March 2004 Visiting Committee Report on AIPS The 31DEC03 version of AIPS was developed through 2003 and then frozen in late December. It was available for download (and update via the "midnight job") during development and the frozen version may now be downloaded. The new test version, 31DEC04, was started in December 2003 and is available for download and update. We have developed tools to count downloads of full AIPS versions and to count access to the main "cvs" site. The latter reflects both initial installation and updating of the development version; frozen versions do not generate cvs accesses. Counting each unique IP address as a "site", there were cvs contacts from 551 sites in 2003 and from 251 sites so far in 2004. We started counting downloads in May 2003. Since then, the frozen 31DEC02 version was downloaded by 88 sites and the 31DEC03 version, while under development, was downloaded by 416 sites. At this writing, the frozen 31DEC03 version has been downloaded by 81 sites and the development 31DEC04 version has been downloaded by 217 sites. We have found that the GNU 3.2.2 version of the compilers, which is shipped with RedHat 9, works reasonably well so that AIPS users can get out of the compiler-installation game, at least with Linux We have found that the Fortran compiler developed by IBM for MacIntosh systems generates code that is 50% faster than that produced by the GNU compilers. Unfortunately, IBM has begun to charge for their compiler. We are looking into ways in which NRAO might provide binaries, generated by this compiler, rather than forcing all MacIntosh users to spend the non-trivial cost for the IBM compiler. The installation script continues to be improved as various minor problems are encountered. The largest change was to allow a machine to be called a "laptop" in order to avoid problems caused by the machine's name apparently changing every time it is plugged into a LAN. The code was revised to accept read-only file systems, thereby allowing DVD media written on +RW drives to be used on read-only drives. Steps are being taken to support greater use of pipeline and other procedures in AIPS. The set of procedures to reduce VLA data in a pipeline was introduced. A new task, RLDIF, was written to determine the right minus left phase difference and return it to procedures to allow the polarization calibration to be completed. Other tasks such as model-fitting tasks were modified to return their results for use in procedures or verbs. The separation between input and output adverbs was clarified; INPUTS no longer displays output-only adverbs, OUTPUTS is required. The calibration and fringe-fitting tasks were given the ability to determine solutions in time intervals that overlap. This should resolve lobe ambiguities while giving adequate signal-to-noise. The main flux calibration task now uses the source "V polarization" to do different calibration for the RR and LL polarizations. This will be used for WSRT data primarily, where "V" is actually Stokes Q and "RR/LL" are actually XX/YY. The tasks which smooth solution tables and interpolate them to calibration tables were generalized with greater user control added and a few bugs removed. A new task, DELZN, was written to determine residual zenith delays and clock errors from observations of phase calibrators over multiple angles in the sky. This task can apply the corrections to the calibration table. Another new task, DFCOR, can apply these corrections in a differential fashion for rapid phase-referencing observations. The VLBI calibration task APCAL was improved substantially in its ability to estimate and correct for atmospheric opacity, using the weather data which now comes with all VLBA data sets. VLBA observations using the VLA as one of the stations are now supplied with a full set of calibration and weather information for the VLA station. The use of color in AIPS plots was enhanced even more. Plot tasks may now draw lines in any color they choose. The tasks PCNTR and KNTR were given options to let the spectral channel control the color of contour drawings and to let the position angle control the color of polarization vectors. The latter allows the viewer to see the position angle even when the vectors are too short for accurate estimation of their directions. Other tasks now use full color to separate symbols plotted for different spectral channels, IFs, and/or polarizations. A few new verbs were written to assist in plotting on the TV, using TV colors in plot files, and resetting coordinates. Three new tasks were written to allow users to remove source name and qualifier information from a data set and to discard the cross-hand polarizations. Two new tasks were also added to assist array configuration studies, one to estimate loss due to shadowing and the other to convert formats primarily for site masks.