Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / financial-0.4.0 / easter.m

diff --git a/octave_packages/financial-0.4.0/easter.m b/octave_packages/financial-0.4.0/easter.m
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+## Copyright (C) 2008 Bill Denney <bill@denney.ws>
+##
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[m, d] =} easter (y)
+## @deftypefnx {Function File} {datenum =} easter (y)
+##
+## Return the month (@var{m}) and day (@var{d}) of Easter in the
+## Gregorial calendar on a given year or years.
+##
+## @seealso{holidays}
+## @end deftypefn
+
+function varargout = easter (y)
+
+  ## This uses the Meesus/Jones/Butcher Gregorian algorithm as described
+  ## on http://en.wikipedia.org/wiki/Computus#Algorithms
+  a = mod (y, 19);
+  b = floor (y/100);
+  c = mod (y, 100);
+  d = floor (b/4);
+  e = mod (b, 4);
+  f = floor ((b + 8)/25);
+  g = floor ((b - f + 1)/3);
+  h = mod ((19*a+b-d-g+15), 30);
+  i = floor (c/4);
+  k = mod (c, 4);
+  L = mod ((32 + 2*e + 2*i - h - k), 7);
+  m = floor ((a + 11*h + 22*L)/451);
+  mon = floor ((h + L - 7*m + 114)/31);
+  day = 1 + mod ((h + L - 7*m + 114), 31);
+
+  if nargout == 2
+       varargout = {mon(:), day(:)};
+  else
+       varargout{1} = reshape (datenum (y(:), mon(:), day(:)), size (y));
+  end
+
+endfunction
+
+## Tests
+## Validate that it calculates the correct date for a decade
+%!assert(easter(1990), datenum(1990, 4, 15))
+%!assert(easter(1991), datenum(1991, 3, 31))
+%!assert(easter(1992), datenum(1992, 4, 19))
+%!assert(easter(1993), datenum(1993, 4, 11))
+%!assert(easter(1994), datenum(1994, 4, 3))
+%!assert(easter(1995), datenum(1995, 4, 16))
+%!assert(easter(1996), datenum(1996, 4, 7))
+%!assert(easter(1997), datenum(1997, 3, 30))
+%!assert(easter(1998), datenum(1998, 4, 12))
+%!assert(easter(1999), datenum(1999, 4, 4))
+## Validate vector and matrix inputs
+%!assert(easter([2000 2001]), [datenum(2000, 4, 23) datenum(2001, 4, 15)])
+%!assert(easter([2002;2003]), [datenum(2002, 3, 31);datenum(2003, 4, 20)])
+%!assert(easter([2004 2005;2006 2007;2008 2009]), [datenum(2004, 4, 11) datenum(2005, 3, 27);datenum(2006, 4, 16) datenum(2007, 4, 8);datenum(2008, 3, 23) datenum(2009, 4, 12)])
+%!assert(easter([2002;2003]), [datenum(2002, 3, 31);datenum(2003, 4, 20)])