Changes for SOFA Issue: 2020-07-21

 Summary of Changes

The changes fall into the following categories:

• Correction of a sign in routine P06E.
• Correction in the ANSI C macro function dnint in the include file sofam.h, to improve rounding.
• Improvements in precision and rounding (see items 2 and 3 below).
• Miscellaneous typographical corrections and improvements to various other documents.

 Changes to the SOFA FORTRAN Library

• iau_P06E — Correction. The series are taken from Table 1 of Hilton, J. et al., 2006, Celest. Mech. Dyn. Astron. 94, 351., and it has been discovered that the one for general precession, p_A, had the wrong sign for the t^5 coefficient. The error in the paper has been corrected in the SOFA code. The correct value is -0.0000000383 arcsec. (Even after five centuries the error would be lower than 250 microarcsec.)
• iau_PB06 — Improvements in the method of decomposing the rotation matrix by ensuring that angles near zero are preferred.
• Improvements by ensuring precision is not lost when splitting date and time.
  • iau_JD2CAL
  • iau_JDCALF
• iau_DAT — Release year updated.
• t_sofa_f.for — Updated due to the correction in iau_P06E.
• Minor corrections/improvements to the documentation of the following routines
  • iau_FK524
  • iau_FW2M
  • iau_GMST82
  • iau_TRXP
  • iau_XYS00A

 Changes to the SOFA ANSI C Library

• iauP06e — Correction. Correction. The series are taken from Table 1 of Hilton, J. et al., 2006, Celest. Mech. Dyn. Astron. 94, 351., and it has been discovered that the one for general precession, p_A, had the wrong sign for the t^5 coefficient. The error in the paper has been corrected in the SOFA code. The correct value is -0.0000000383 arcsec. (Even after five centuries the error would be lower than 250 microarcsec.)
• sofam.h — Correction to dnint(A). The existing dnint macro could incorrectly round numbers just over -0.5 and just under +0.5 due to the loss of precision when calculating ceil(A-0.5) or floor(A+0.5). A preliminary test for |A|<0.5 has been added to ensure that such numbers always round to zero. As none of the SOFA C functions depend critically on perfect rounding, the change is unlikely to affect user applications noticeably, though critical round-trip tests may see an improvement.
• iauPb06 — Improvements in the method of decomposing the rotation matrix by ensuring that angles near zero are preferred.
• Improvements by ensuring precision is not lost when splitting date and time.
  • iauJd2cal
  • iauJdcalf
• iauDat — Release year updated.
• t_sofa_f.for — Updated due to the correction in iauP06e.
• Minor corrections/improvements to the documentation of the following routines
  • iauA2af
  • iauA2tf
  • iauD2tf
  • iauFk524
  • iauFw2m
  • iauGmst82
  • iauTrxp
  • iauXys00a

The SOFA Board thanks all those who have reported the various issues that go to ensuring the libraries and documentation are kept up-to-date and relevant.

SOFA Release 16: This changes file was updated on 2020 July 21.