NASA Ocean Color

ocssw V2022

       SUBROUTINE kozsak2(IFLAG,GE,RE,AJ2,X,XN,XI,IER)
  
 C $Header: /app/shared/RCS/irix-5.2/seawifsd/src/mops/mopsV4.1/swfnav/kozsak2.f,v 1.1 1995/01/17 23:02:23 seawifsd Exp seawifsd $
 C $Log: kozsak2.f,v $
 C Revision 1.1  1995/01/17 23:02:23  seawifsd
 C Initial revision
 C                                                                        
 C  VERSION 4/28/88
 C  PURPOSE
 C    CONVERTS BETWEEN MEAN AND OSCULATING ORBITAL ELEMENTS
 C  INPUT
 C    IFLAG   = 1, MEAN TO OSCULATING
 C            = 2, OSCULATING TO MEAN
 C            = 3, OSCULATING TO MEAN WITH INITIAL GUESS FOR MEAN
 C    GE      = PRODUCT OF GRAVITATIONAL CONSTANT * MASS OF
 C              PLANET (KM**3/SEC**2)
 C    RE      = RADIUS OF PLANET (KM)
 C    AJ2     = J2 = -C20
 C    X       = AN ARRAY OF 6 ORBITAL ELEMENTS, A, E, I, NODE, W, AND M
 C              (KM, RAD)
 C    XI      = AN ARRAY OF 6 INITIAL MEAN ELEMENTS
 C  OUTPUT ARGUMENTS
 C    XN      = AN ARRAY OF 6 ORBITAL ELEMENTS AFTER CONVERSION
 C    IER     = ERROR FLAG (SET TO 1 IF OSCULATING-TO-MEAN CONVERSION
 C               DOES NOT CONVERGE)
 C  CALL SUBROUTINES
 C    DELM
 C  REFERENCES
 C    JPL IOM 312/85.2-927, 23 JANUARY 1985, BY C. UPHOFF
 C    JPL EM 312/87-153, 20 APRIL 1987
 C  ANALYSIS
 C    JOHNNY H. KWOK - JPL
 C  PROGRAMMER
 C    JOHNNY H. KWOK - JPL
 C  MODIFICATIONS
 C    ADDED OPTION TO INPUT INITIAL GUESS AT MEAN ELEMENTS FOR 
 C    OSCULATING-TO-MEAN CONVERSION AND CONVERGENCE TEST FOR CONVERSION
 C    F.S. PATT, GSC, 29 NOVEMBER 1993
 C
 C    CHANGED MAXIMUM NUMBER OF ITERATIONS TO 200 AND INITIALIZED ERROR
 C    RETURN CODE.  F.S. PATT, GSC, OCTOBER 26, 1993
 C
 C  COMMENTS
 C    THIS PROGRAM USES AN ALGORITHM DERIVED BY C. UPHOFF (REF) WHICH
 C    USES A COMBINATION OF KOZAI'S AND IZSAK'S THEORY.
 C
       IMPLICIT DOUBLE PRECISION (a-h,o-z)
       dimension x(6),xn(6),xi(6),dx(6),xtol(6)
       LOGICAL DONE
       DATA tpi/6.283185307179586d0/
       DATA zero/0.d0/,rtol/1.d-6/
       DATA xtol/1.d-5,1.d-8,2*1.d-7,2*1.d-5/
       pi = tpi/2.d0
       p3o2 = 3.d0*tpi/2.d0
 C      IMAX=5
 C      IF (X(2).LT.1.D-1) IMAX=10
 C      IF (X(2).LT.1.D-2) IMAX=20
 C      IF (X(2).LT.1.D-3) IMAX=30
       imax = 200
       ier = 0
       IF (iflag.NE.3) THEN
         DO i=1,6
           xi(i)=x(i)
         END DO
       END IF
       icount=0
 c       print *,' '
 c       print *,x
       IF (iflag.GT.1) THEN
         done = .false.
         DO WHILE ((.NOT.done).AND.(icount.LT.imax))
           CALL delm(re,ge,aj2,xi,dx)
           DO i=3,6
             dx(i)=dmod(dx(i)+p3o2,tpi)-pi
           END DO
 c         print *,dx
           icount = icount + 1
           fac = 0.5*(1.d0-abs(dx(5))/pi)
           done = .true.
           DO i=1,6
             xdel = (x(i)-dx(i)-xi(i))
             IF (i.GE.3) xdel = dmod(xdel+p3o2,tpi)-pi
             rdel = xdel/dx(i)
             IF ((abs(xdel).GT.xtol(i)).AND.(abs(rdel).GT.rtol)) 
      *        done = .false.
             xn(i)=xi(i) + xdel*fac
           END DO
           IF (xn(2).LT.zero) xn(2)=zero
 c      DO 30 I=3,6
 c   30 XN(I)=DMOD(XN(I)+TPI,TPI)
           DO i=1,6
             xi(i)=xn(i)
           END DO
         ENDDO
         print *,'KOZSAK2:  Mean elements converged in ',icount,
      *    ' iterations'
         IF (icount.EQ.imax) ier = 1
       ELSE
         CALL delm(re,ge,aj2,xi,dx)
         DO i=1,6
           xn(i)=xi(i)+dx(i)
         ENDDO
       ENDIF
   900 CONTINUE
       DO i=3,6
         xn(i)=dmod(xn(i)+tpi,tpi)
       END DO
       RETURN
       END