[net.math] Jewish to Gregorian

iles@hplabs.UUCP (01/09/85)

Converting the Jewish calendar to any other calendar is quite trivial, actually.

Recall that the Jewish calendar is mereley a sequential ordering of months,
identical to the Gregorian calendar, only instead of a leap day added during
a long calendar year, there is a leap month.

Therefore, to calculate any give Jewish holiday in, say, 1995, one only must
know what day of the Jewish calendar it is today, and what year in the leap
cycle.  It is then rather easy to find the total number of days until the
holiday occurs again, and then to plug this number of days into a gregorian
calendar.

If there is sufficient interest, I will write such a mess sometime during the
next semester.  What language would you people like it in, if requested?

The program, if I supplied it, would merely ask for the Jewish date, or 
holiday by common name, and either the Jewish year, or the Gregorian year.
Fair enough?

Daniel Lieman 

"yeah, I'm on Doug's account, but that's okay, cause I do work here 1/2 time."

nachum@uiucdcs.UUCP (01/10/85)

Converting the Jewish calendar to another is not quite that simple,
as the solutions posted here show.
The reason is that there are 2 variable months per year,
that can be either 29 or 30 days.
And that depends on which time of which day of the week
the beginning of the year (12 or 13 months long) falls.

nachum@uiucdcs.UUCP (01/13/85)

As Maimonides wrote, "these calculations [of the Jewish calendar],
even schoolchildren can master in three-four days."

iles@hplabs.UUCP (01/14/85)

Authors Note:  Please change the word trivial in the previous note to
               something less offensive to those who have written
               mail about how non-trivial it is.

But the diffference between a simple formulae and a simple program is
quite great.  A simple program can be a straightforward application
of 100 various rules, which would never qualify as a simple function.

Certainly it is nowhere near as "simple" as the calculation of Easter,
but a Jewish/Gregorian conversion is not impossible.  It would not
be cheap on CPU time to say, request Lag B'Omer in 6225, but to go
ahead and crank out the Jewish Holidays for the next few years
sequentially is not expensive.  I presumed that was the intent of the
message.  I did not propose to solve an academic problem, rather a
pratical one.

If someone wants a program that will schedule for the next few years,
then I stand by my offer.

If someone wants a program which will arbitrarily calculate any holiday
of any year by a simple calculation, that I cannot provide.

I apologize to those I have offended by shrugging at the problem,

-DL

"He who thinks himself the wise man is, alas, but the fool amonst us."
 -with apologies to W.S.
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