cal-persia.el disagrees with Iranian calendar in A.D. 2025

[Ed Reingold]

> On Tue, 2005-04-05 at 15:02 -0700, Paul Eggert wrote:
> > This suggests that cal-persia.el could be changed as well, as its
> > practical use is (I think) for predicting dates in Iran.  I'm hesitant
> > to propose a change myself, though, as I'm not an expert in either the
> > calendar or the code.
> 
> Ed could probably help with that... I don't know any LISP, and every
> useful thing I know about computing astronomical calendars comes from
> his book.

As I have said before, the mechanisms needed to do the Persian astronomical 
calendar are not in the existing Emacs code; the algorithms in my Calendrical 
Calculations will never be released under the GNU license, so somebody would 
have to come up with entirely new algorithms and implement them in Emacs-Lisp.

As it stands, the arithmetical Persian calendar is an excellent approximation 
to the astronomical version--a much better approximation than the GNU Emacs 
arithmetic approximation to the Islamic calendar is to the true observational 
Islamic calendar.

I don't see any reasonable changes to cal-persia.el as being needed.  The
documentation could be modified to state that the calendar as implemented is 
a close approximation to the astronomical version.  I leave that up to others.