ABSTRACT  for  DAYDATE  etc.                        as of  18 March 1996

by   Prof. W. Kahan                              wkahan@cs.berkeley.edu
     Mathematics Dept. #3840,   and                      (510) 642-5638
     Elect. Eng. & Computer Science Dept. #1776
     University of California
     Berkeley   CA  94720-1776




" Computing  Days between Dates,  the Day of the Week,  etc."

The year  2000  will be a leap year but  2100  will not;  that is how
the  Gregorian  calendar has been working since  1582 .  Will  4000  be
a leap year?  Why do  Sept., Apr., June  and  Nov.  have  30  days and
the rest  31  except for  Feb.?  These questions are discussed,  and to
save programmers the bother of looking up their answers in tables a few
formulas are supplied.  These have been embedded in  MATLAB  functions
ETIME,  J2YMD  and  YMD2J  for handling,  respectively,  elapsed time,
days between dates,  and the  Day of the Week.  Incidentally,  YMD2J
descends from an ancient self-checking progam used in  H-P  financial
calculators since  1976;  despite roundoff,  it assesses the validity
of its output and input by running an inverse program  J2YMD .  Alas,
the explanatioin of all this stuff,  the file  daydate.txt,  displays
properly as an  ASCII  file only on an  IBM PC  or compatible.

Text files:       http://http.cs.berkeley.edu/~wkahan/daydate/ ...