image files to disk. At the end of the process, it rewinds
the tape and prints a directory of the disk files.
NOTE: Y2KEXEC 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 results are compared to the
master versions which were read from tape in the previous step.
There are two ways to perform the calculations: with each step
computed from the result of the previous test calculation in the
sequence, or else from the result of the previous MASTER
computation in the sequence. The first mode (TMODE='T') tests how
well the system under test is able to reproduce a complex sequence
of calculations beginning from a designated starting point. That
is, it measures the accumulation of error in the system. The
second mode (TMODE='M') tests the steps of the sequence separately
so that errors created in each step can be isolated. It is also
the step used for calculating the AIPSmark(2000). Both tests are
important, and both should be performed to certify fully the
scientific adequacy of an AIPS installation, but it is generally
best to use TMODE='M' as the initial (and primary) test of all
systems. The steps are:
CLRMSG (prepare for test results)
TCODE='TEST'; TMODE='M'; TMASK=63
Y2KSIZE='SMALL' or 'MEDIUM' or 'LARGE' (desired problem)
EDGSKP=4, 8, or 16 for small, medium or large/huge Y2KSIZE
TPUT Y2K (saves the adverb values)
PRTMSG (print out the test results)
For the AIPSmark values, TERSE should be set to -1. The message
file from Y2KEXEC will be more than 2000 lines long. It is
intended to be the major item documenting the test procedures and
results. We usually test with messages coming to the xterm running
the test - in other words, we kill the message server if one comes
Making a second run with TMODE='T' is not required, but it may be
advisable to evaluate the accumulation of error. This process also
checks the manipulations of visibilities, antenna files, and gain
files; these processes are not really tested in the 'M' mode
because AIPS currently has no comparison operators for files of
these types. The 'T' mode tests them by their effect on subsequent
map results. This is particularly important for the output of the
self-calibration program CALIB.
One can also rerun the tests with a different value for the
VERSION adverb. One can also use this option to test
experimental versions of specific tasks.
In the HUGE tests, the accuracy of the residual images after the
first Clean is not as good as that of the other steps. This is
normal and should not be a great concern.
Typical inputs look like
Y2K : Verification/timing test; see Y2KLOAD.001, Y2KEXEC.001
Adverbs Values Comments
TCODE 'TEST' INIT, TEST, READ, or WRIT
TMODE 'M' T or M; Test or Master input
TMASK 63 test selection bit mask
Y2KSIZE 'LARGE ' SMALL, MEDIUM, LARGE test
DDISK 2 Disk drive #: master UVDATA
MDISK 2 Disk drive #: other masters
TDISK 2 Disk drive #: test images
IOTAPE 1 Input/Output tape drive #.
Y2KDISK 'MYY2K ' Disk area for READ and WRIT
EDGSKP 4 Pixels to skip at edges
TERSE -1 > 0 => reduced output
OUTPRINT 'FITS:Y2K.15Jan05 '
Printer disk file to save
BADDISK *all 0 Disks to avoid
VERSION ' '
where environment variable MYY2K is the data area used for the FITS
disk files for Y2K data.
A typical number of bits looks like:
'IMAGE' 13.1018839 15.531579
'IMBEAM' 13.8289413 16.6617813
'APCLN' 12.7427092 16.7804108
'APRES' 17.8541603 24.5266685
'IMCLN' 9.6245136 16.6369858
'VTESS' 15.2701616 23.2641563
'VTESSC' 16.6828175 20.8412228
The important timing lines are:
15:18:41 AIPS run y2ke
15:33:42 AIPS 'PRINTING MESSAGES SUGGESTIVE OF ERROR: PRIO > 5'
giving 15:01 seconds elapsed time (901 sec or aipsmark 44)
The PRTAC information summary confirms
# tasks 20
Tot real 14.9
Tot cpu 10.231
Av cp/re .41414
the total real time and shows that the cpu/real performance of this
machine was not particularly good.
5. The 'WRIT' mode tests task FITAB, while 'READ' tests FITLD. The
basic idea is to produce a tape (or FITS disk files), and then to
read that tape or those files 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 Y2K on it! This verifies the
intercommunication of the systems. Obviously, use of FITS disk
files will do little to test your tape I/O.
Note that Y2K assumes that the tape consists of the 10 SMALL data
files, followed by 10 MEDIUM data files, followed by 10 LARGE data
files. You should first run Y2K in WRIT mode for the SMALL
problem. If generating a tape, having done this, you may then
(optionally) run Y2K in WRIT mode for the medium problem and,
having done all this, you may then WRIT the LARGE problem.
The steps are:
Y2KSIZE='SMALL' or 'MEDIUM' or 'LARGE' (desired problem)
PRTMSG (print out the test results)
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 Y2KDISK 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 (Y2Ksnnnnnn,
where s is S, M,or L and nnnnnn is the image name related to the
task name). The LARGE test divides the UV data files into "pieces"
as defined by FITAB.
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. Y2K 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 file.
In TEST mode, the listing produced by PRTAC will show only the last
sequence of tasks suitable for the Y2K test. In other modes, it
will list all tasks run in the last day or two. 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
It is obvious that Y2KLOAD and Y2KEXEC are cloneable. First, a
clone of Y2K could process another dataset; this would be done
by adding additional allowed string values for Y2KSIZE and
renaming the input UV data set DY2K?, where ? is the first
character in the new allowed string value. The adverb values
needed for the new data set, are initialized in the Y2KPROC
procedure which is SAVEd in Y2KSAVE. Second, the general
pattern of executing and testing the tasks in succession will
work for a wide variety of AIPS tasks and data types.
Interpretation of Test Results
The results of the mapping 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.
For further information on the interpretation of the results, refer to
AIPS memo 85, 104, and other memos in the AIPS memo series that relate
to the Y2K tests. These are available via anonymous ftp and the world
wide web on the internet; ftp to ftp.aoc.nrao.edu, cd to
pub/software/aips/TEXT/PUBL/ . The web page is