Experimental "CVX" AIPS

For about one and a half years, I was "disinvited" from working on the Classic AIPS project, which was directed during that period by various individuals at the Array Operations Center in Socorro, New Mexico. During my diaspora, I continued to develop AIPS-based software in a private version called CVX for Charlottesville experimental. In mid October, 1997 I was invited to rejoin the "official" Classic AIPS project and my CVX code was installed in its entirety as the 15APR98 version of AIPS. See below for details of these unanticipated developments. My recent software efforts, plus contributions made by others in the Classic AIPS Group to 15APR98, are described below in sections containing reasons to choose 15APR98 or 15OCT97 versions (last updated 7 January 1998), poster and paper for ADASS 1997 (last updated 4 September 1997), detailed information on new and improved programs (last updated 7 January 1998),

The "CVX" ("Charlottesville Experimental") version of AIPS has been renamed the 15APR98 version. I have kept up with changes in the older versions as much as possible and have developed new algorithms or other interesting improvements. I have changed basic bits of infrastructure in the AIPS code, so please be cautious when using the 15APR98 version. Bugs are to be expected.

The 15APR98 version uses somewhat revised data formats from the older versions. It is able to read and convert headers and BP tables written by the older versions, but the older versions CANNOT handle data written by 15APR98. The adverbs have changed enough that SAVE/GET files are also not interchangeable. Through a clever trick, 15APR98 is able to read older SAVE/GET files, but the older versions are unable to read 15APR98's files. Also, NEW/OLD tasks may not be started from 15APR98 aips and 15APR98 tasks may not be started from NEW or OLD aips. (The 15APR98 one is larger and forced changes in the task-communication file.) The TV displays are no longer compatible; the one in 15APR98 has improved communication methods and the image catalog and TV description files have been eliminated. IN SUMMARY, ONCE YOU START USING 15APR98 YOU MUST FORGET ABOUT EARLIER RELEASES.

The 15APR98 version of AIPS is no longer available. It has been further enhanced and corrected and appears as 15OCT98 in a frozen form. Still more development has taken place and is available to advernturous sites as the 15APR99 release. See the main AIPS home page for further details.

[15APR98] Should I use 15APR98 or 15OCT97 Classic AIPS?

* Use 15OCT97 for reliability
  1. 15OCT97 is asserted to be very reliable due to its cautious development plan.
  2. 15OCT97 is used by a substantial number of VLA and VLBA observers at the AOC and other midnight job sites (CIT, CfA, MPI) further improving its reliability.
  3. It is the official, frozen and released NRAO AIPS.
* Use 15APR98 for VLA imaging and calibration
  1. Images may be made (and used as models) with each field tangent to the Celestial sphere at its center. This allows larger fields at greater distances from the original tangent point than can be imaged correctly in 15OCT97. This new capability is essential at P Band.
  2. The same source may be Cleaned from more than one field without compromising the convergence of Clean using a new sequence of imaging/Cleaning.
  3. Clean components from each field may be restored to any field in which they lie. Previous Cleans restored components only to that field in which they were found.
  4. 15APR98 allows 64 fields rather than the 16 limit in 15OCT97.
  5. The fields may be re-gridded after Cleaning onto a single large image centered on the pointing direction.
  6. Data may be weighted more correctly using calibrated Tant values.
  7. UV data may be edited on the contents of system temperature and gain solution tables using the interactive task EDITA (developed in 15APR98, now copied to 15OCT97). The Tsys editing appears to be all the editing required by VLA data.
  8. The 15APR98 version of CALIB has flexible options for measuring and reporting closure problems not available in 15OCT97.
  9. The 15APR98 version of UVSUB has an option to write out a file of the source model evaluated at the input data samples.
  10. 15APR98 DBCON does a correct phase shift when correcting different coordinates, accounting for frequency efficiently in all modes (for single-source data) and prevents errors when coordinate differences are found in multi-source data.
* Use 15APR98 for VLA spectral-line calibration
  1. The changes made to the computation of the bandpass table and its application have allowed "seamless stitching" of overlapped IFs. This has never worked before and implies a substantial improvement in the quality of the calibration.
  2. Errors in handling large numbers of channels and IFs, in handling the BCHAN, ECHAN, and STOKES options, and in re-referencing the phases to a common antenna have been corrected.
  3. Closure errors in bandpass solutions have been found to be the major source of spectral problems in line imaging. 15APR98 has flexible tools for measuring and reporting these, not available in 15OCT97.
  4. Bad data may be flagged with a multi-source file version of UVLIN called UVMLN. Preliminary bandpass and other calibrations are applied, a linear baseline is fit, and flags generated for those spectra having excess residuals in the baseline-fit channels.
* Use 15APR98 for VLBA imaging and calibration
  1. The 15APR98 version of SCMAP allows iterative imaging and self-calibration with interactive editing of the data at each self-cal. Both the input and residual data are shown with up to 10 selected baselines to the selected antenna being displayed on the TV. An earlier copy of 15APR98's SCMAP was taken for 15OCT97, but it lacks recent corrections and a significant enhancement to the flexibility of amplitude as well as phase self-cal.
  2. The same interactive editing is also available in task EDITR.
  3. 15APR98 allows up to 50 extension file types; 15OCT97 is limited to 20.
  4. On operating systems which allow for very large files (currently only DEC Alphas, SGI and Solaris 2.6), 15APR98 will allow you to make files as large as your file system will hold. Files on other systems are limited to 2 Gbytes.
  5. The 15APR98 versions of VPLOT, CLPLT, and IBLED compute models correctly and support the 3D imaging option. The 15OCT97 versions have an error in the model computation and CLPLT does not read the data correctly.
  6. All VLB-related improvements made in the 15OCT97 version are ported to 15APR98. They have now been thoroughly tested and were found to need only very minor corrections.
  7. 15APR98 UVCOP allows the application of a flag table.
* Use 15APR98 for spectral-line single-dish imaging
  1. Circular gridding functions have been corrected.
  2. 12m data may now be read all IFs at once with time interpolation of the applied gains and offs.
  3. 12m data may be indexed.
  4. Spectral data may be corrected to the desired velocity as a function of time and pointing.
  5. Spectral baselines may be removed from 12m data before imaging with or without averaging all IFs at each time.
  6. Imaging requires less disk space in 15APR98 than in 15OCT97.
  7. Any number of separate images may be combined with correct weighting.
* Use 15APR98 for continuum single-dish imaging
  1. 12m beam-switched continuum on-the-fly data may now be read into AIPS including all IFs at once.
  2. These data may be imaged and corrected using the convolutional methods initially described by Emerson et al.
  3. This experimental form of imaging may also be tested with modeling and test programs.
* Use 15APR98 for remote computing
  1. The 15APR98 TV display manages the data describing the display and its current state and contents. Separate computers running 15APR98 can thereby correctly drive and read back from the same display even if they do not have similar architectures and cannot share disk files. The problem of locking this display from multiple use has been solved.
* Use 15APR98 for corrected and improved tasks
  1. SPECR which resamples (in frequency) spectral uv data, FIXWT which estimates correct uv weights from the rms of the data, and DTSUM which summarizes data set contents have all been corrected in substantial ways.
  2. PRTAB was given new adverbs to allow flexible control over which parts of a table are displayed and which ignored.
  3. OGEOM handles blanks and edges much better than LGEOM and is only in 15APR98.
  4. SERCH is a new task to find weak line signals in spectral-line image cubes using algorithms developed by Juan Uson.
  5. The year 2000 problem has been addressed in 15APR98; unnecessary problems encountered by unregistered sites and excess delays on faster computers have been corrected in 15APR98.
  6. 15OCT97 INDXR cannot handle multi-FQ data sets! (Unless one installs a patch from the patch area.)
  7. 15APR98 COMB handles noise images as inputs and allows a variety of new control options.
  8. 15APR98 has a verb for displaying symbols on the TV at specified celestial coordinates and a verb for centering the data window on a specified coordinate.
* Use 15APR98 for a current CookBook

[15APR98] Poster and paper for ADASS 1997

I have prepared a summary paper and poster for the ADASS meeting to be held in Sonthoven Germany 14-17 September 1997. Warning, these files are 1 and 3 Mbyte files, respectively.

[15APR98] Changes for the 15APR98 version

15APR98 has now been under development for over nearly two years and the number of changes of interest to users has increased steadily. It has reached the point where these changes need to be broken into categories for easier access. Please remember that a number of the changes should be listed in more than one category but are listed in most cases in only one. The categories include full software details, the CookBook, VLA and VLBA, interferometric imaging, interferometric Calibration, data editing and handling, single-dish spectral-line imaging, single-dish continuum imaging, general imaging, display and general matters, and system matters. These sections discuss my work almost exclusively. Work done by the old AIPS group and the AOC group and released is described in the AipsLetters for the 15JAN96, 15OCT96, 15APR97, and 15OCT97 releases. All code described in these documents is included in 15APR98 although a modest number of things required improvement or omission.

Absolutely all the details

All changes in the 15APR98 version are documented in a file called CHANGE.DOC. Press here to see the full text of this file --- warning it is more than 530000 --> --bytes. To view CHANGE.DOC in the most recent three versions --> --including 31DEC99 with more selectivity, you may use a special search tool. Please be aware that this file represents a method of documenting work in progress and it may not be clear in its descriptions even to the people who made the entries. A summary of the changes in CVX, stripped of the technical details, appears below.

The CookBook

***The AIPS CookBook has had to be modified for 15APR98. It has been modified still further for 15OCT98 and you should access that version now. You may reach the latest individual chapters (as PostScript files) through a version of the Table of Contents here or by the references to updated chapters below. Beware: some of the files are large. Of course, if you want to dispense with all that stuff about astronomy, interferometry, and AIPS, you can go straight to the Additional recipes. There are several new ones.


1. FILLM: Changed to produce weights  =   1/sigma**2 using calibrated
          Tant values produced by the VLA on-line system since about May
          1, 1996.  The new-style weights can be forced with a new bit
          option in CPARM(2) but the calibration of the Tant may still
          not be good enough for this usage.
          Changed CPARM(8) to NCOUNT and made CPARM(8) the interval to
          use for TY tables (default = input data interval).  Corrected
          bug in handling table intervals.
          A van Vleck correction may be made for high S/N data, but only
          for continuum data at present.
          It now tests for data out of time order and makes new FQ
          numbers less often due to more careful tests on the
   print: Changed PRTUV, PRTSD, UVPRT, PRTSD, UVDIF, and UVFND to
          examine and, if needed, scale the weights to get a
          meaningful display. 

2. Up to 50 extension file types are now supported.  Translation of
   headers from the previous limit of 20 is automatic. 
   ***** NB older versions may have problems with headers  ********
   ***** created by 15APR98 because of this.               ********

3. File sizes greater than 2 Gbytes are now allowed.  They can be
   created only on DEC Alpha, SGI, and Solaris 2.6 computers at
   present, but all limitations in    non-system-dependent routines
   have been removed.  The disk I/O    routines had numerous extra
   "lseek" calls inhibited.

4. INDXR can now merge atmospheric delay and clock offset data from MC
   tables when creating a CL table.

5. UVFIX now handles orbiting VLBI as do numerous other tasks.

6. The new tasks M3TAR to read MkIII data in Unix tar archives and TFILE
   to sort and edit AFILEs for M3TAR were submitted from MPI Bonn.

7. The largest visibility record (the product of number of spectral
   channels, number of IFs, and number of polarizations) was doubled to
   16384.  All AIPS tasks should be able to handle this (if slowly).

8. COHER:  determines coherence times in data even for non-zero fringe

Interferometric imaging

1. "3D imaging" - Changed IMAGR to offer the option of re-projecting
   the baselines onto the center of each field.  This makes each field
   tangent to the celestial sphere.  Previously - and with DO3DIM
   false - each field is parallel to the initial tangent point.  The
   re-projection allows distant fields to remain "in focus" over a
   much wider area.  Almost all of 15APR98 AIPS now understands these
   images, handling Clean component models made with or without the
   re-projection.  Thus CALIB, UVSUB, FRING, BPASS, PCAL, etc. can
   handle such models as can VPLOT, CLPLT, and IBLED.  The cost of
   this option has yet to be measured properly but appears tolerable.
   The option is essential for P BAND imaging with even modest

2. The maximum number of fields for imaging was changed from 16 to 64.
   This changed the dimension of adverbs FLDSIZE, RASHIFT, DECSHIFT,
   BCOMP, and NCOMP.  It also forced changes in system I/O structures
   and in the Task-Data intercommunication file (IMAGR, the task used
   to compute these  images, now requires 782 words of adverb
   values!).  IMAGR will read in field parameters from the adverbs and
   also from the optional BOXFILE.  Do a HELP BOXFILE to see how to
   use that file to save problems typing in large numbers of adverbs
   in complex problems.  (The BOXFILE option for field parameters was
   not added to MX or WFCLN - use IMAGR, they are obsolete.)   The
   maximum number of Clean boxes was reduced from 500 to 256 per field
   for IMAGR and WFCLN. 

3. IMAGR was given the ability to restore Clean components to all
   fields in which they occur, not just the field in which they were
   found.  IMAGR was also given a new mode of sequencing the imaging
   and Cleaning that should allow the same direction to be Cleaned
   from two or more fields without the previous instabilities and slow

4. FLATN is a new task to create a single (large) output image by
   re-projecting all fields onto a single coordinate grid.

5. SCMAP is the task used to make images using iterative deconvolution
   and self-calibration steps. It was revised to allow the full
   capability of EDITR to be selected from the self-calibration TV menu.
   SCMAP now compares with DIFMAP for VLB and even VLA imaging.  It has
   acquired interactive options to abort the task, to switch to
   amplitude and phase solutions from phase-only solutions, and to reset
   a wide range of parameters.  When doing amplitude and phase
   solutions, it can apply a time smoothing to the solution amplitudes
   before applying them to the data.  This smoothing is also used to
   interpolate over failed amplitude and phase solutions in the hope
   that they won't fail in the next iteration.

***For a sample of an SCMAP TV screen (in EDITR mode) press here. ***

6. UVSUB now has an option to write out the model evaluated at the
   input sample points instead of the difference or ration of the
   observations and model.

7. IMAGR: The operation which caused it to take a long time to end after
   writing the restored image was replaced by a nearly zero cost
   operation while the data are first read.  The work file may be
   re-used, although the data in it are never re-used.  An ABORT-TASK
   option was added to the interactive TV menu.  

8. VPLOT: The 15APR98 versions of VPLOT, CLPLT, and IBLED compute models
   correctly and support the 3D imaging option.  The 15OCT97 versions have
   an error in the model computation and CLPLT does not read the data

Interferometric Calibration

1. The bandpass tables have been changed to include weights which depend
   on IF and polarization.  BPASS will compute them and the calibration
   application routines (and POSSM) will use them.  Older format
   bandpass tables will continue to function, with the missing weights
   taken from the "interval" column.  The new application routines are
   able to do nearest neighbor and two-point interpolation on the
   bandpass table with weights (DOBAND 2 and 3, resp.) and without
   weights (DOBAND 4 and 5, resp.) as well as using the overall average
   bandpasses.  Dynamic memory is used which means that all tasks will
   use as much or as little memory as needed.  CVEL also works with all
   values of DOBAND to shift observations to a common velocity.

   BPASS: In determining bandpass calibration functions from the data,
          the algorithm was improved to correct data weights to take
          into account low fluxes in the continuum division.  New
          adverbs and print controls were added to summarize closure
          Adverbs BCHAN, ECHAN, and STOKES, which caused errors, were
          dropped from the task.  Bugs affecting re-referencing phases
          were corrected.
          Dynamic memory is now used throughout to allow the program to
          run in the space needed be it large or small.

   BPERR: A new task to read closure error reports from text files
          generated by BPASS and PRTMSG.  Averaged and summed reports
          and plots are generated.

2. BPSMO: A new task which makes a regularly gridded (in time) BP table
          via several different interpolation schemes.  It has an option
          to insure amplitude normalization over a range of channels and
          does all interpolation and normalization in either full vector
          or amplitude-scalar modes.  It can do weighted or un-weighted
          smoothing and offers options affecting the output weights.
          BPSMO may also be used just to fill in blanked (i.e. failed or
          flagged) solutions leaving the others alone.

3. BPLOT: A new task to plot bandpasses as profiles in two dimensions.
          Multiple times for one antenna or multiple antennas for one
          time appear in each plot and multiple plots can be produced.
          Multiple IFs and/or polarizations may appear along the
          horizontal axis.

4. UJOIN: A new task to "join" multiple, overlapped IFs either averaging
          the overlapped channels or differencing them.  With the new,
          better bandpasses, this may become a standard operation to be
          done before UVLSF or UVLIN.

5. CALIB: Added adverbs MINAMPER and MINPHSER and changed the meanings
          of APARM(6) (print control), CPARM(3), and CPARM(4) to allow
          more complete examination of closure errors without too much

6. UVMLN: A new task to apply preliminary calibrations (continuum and,
          especially, bandpass) to a multi-source file, then fit a
          baseline to each record (uv spectrum), and generate flags
          whenever residuals in the baseline-fitting regions exceed
          specified limits.  This will let you remove bad samples,
          and re-determine the calibration with cleaner data.

7. ASCAL: This old task, which ignored IFs > 1, has been deleted.
          Its supporting cast (VSCAL, ASCOR, GNSMO, GNMRG, GAPLT,
	  GNPLT, PRTGA) has also been removed.

Data editing and handling

1. EDITA is a new task that allows you to prepare uv-data flag commands
   interactively from displays of TY (system temperature), SN (gain
   solution), and CL (calibration) tables.  It is similar to SNEDT
   (without the smoothing options), but prepares Flag Commands which can
   then be copied into uv-data FG (flag) tables.  It applies a
   pre-existing FG table to the TY, SN, or CL data as they are read so
   that you do not need to flag those data more than once.  EDITA
   talks in user-friendly units for delay and rate although it uses
   sec and sec/sec internally to match the units of the SN/CL files.

2. EDITR is a new task that allows you to prepare uv-data flag commands
   interactively from displays of the uv data and, optionally, a related
   uv data set (e.g. a residual data set from IMAGR, SCMAP, or UVSUB).
   It is a graphics-based editor like EDITA, SNEDT, and (distantly)
   IBLED.  It allows you to look at up to 10 baselines to the selected
   antenna at the same time and to view and edit upon amplitude and
   phase of the data and of the difference between the data and a
   running vector mean of the data.

3. TV editors: TVFLG, SPFLG, EDITR, EDITA all allow you to enter a
          REASON string for subsequent flag commands.
          Problems with gridding data in IBLED, TVFLG and SPFLG have
          been addressed.

4. UVCOP: can now apply a flag table, deleting data, while doing the

5. DIFUV: A new task to write out the difference of two matching uv
          data sets.  Its main uses will probably be (1) to make a
          difference beam-switched single-dish data file for use in
          examining and perhaps editing the data before imaging and
          (2) to make a uv file of the data model by subtracting the
          residual from the input.

6. FIXWT: This new task was not counting flagged data correctly and
          deleted way too much on output.  Fixed reports and also its
          handling of autocorrelation data.  Corrected bug that
          discarded the last XINC samples, added user control over the
          "scan" break interval, and made it smarter in handling "short"

7. DTSUM: Changed task to handle single-dish data, single-source data,
          and missing tables usefully.

8. SPECR: Changed task to work.  Previously it did not do the right
          things at least when increasing the number of channels except
          for the very first spectrum.  Also made it handle
          autocorrelation data correctly.

9. FXTIM: New task to fix times in uv data sets if a wrong reference
          date was selected (leading to negative times).

10. DBCON: Changed task to apply all corrections to compressed as well
          as uncompressed data.  The two data sets do not have to have
          the same compression state.  Corrected the DOPOS phase
          correction to use frequency at all times and to do it

11. Corrected calibration to use the baseline-dependent cal array only
    when requested rather than filling it laboriously with 1's and 0's
    and then doing complex multiplies.  Worse yet, it caused large
    problems to die if the array was too small (which it is by a factor
    of 30 or so in the worst case) even when it really was not used.

Single-dish spectral-line imaging

1. **** BUGS OF NOTE **** :
        The circular convolving functions of SDGRD were found to have an
        addressing error.  The effect was to move the object one-half
        pixel toward decreasing X and toward increasing Y.
        Corrected December 19, 1996.

        Another bug causing bad values of circular convolving
	functions to be used was found and fixed 6 January 1998.  This
	should 	either have used 0 (nearly the right value anyway) or
	really 	bad values producing obvious effects.

2. OTFUV:  OTFUV translates NRAO 12m "on-the-fly" spectral-line data
           into AIPS format.  An option to interpolate the OFF and
           Gain measurements in time before applying them to the ON
           data was added.  In addition, the ability to read up to 8
           "IFs" at a time (from BIF to EIF but excluding those that
           do not match BIF's frequency center and increment) was
           added.  This option avoids the later need for a sort.
           Lower-case file names are now allowed.

3. OTFIN: A new task to print an index of the contents of a 12m
          "on-the-fly" data file.

4. SDLSF: A new task to average all spectra observed at the same time,
          fit a linear baseline to the average, and then subtract that
          baseline from each spectrum.  This is an attempt to remove the
          "weather" before imaging, but its main effect may be to avoid
          the TRANS-IMLIN-TRANS process used after imaging to remove the
          spectral baseline.  For multi-feed instruments dominated by
          instrumental effects, the option to remove a baseline from
          each spectrum individually has been added.

5. SDVEL: New task to shift single-dish spectra to the correct
          velocity  for the actual time and pointing position.  The
          velocity error in a 2x2 degree field can be as much as 1.2
          km/sec which is significant at mm wavelengths.
   VTEST: New task to help determine how big this effect can be.

6. SDIMG: New name for the previous SDGRD task which is able to make
          very large images from single-dish data.

7. SDGRD: This task converts single-dish data into images, potentially
          having multiple spectral channels.  It was completely
          rewritten to be an OOP task.  It is now limited to images
          small enough to fit one plane into the pseudo AP, but it does
          not require the, potentially, very large scratch file still
          used by SDIMG.  The cpu time may be longer than SDIMG since
          the coordinate projection has to be repeated for each set of
          spectral channels, but the real time is usually less. 

8. WTSUM: This task is used to do weighted averages or sums of images
          using images of the weights.  It has been given the option
          to average a large number of input images in a single
          execution, looping over the image "sequence" number.

9. many:  Numerous tasks were fixed to force the "imaginary part" of
          single-dish visibilities to 0.  This part of the data is used
          to store applied offsets and, hence, is not automatically 0.

Single-dish continuum imaging

1. A package of tasks to handle beam-switched on-the-fly continuum
   imaging from the NRAO 12m is in the process of development:
   OTFBS: A new task to read beam-switched continuum data and make two
          AIPS uv data sets, one for "plus" throws and one for "minus".

2. BSGRD: A new task to make a beam-switched image in standard
          coordinates by imaging the plus and minus throws, rotating
          the two images, correcting them by the standard
          convolutional algorithm, and then regridding into standard
          coordinates.  It combines SDGRD, OGEOM, BSCOR, and BSGEO.

3. BSCOR: A new task to combine images made with plus and minus beam
          switching using the "standard" convolutional algorithm.  The
          results have not been exciting and suggest that a new
          algorithm may be needed.  BSCOR is now coded as a class
          method in the AIPS OOP system.

4. BSGEO: A new task to regrid the output of BSCOR into a standard
          right ascension by declination image.  It is coded in OOP.

5. BSAVG: A new task to average multiple BS images using a weighting in
          the Fourier transform space.

6. BSTST: New task to test and plot one-dimensional beam-switched
          restoration (really frequency switched in 1-D).  Options to
          include various instrumental errors are available.

7. BSFIX: A new task to compute and correct the RA and declination
          offsets in beam-switched data.

8. SDMOD: This task subtracts a model from single-dish data or
          replaces the data with a model.  Models are up to 4
          Gaussians or, now, an image.  Beam-switched data may be
          modeled including instrumental errors such as throw length.

General imaging

1. OGEOM: This new task rotates and re-scales the geometry of an image,
          writing a new image.  It handles blanked pixels properly,
          allowing small blanked regions to be filled in.  Older tasks
          like LGEOM increase the blanked area with each application.
          OHGEO, which does a more complicated re-gridding, was also
          enhanced to give the user more controls.

2. SERCH: This new task uses algorithms developed by Juan Uson to
          convolve the spectra in a data cube with Gaussians of
          various widths and then report those pixels/channels having
          signal/noise exceeding a user selected cutoff.  This is a
          good way to find weak signals in large cubes.  The pixels
          found may be written out in a hyper-cube of S/N.

3. ISPEC: Changed to better output formats and to offer the option of
          plotting flux rather than average brightness.

4. BLSUM: Changed task print level controls, corrected handling of
          units, labels, and even which image's header is used to
          control those matters.

5. XBASL: Changed handling of blanks and internal logic to make it
          friendlier for spectral-line (esp single-dish) users.  Some of
          the changes were made in XPLOT and XGAUS as well.

6. POLCO: Changed the task to do a low S/N solution for the correction
          as well as the previous, higher S/N correction.  This allows
          noise in the corrected image to be estimated properly.

7. COMB:  Changed to allow noise images to be input rather than simple
          constants.  A noise image may be written at the same time as
          the usual product image.  PANG has a new clip level on the
          total polarization; SPIX and OPTD also have new clip level
          parameters.  POLC now uses Jim Condon's method covering the
          full range of S/N.  Most prohibitions were dropped and several
          defaults changed.

8. IMERG: Changed to offer a smooth weighting of the two FFTs within
          UVRANGE as well as the previous step function.

9. IMMOD: Added uniform sphere and infinite exponential disk models and
   UVMOD: changed the meaning of some parameters.

Display and general matters

1. XAS: The TV now has a number of improvements.  They include:
          (a) a new icon
          (b) 4 grey-scale memories rather than 2 to allow for better
          (c) initialization, character generation, vector drawing, and
              area fill are now done by XAS itself to reduce I/O
          (d) XAS maintains the device characteristics common values in
              a device-independent manner. They are reset when a new XAS
              begins and ID files are no longer used.
          (e) XAS maintains the image catalog in a device-independent
              manner which means that it is reset when a new XAS begins
              and it may be used correctly by any computer anywhere.
              IC files are no longer needed.
          (f) Access to XAS is controlled by a new server program
              TVSERV.  Tasks wanting to use XAS on computer Host ask the
              TVSERV on Host for permission to use it.  Previously,
              remote requests would hang until the TV became available;
              now they hang until TVSERV is available (which will be
              milliseconds at most).
        Access over networks is improved by corrections that remove
        the assumption that $AIPS_ROOT is the same at all sites.  It
        is now entirely feasible to run at a very remote site while
        having XAS et al. on your desk.

2. XAS and other servers: All servers will now work with Unix as well
          as Internet sockets.  The servers have all been given
          interrupt handling and close-down procedures.  Unix sockets
          should be faster - as soon as we get them fully implemented
          - when the compute and display servers are the same.  they
          should allow us to support multiple display servers on a
          single host (each with its own X terminal or other display
          output device).

3. SNPLT: Adverb FACTOR was added to allow control of the size of the
          plot symbols.  They were too large under some circumstances.
          A bug preventing the plotting of error bars was fixed.

4. PRTAB: Adverbs NCOUNT, BDROP, EDROP, and BOX were added to allow
          control of which elements in arrays are printed (1-NCOUNT and
          BDROP-EDROP) and of which columns are printed in what order
          (all or as listed in BOX).  Handling of flagged rows was

5. TVMOVIE: Button D may now terminate the movie loading in case you
          have gotten the adverbs wrong (which I always seem to do).

6. TVCPS: Changed task to use the zoom and scroll parameters so that it
          is much more WYSIWYG.

7. HELP:  Changed this verb (and EXPLAIN) to use the TASK adverb when
          there is no immediate argument.

8. PRINTER: New verb developed by Pat Murphy to allow interactive
          changes to the output print device.

9. PRTSD and UVPRT: Changed these two tasks to use BCOUNT as an offset
          into the file rather than reading the first BCOUNT records
          before printing.  This makes the effect of BCOUNT
          independent of the other adverbs and hence predictable and
          very much faster.

10. KNTR: Added option to have the step wedge over the full range of
          image intensity rather than just PIXRANGE.

11. COSTAR: New verb to plot a symbol at a coordinate on the TV.
    COWINDOW: New verb to set BLC and TRC to be centered on a
    COTVLOD: New procedure to load the TV with a window centered on a

System matters

1. Added a host speed parameter so that various delays may be made
   shorter on faster computers.  Examples are how often AIPS checks
   to see if a task is running when DOWAIT is true. 

2. Added a translation of $HOST to the internals of AIPS.  This name
   is then used on printouts, accounting, etc. rather than the SYSNAM
   which is "UNREGISTERED!!!!!" on all machines that are not
   registered.  This fix keeps two hosts from destroying each others
   scratch files on shared data areas. 

3. Esthetic and real problems with the year 2000 have been addressed.
   15APR98 already reads the proposed new FITS date format and is poised
   to write it when allowed to do so.  Both the old and new date
   formats are handled internally and transparently.

4. 15APR98 now supports a Solaris-like "operating system" called SUL to
   allow Ultra-specific and non-specific Solaris versions to co-exist.

5. The number of tape drives is determined from a local environment
   variable set in the AIPS startup rather than depending on the
   contents of the hand-maintained SP file.

Eric W. Greisen