julian

 JULIAN converts Gregorian calendar dates to corresponding Julian day numbers.

 [j]=JULIAN(y,m,d,h) 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 Z, May 23, 1968.
 
   INPUT:  d -  day (1-31) component of Gregorian date
           m -  month (1-12) component
           y -  year (e.g., 1979) component
           h -  decimal hours (assumed 0 if absent)
   
   OUTPUT: j - decimal Julian day number (e.g., 0000Z Jan 1 is 0.0)
 
   Usage: [j]=julian(y,m,d,h)  or  [j]=julian([y m d hour min sec])

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 ver. 1: 5/15/91 (RS)
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0001    function [j]=julian(y,m,d,h)
0002 
0003 % JULIAN converts Gregorian calendar dates to corresponding Julian day numbers.
0004 %
0005 % [j]=JULIAN(y,m,d,h) converts Gregorian calendar dates to corresponding
0006 % Julian day numbers.  Although the formal definition holds that Julian
0007 % days start and end at noon, here Julian days start and end at midnight.
0008 % In this convention, Julian day 2440000 began at 0000 Z, May 23, 1968.
0009 %
0010 %   INPUT:  d -  day (1-31) component of Gregorian date
0011 %           m -  month (1-12) component
0012 %           y -  year (e.g., 1979) component
0013 %           h -  decimal hours (assumed 0 if absent)
0014 %
0015 %   OUTPUT: j - decimal Julian day number (e.g., 0000Z Jan 1 is 0.0)
0016 %
0017 %   Usage: [j]=julian(y,m,d,h)  or  [j]=julian([y m d hour min sec])
0018 %
0019 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0020 % ver. 1: 5/15/91 (RS)
0021 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0022      
0023     if nargin==3,
0024         h=0.;
0025       elseif nargin==1,
0026         h=hms2h(y(4),y(5),y(6));
0027         d=y(3);
0028         m=y(2);
0029         y=y(1);
0030       end
0031       mo=m+9;
0032       yr=y-1;
0033       i=(m>2);
0034       mo(i)=m(i)-3;
0035       yr(i)=y(i); 
0036       c = floor(yr/100);
0037       yr = yr - c*100;
0038       j = floor((146097*c)/4) + floor((1461*yr)/4) + ...
0039            floor((153*mo +2)/5) +d +1721119;
0040 
0041 %     If you want julian days to start and end at noon,
0042 %     replace the following line with:
0043 %     j=j+(h-12)/24;
0044  
0045       j=j+h/24;
0046       end