julian.m

function [j]=julian(y,m,d,h)
%JULIAN  Converts Gregorian calendar dates to corresponding
%      Julian day numbers.  Although the formal definition
%      holds that Julian days start and end at noon, here
%      Julian days start and end at midnight.
%
%    In this convention, Julian day 2440000 began at 0000 hours, May 23, 1968.
%
%
%     Usage: [j]=julian(y,m,d,h)  or  [j]=julian([y m d hour min sec])
%     ************************************************************
%
%        d.... day (1-31) component of Gregorian date
%        m.... month (1-12) component
%        y.... year (e.g., 1979) component
%        j.... decimal Julian day number
%        h.... decimal hours (assumed 0 if absent)
%
%     ************************************************************
%     recoded for MATLAB  by Rich Signell, 5-15-91
%
      if nargin==3,
        h=0.;
      elseif nargin==1,
        h=hms2h(y(:,4),y(:,5),y(:,6));
        d=y(:,3);
        m=y(:,2);
        y=y(:,1);
      end
      mo=m+9;
      yr=y-1;
      i=(m>2);
      mo(i)=m(i)-3;
      yr(i)=y(i); 
      c = floor(yr/100);
      yr = yr - c*100;
      j = floor((146097*c)/4) + floor((1461*yr)/4) + ...
           floor((153*mo +2)/5) +d +1721119;

%     If you want julian days to start and end at noon, 
%     replace the following line with:
%     j=j+(h-12)/24;
 
      j=j+h/24;

%==============================================================
function [hours]=hms2h(h,m,s);
%HMS2H converts hours, minutes, and seconds to hours
%
%  Usage:  [hours]=hms2h(h,m,s);   or [hours]=hms2h(hhmmss);
%
if nargin== 1,
   hms=h;
   h=floor(hms/10000);
   ms=hms-h*10000;
   m=floor(ms/100);
   s=ms-m*100;
   hours=h+m/60+s/3600;
else
   hours=h+(m+s/60)/60;
end