March 2005 Visiting Committee Report on AIPS The 31DEC04 version of AIPS was developed through 2004 and then frozen in late December. It was available for download (and update via the "midnight job" or MNJ) during development and the frozen version may now be downloaded. The new test version, 31DEC05, was started in December 2004 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 797 sites in 2004 of which 231 appear to have run the MNJ at least occasionally. The frozen 31DEC03 version was downloaded by 196 sites and the 31DEC04 version, while under development, was downloaded by 808 sites. A total of 1276 unique IP addresses downloaded a copy of AIPS and/or accessed the cvs site. At this writing (15 February), the frozen 31DEC04 version has been downloaded by 69 sites and the development 31DEC05 version has been downloaded by 190 sites. The total number of IP addresses is already 364. 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, the IBM compiler is moderately expensive. Therefore, we have made available a binary distribution of AIPS. This binary form is available both for the frozen 31DEC04 release and the development 31DEC05 version, including periodic updates (daily are possible) via the MNJ. For completeness, binary installations are available for MacIntosh OS/X (IBM compiler), SUN Solaris (SUNWspro compiler), and Linux (GNU g77 2.95.3 compiler). The Intel compiler for Linux has recently been tested. It failed to work with aggressive optimization and, with less optimization, its performance was only slightly better than that of the GNU compiler. Steps are being taken to support greater use of pipeline and other procedures in AIPS. A large task FLAGR was written to use the internal statistics in a data set to flag that data set. The new task FINDR was written to determine some of the same statistics, returning values to the AIPS user. Studies are now underway to determine how these tasks may be used in AIPS' VLA and VLBA data reduction pipelines, particularly in flagging calibration sources. Models for the primary flux calibration sources are now provided with AIPS. There are four sources, 3C48, 3C138, 3C147, and 3C286, at the three highest VLA frequency bands, K, Q, and U. These models were provided by Claire Chandler. X-band (3.6-cm) models for 3C48 and 3C286 and a C-band (6-cm) model for 3C48 have been provided so far by Amy Mioduszewski. We expect, in the long run, to provide models for all four sources at all VLA frequencies. The pipeline procedures for the VLA are being revised to use these models. The verb CALDIR to list available models and the task CALRD to read in models were added to AIPS. The calibration and bandpass tasks, CALIB and BPASS, were revised to offer "robust" gain solution methods. Such methods progressively refine solutions by ignoring significantly discrepant data at each iteration. This change in the fitting routines provides data to allow CALIB to flag visibilities with significant closure error. BPASS was changed to handle channel-dependent flagging correctly. A new task, ATMCA, was written to refine the calibration during phase-referencing observations through the use of additional calibration sources. The direction-dependency of phase error is fit from the multiple calibration observations and used to refine the gain solution on the target source. AIPS Memos on ATMCA and the earlier DELZN astrometric-level calibration tasks were released. Note that both these tasks require observations to be scheduled to provide the additional calibration information required to model the atmospheric direction dependency of phase. The AIPS CookBook was kept up to date as always. In addition, it was developed so that, in addition to the usual PostScript version, both html and pdf versions exist. The latter provide full cross-reference capability including using the web browser to examine cross-linked help files. This XHELP facility was corrected and greatly enhanced during 2004. In the past, when the Midnight Job detected changes in certain system-like files, all the AIPS Managers were alerted and instructed to perform a variety of manual operations. The MNJ procedures were changed to do almost all of these automatically, greatly simplifying the Managers' job. The installation from CDrom was tested and corrected. It is actually pretty slick. The new task FIXBX converts Clean windows from one set of cell size and facet locations to another. New tasks to renumber frequency IDs and sources were written. New verbs to draw Clean boxes on the TV, to return random numbers, and to provide direct access to the operating system were added. The last has interesting implications for pipelines and can even run an AIPS beneath the current one. Task upgrades included a number of changes to IMAGR to enable the Steer-Dewdney-Ito Clean algorithm to be used efficiently. The complex Clean task and procedure (CXCLN and CXPOLN) were corrected. On-the-fly imaging is still done at the 12-m telescope, formerly operated by the NRAO, and AIPS can now handle the new, changed data format as well as the older one. All plot tasks and verbs that used the Tektronix-emulation window now offer a TV-window equivalent. The VLA data filling task FILLM was changed in numerous small ways to handle various error conditions, to deal with multiple data sets from the archive, and to precess coordinates in a manner consistent with the rest of AIPS.