2001 April 1-June 30 AIPS Quarterly Report
                                
AIPS
     Versions - The 31DEC00 version of AIPS, both in its frozen form and in its previous incarnation
as 31DEC99, has now been distributed 581 times, all but 13 of them by ftp.  This includes 174 copies of
the frozen 31DEC00 release, 58 of which occurred in the second quarter of 2001.  Our counts include
those who grab copies on multiple occasions from the ftp site, since we do not have an accurate count of
repeat downloads.  Almost all of the distributions have been of source code only.  The 31DEC01 version,
updated daily, has now been distributed 266 times.  Of the 40 sites that have registered their use of
31DEC01, 2/3 report that Linux is their primary architecture and 1/3 Solaris.
     Personnel - Pat Murphy, because of the press of his other duties, has asked to be relieved of all
official duties in the AIPS group.  He has been a valuable member of the Group for over 10 years and he
will be missed.  Like Bill Cotton before him, he has volunteered to advise the remaining group privately as
needed.  Additional assistance with operating system matters will now be provided by the very capable
members of the Computer Division at the Array Operations Center in Socorro.
     Key Developments - 
               1.   Version 2.4.2 of the Linux kernel has been included in the RedHat 7.0 release of Linux,
          which contains numerous system improvements.  Unfortunately, this and other Linux
          releases include the unofficial "GNU compilers version 2.96," not supported by the GNU
          compiler group.  The AIPS group has recommended installation of the older GNU
          compiler suite version 2.95 along with RedHat release 7.1.
               2.   Wide-field imaging has been improved considerably, largely to facilitate VLA
          observations at 74 MHz.  Considerable improvement has been made in the routines
          selecting and imaging multiple fields ("facets"), and in deciding which fields to clean.
               3.   Improvement of the VLBI data-reduction procedures has continued.  New
          documentation is found in Appendix C of the AIPS Cookbook, "A Step-by-Step Guide to
          VLBA Data Calibration in AIPS," and in AIPS Memo No. 105, "AIPS Procedures for
          Initial VLBA Data Reduction, Version 2.0," dated April 26, 2001. 
               4.   Several changes were made in FILLM to remove lingering bugs that caused problems
          with some aspects of data selection, or when frequencies or antennas changed during an
          observing run.  A user option was added to permit the calculation of Channel 0 in AIPS
          rather than using the (suspect) Channel 0 computed by the VLA on-line system..
               5.   BPASS and CPASS were fixed to correctly incorporate source models in the
          normalization of the bandpass shapes.
               6.   Three new editing tasks were added.  SNFLG, based on code submitted by Lincoln
          Greenhill and Mark Reid of CfA, flags data based on phase changes in SN or CL tables. 
          DEFLG flags based on coherence losses, computed by comparing vector and scalar
          averages in a sliding window.  VPFLG flags data in all polarizations if any individual
          polarization is flagged (important for proper polarization imaging).
               7.   The Brandeis VLBI group contributed AIPS Memo No. 106, "Making Movies from
          Radio Astronomical Images with AIPS," by Cheung et al., dated June 6, 2001.
     Goals for Q3 2001 -
               1.   Continuing maintenance and user support.
               2.   Test capabilities of FRING vs. KRING for fringe-fitting under various conditions.
               3.   Continued low-level code development in support of NRAO instruments.
               4.   Move primary copy of AIPS to Socorro, and revise midnight job procedures.