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/ ...