From: jnshapi@argo.ecte.uswc.uswest.com (Jim Shapiro)
Subject: Re: Friday 13th, try it yourself (was Language Wars..)
Date: 1996/09/26
Date: 1996-09-26T00:00:00+00:00 [thread overview]
Message-ID: <52enm9$d53@aeon.ecte.uswc.uswest.com> (raw)
In-Reply-To: 52b2ks$jcb@internet.csl.co.uk
Barrie Walker (bwalker@csl.co.uk) wrote:
: In article <R.521pfp$kec@ns.ccsn.edu>, mose@ns.ccsn.edu says...
: >
: >Reposting article removed by rogue canceller.
: >
: >Clinton Pierce <cpierce1@ford.com> writes:
: >
: >>See for yourself if the "Friday the 13th" thing is just a UL. If you trust
: >>UNIX's 'cal' program, and that it does the Right Thing with Leap Years, the
: >>Gregorian/Julian switch etc..etc... This Perl script will show you the
: Truth:
: >
: > I decided to write a script of my own for Solaris 2.4 and perl
: >5.003 which calls cal for 1066 to 1996 and rips out the Fridays. The
: >following is the number of times a particular day of the month falls
: >on a Friday. The results are pretty evenly distributed, i.e. it is an
: >Urban Legend.
: I think you have caught hold of the wrong end of the stick.
: The observation doesn't claim
: 1 that 13ths have a monopoly on Fridays -
: 6ths, 20ths and 27ths fall on just as many Fridays.
: 2 that the uneven distribution is restricted to Fridays -
: months are more likely to begin (1sts) on Sundays.
: 3 to work with anything but the current inplementation
: of the Gregorian calendar.
[well written Perl code deleted]
I ran your program and got the same results, then I realized that this whole
argument is silly. Suppose, for the sake of argument and with no loss in
in generality, we look at the day of the week the first of each month falls
on. If January starts on say a Monday, the days for the remaining 11 months
depend only on the number of days in each month. If all the months were 28
days (or any number that is congruent to 0 (mod 7) then _all_ the firsts would
be on Monday! Given the odd ball number of days in each month (a number which
even changes with the year, for some years) the firsts of each month will
be divided among the days of the week in some _deterministic_ fashion. Over
a 400 year interval it does not come out exactly evenly distributed. That is
all there is to it. Why does anyone think that firsts or thirteenths or any
day should be equally likely to be on any one weekday over any other in the
first place?
I guess it is a little counterintuitive, sort of like the famous birthday
problem, one which I will not introduce to keep the thread length in check.
: --
: Barrie
: Edinburgh, Scotland http://www.csl.co.uk
--
Hope this helps,
Jim Shapiro
next prev parent reply other threads:[~1996-09-26 0:00 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
1996-09-13 0:00 language wars (results 13 September) last posting Roy Gardiner
1996-09-13 0:00 ` William Clodius
1996-09-13 0:00 ` Peter Seebach
1996-09-21 0:00 ` Robert Dewar
1996-09-21 0:00 ` Robert Dewar
1996-09-16 0:00 ` Robert Fahey
1996-09-18 0:00 ` James Giles
1996-09-18 0:00 ` Luke Chao
1996-09-18 0:00 ` Andrew Gierth
1996-09-18 0:00 ` Norman H. Cohen
1996-09-18 0:00 ` James Giles
1996-09-19 0:00 ` Andrew Gierth
1996-09-19 0:00 ` Norman H. Cohen
1996-09-19 0:00 ` Daniel J. Long
1996-09-21 0:00 ` Ken Pizzini
1996-09-21 0:00 ` Ken Pizzini
1996-09-24 0:00 ` Art Schwarz
1996-09-26 0:00 ` Ken Pizzini
1996-09-29 0:00 ` Paul Gilmartin
1996-09-26 0:00 ` Matthew D. Healy
1996-09-29 0:00 ` Randy MacDonald
1996-10-03 0:00 ` galina.kasminskaya
1996-10-03 0:00 ` Dave Tholen
1996-09-20 0:00 ` Friday 13th, try it yourself (was Language Wars..) Clinton Pierce
1996-09-21 0:00 ` Russell Mosemann
1996-09-21 0:00 ` Russell Mosemann
1996-09-25 0:00 ` Barrie Walker
1996-09-26 0:00 ` Jim Shapiro [this message]
1996-09-25 0:00 ` Ken Pizzini
1996-09-25 0:00 ` Results of my test: Re: Friday 13th, try it yourself Lee Crites
1996-09-25 0:00 ` William Clodius
1996-09-27 0:00 ` Dik T. Winter
[not found] ` <52qpqt$1b3l@ilx018.iil.intel.com>
1996-10-02 0:00 ` Dik T. Winter
1996-10-02 0:00 ` Ken Pizzini
1996-09-26 0:00 ` Dr John Stockton
1996-09-26 0:00 ` Lee Crites
1996-09-26 0:00 ` John Winters
1996-09-26 0:00 ` Daan Sandee
1996-09-26 0:00 ` Jeff Drummond
1996-09-30 0:00 ` Ray Dunn
1996-09-26 0:00 ` Adam Beneschan
1996-09-27 0:00 ` Glen Clark
1996-09-27 0:00 ` CHI Research, Inc.
1996-09-27 0:00 ` Lee Crites
1996-09-28 0:00 ` John Winters
1996-09-30 0:00 ` Adam Beneschan
1996-10-01 0:00 ` Mike McCarty
1996-09-26 0:00 ` Dr John Stockton
[not found] ` <199609302101.JAA04610@kauri.vuw.ac.nz>
1996-09-30 0:00 ` Lee Crites
1996-09-23 0:00 ` Friday 13th, try it yourself (was Language Wars..) Matthew D. Healy
1996-09-23 0:00 ` Dik T. Winter
1996-09-25 0:00 ` Paul Gilmartin
1996-09-20 0:00 ` language wars (results 13 September) last posting John Girash
1996-09-20 0:00 ` John Girash
1996-09-22 0:00 ` Friday 13th, try it yourself (was Language Wars..) Dr John Stockton
1996-09-23 0:00 ` Dr John Stockton
1996-09-23 0:00 ` Randy MacDonald
1996-09-23 0:00 ` Dik T. Winter
1996-09-25 0:00 ` John Harper
1996-09-25 0:00 ` jupiter
1996-09-24 0:00 ` language wars (results 13 September) last posting Andrew Gierth
1996-09-24 0:00 ` Art Schwarz
-- strict thread matches above, loose matches on Subject: below --
1996-09-25 0:00 Friday 13th, try it yourself (was Language Wars..) Barrie Walker
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