REAL *8 FUNCTION JD ( IDAY, IMON, IYEAR )
C
C           Returns the julian day for 0 hours ut.
      IMPLICIT UNDEFINED(A-Z)
      SAVE
      INTEGER *4 IDAY, IMON, IYEAR, YEAR0, YEAR1, DOY
      PARAMETER (YEAR0=1986)
      PARAMETER (YEAR1=1995)
      REAL *8 JD0(YEAR0:YEAR1)
      EXTERNAL DOY
      DATA JD0 / 2446430.5D0,  2446795.5D0, 2447160.5, 2447526.5,
     $           2447891.5D0,  2448256.5D0, 2448621.5, 2448987.5,
     $           2449352.5D0,  2449717.5D0 /
      IF (( IYEAR .LT. YEAR0 ).OR.( IYEAR .GT. YEAR1 ) ) THEN
          WRITE(0,'(A,I5)') ' INVALID YEAR FOR COMPUTING JD:', IYEAR
      ELSE
          JD = JD0(IYEAR) + DOY( IDAY, IMON, IYEAR )
      END IF
      RETURN
      END
      INTEGER *4 FUNCTION DOY( IDAY, IMON, IYEAR )
C
C     Returns Day of Year for date in arguements ( 1 Jan => doy=1 )
      IMPLICIT UNDEFINED(A-Z)
      SAVE
      INTEGER *4 IDAY, IMON, IYEAR, LEAP, I, NDAY(12,0:1)
      DATA NDAY / 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30,
     $            0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30 /
C        LEAP=0 for leap lear
      LEAP = MIN( 1, MOD( IYEAR, 4 ) )
      DOY = IDAY
      DO 100 I = 1, IMON
          DOY = DOY + NDAY(I, LEAP)
  100 CONTINUE
      RETURN
      END
      SUBROUTINE NEXTDAY ( IDAY, IMON, IYEAR )
C
C   Increments the date by one
C
      IMPLICIT UNDEFINED(A-Z)
      INTEGER *4 IDAY, IMON, IYEAR, DAYS(12,0:1), LEAP
      DATA DAYS / 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
     $            31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 /
      LEAP = MIN ( 1, MOD( IYEAR, 4 ) )
      IDAY = IDAY + 1
      IF ( IDAY .GT. DAYS(IMON,LEAP) ) THEN
          IMON = IMON + 1
          IDAY = 1
          IF ( IMON .EQ. 13 ) THEN
              IMON = 1
              IYEAR = IYEAR + 1
          END IF
      END IF
      RETURN
      END