jd.f

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      function jd(i,j,k)
c
c
c    This function converts a calendar date to the corresponding Julian
c    day starting at noon on the calendar date.  The algorithm used is
c    from Van Flandern and Pulkkinen, Ap. J. Supplement Series 41, 
c    November 1979, p. 400.
c
c
c       Arguments
c     
c       Name    Type    I/O     Description
c       ----    ----    ---     -----------
c       i       I*4      I      Year - e.g. 1970
c       j       I*4      I      Month - (1-12)
c       k       I*4      I      Day  - (1-31)
c       jd      I*4      O      Julian day
c
c     external references
c     -------------------
c      none
c
c
c     Written by Frederick S. Patt, GSC, November 4, 1992
c
c
        jd = 367*i - 7*(i+(j+9)/12)/4 + 275*j/9 + k + 1721014
 
c  This additional calculation is needed only for dates outside of the 
c   period March 1, 1900 to February 28, 2100
c       jd = jd + 15 - 3*((i+(j-9)/7)/100+1)/4
        return
        end