Julian-Gregorian Date Calculator

[Peter Meyer-3]

Dear CALNDR-L members,

Software hot off the press.
The user manual is at http://www.hermetic.ch/jgdc/jgdc.htm
To get the trial version follow the download link
at the bottom of the page.

The trial version is fully-functional as regards
date conversion.  There's an arithmetical function
for which the software must be activated via a key.
Any member of CALNDR-L may request a complimentary
user license (which gets you a key) by emailing a
request to me and stating that they are a member
of this list.

I've tested this software and AFAIK it is bug-free,
but merciless treatment at the hands of list members
might turn up something.  Bug reports should be
sent to bugs@....  Comments welcome.

BTW, as noted on that web page (and this was found
by use of the software):

The next date which is on the same day of the week in both
calendars (Julian and Gregorian) is 2100-03-01, which is a Monday
in both. This situation will continue until 2200-02-28, which is
a Friday in both calendars. 2200-02-29 JC is a Saturday,
but there is no 2200-02-29 CE. The date following 2200-02-28 CE
is 2200-03-01 CE, which is a Saturday, whereas 2200-03-01 JC is
a Sunday.

Perhaps Karl can provide a concepual/mathematical proof
re 2100-03-01 and 2200-02-28.

Regards,
Peter Meyer

[Karl Palmen]

Dear Peter and Calendar People

I reply below.

-----Original Message-----
From: East Carolina University Calendar discussion List
[mailto:CALNDR-L@...] On Behalf Of Peter Meyer
Sent: 13 October 2009 15:44
To: CALNDR-L@...
Subject: Julian-Gregorian Date Calculator

Dear CALNDR-L members,

Software hot off the press.
The user manual is at http://www.hermetic.ch/jgdc/jgdc.htm 
To get the trial version follow the download link
at the bottom of the page.

The trial version is fully-functional as regards
date conversion.  There's an arithmetical function
for which the software must be activated via a key.
Any member of CALNDR-L may request a complimentary
user license (which gets you a key) by emailing a
request to me and stating that they are a member
of this list.

I've tested this software and AFAIK it is bug-free,
but merciless treatment at the hands of list members
might turn up something.  Bug reports should be
sent to bugs@....  Comments welcome.

BTW, as noted on that web page (and this was found
by use of the software):

The next date which is on the same day of the week in both
calendars (Julian and Gregorian) is 2100-03-01, which is a Monday
in both. This situation will continue until 2200-02-28, which is
a Friday in both calendars. 2200-02-29 JC is a Saturday,
but there is no 2200-02-29 CE. The date following 2200-02-28 CE
is 2200-03-01 CE, which is a Saturday, whereas 2200-03-01 JC is
a Sunday.

Perhaps Karl can provide a concepual/mathematical proof
re 2100-03-01 and 2200-02-28.

KARL SAYS: Firstly the property that a particular date is so many days
later in the Julian calendar compared to the Gregorian calendar is a
property of DATES and not of DAYS. It is therefore a dodgy basis for a
calendar conversion algorithm. I hope Peter does not use it as a basis
for his conversion algorithm. Else, I'd suggest checking days such as
March 10, 2100 CE or February 20, 2100 JC.

For DATES that are the same day of week in both calendars, just count
number of Gregorian dropped leap days from one such known period and we
get
2100-03-01 to 2200-02-28 (14 DAY difference)
2200, 2300, 2500, 2600, 2700, 2900, 3000
3000-03-01 to 3100-02-28 (21 DAY difference)
etc...
This can also be worked backwards in the proleptic calendars.
A 2800-year cycle with three such periods emerges with starting and
ending years thus:
200-300, 1100-1300, 2100-2200,
3000-3100, 3900-4100, 4900-5000,
5800-5900, 6700-6900, 7700-7800,
... .


I also ask what does this software offer that is not available at
websites such as
http://emr.cs.iit.edu/home/reingold/calendar-book/Calendrica.html
http://www.ortelius.de/kalender/form_en2.php 
http://www.fourmilab.ch/documents/calendar/
http://isotropic.org//date/
http://the-light.com/cal/converter/  ?


Karl

10(13(26

--
Scanned by iCritical.

[Peter Meyer-3]

KARL SAID: Firstly the property that a particular date is so many days
later in the Julian calendar compared to the Gregorian calendar is a
property of DATES and not of DAYS.

I REPLY:  Whoever said it wasn't?  Actually the property I mentioned
is a property of instances of date notation, e.g. '2100-03-01', not
of dates or of days.

KARL CONTINUED: It is therefore a dodgy basis for a calendar conversion
algorithm. I hope Peter does not use it as a basis for his
conversion algorithm.

I REPLY: Of course not.  I'm surprised that the thought
should even have occured to you.

KARL SAID: I also ask what does this software offer that is
not available at websites such as ...

I REPLY: You don't have to be online to use it.

If it doesn't appeal to you then stay with what you like.

And as Terence McKenna used to say:
"There's always room for one more good Italian restaurant."

Regards,
Peter Meyer
Hermetic Systems, http://www.hermetic.ch/

[Karl Palmen]

Dear Peter and Calendar People

-----Original Message-----
From: East Carolina University Calendar discussion List
[mailto:CALNDR-L@...] On Behalf Of Peter Meyer
Sent: 15 October 2009 10:53
To: CALNDR-L@...
Subject: Re: Julian-Gregorian Date Calculator

>KARL SAID: Firstly the property that a particular date is so many days
later in the Julian calendar compared to the Gregorian calendar is a
property of DATES and not of DAYS.

>I REPLY:  Whoever said it wasn't?  Actually the property I mentioned
is a property of instances of date notation, e.g. '2100-03-01', not
of dates or of days.

KARL SAYS: It's an easy mistake to make.

>KARL CONTINUED: It is therefore a dodgy basis for a calendar conversion

algorithm. I hope Peter does not use it as a basis for his
conversion algorithm.

>I REPLY: Of course not.  I'm surprised that the thought
should even have occured to you.

>KARL SAID: I also ask what does this software offer that is
not available at websites such as ...

>I REPLY: You don't have to be online to use it.

KARL SAYS: I thought you'd say that its capable of putting the results
into a file, which could be printed.
If you seriously want money for the software, I suggest you make such
points well known and perhaps enhance such functionality in later
versions.

If it doesn't appeal to you then stay with what you like.

And as Terence McKenna used to say:
"There's always room for one more good Italian restaurant."

KARL SAYS: But if one restaurant gives away its food free, ....

Karl

10(13(27

--
Scanned by iCritical.

[Peter Meyer-3]

Dear Karl and Calendar People,

KARL SAID: I also ask what does this software offer that is
not available at websites such as ...

I REPLIED: You don't have to be online to use it.

KARL REPLIED: I thought you'd say that its capable of putting
the results into a file, which could be printed. If you seriously
want money for the software, I suggest you make such points
well known and perhaps enhance such functionality in later versions.

I NOW SAY:  

JGDC does not allow directly putting the results into a file,
but in the full (non-trial) version a button appears which
allows you copy the results to the clipboard, from where
they can be pasted into Notepad or similar, from which they
can be printed.

Suggestions for enhancements are welcome.

Note, however, that no purchase of a user license is required
for the complete functionality of the Julian-Gregorian date conversion.
Purchase (at a mere $9.95) provides (in addition to the clipboard-copy
mentioned above) access to the arithmetic function (adding/substracting
days, etc.).

I never claimed that JGDC handled dates in any calendars beyond
the Julian and the Gregorian, so to compare it to online
calculators that handle dates in umpteen calendars is inapposite.

As noted above, KARL SAID: what does this software offer
that is not available at websites such as ...

I REPLY:
JGDC allows user-preferred year designators (AD,BC,CE,BCE).
It also allows user-preferred date input format (popular
or astronomical year numbering).
It also allows identification of calendar by combination of
month,day,year with a day-of-week.
It also allows addition/subtraction of days,weeks,months,years
to a given input date.

Which of Karl's cited online calculators have any of these?
Do any of them have all?

I QUOTED Terence McKenna:

"There's always room for one more good Italian restaurant."

KARL SAID: But if one restaurant gives away its food free, ....

I REPLY: Proprietors of good Italian restaurants always like
to make a living from their work, besides providing good food
to their customers.  Makers of online calculators don't try to
make a living from their efforts because they usually have
well-paying jobs (such as professorships at universities).

Actually, since Karl raised the point, Hermetic Systems
does give away some software for free:
Five Cellular Automata:
http://www.hermetic.ch/pca/pca.htm
Index Files Search Words Lite:
http://www.hermetic.ch/ifswl/ifswl.htm

Regards,
Peter Meyer