Procedure

     GFREFN ( GF, default refinement estimator )

     SUBROUTINE GFREFN ( T1, T2, S1, S2, T )

Abstract

     Estimate, using a bisection method, the next abscissa value at
     which a state change occurs. This is the default GF refinement
     method.

Required_Reading

     None.

Keywords

     SEARCH
     UTILITY

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION      T1
     DOUBLE PRECISION      T2
     LOGICAL               S1
     LOGICAL               S2
     DOUBLE PRECISION      T

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     T1         I   One of two values bracketing a state change.
     T2         I   The other value that brackets a state change.
     S1         I   State at T1.
     S2         I   State at T2.
     T          O   New value at which to check for transition.

Detailed_Input

     T1       is one of two abscissa values (usually times)
              bracketing a state change.

     T2       is the other abscissa value that brackets a state change.

     S1       is the system state at T1. This argument is provided
              for forward compatibility; it's not currently used.

     S2       is the system state at T2. This argument is provided
              for forward compatibility; it's not currently used.

Detailed_Output

     T        is the midpoint of T1 and T2.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     "Refinement" means reducing the size of a bracketing interval on
     the real line in which a solution is known to lie. In the GF
     setting, the solution is the time of a state transition of a
     binary function.

     This routine supports solving for locations of bracketed state
     transitions by the bisection method. This is the default
     refinement method used by the GF system.

     The argument list of this routine is compatible with the GF
     system's general root finding routine. Refinement routines created
     by users must have the same argument list in order to be used by
     the GF mid-level APIs such as GFOCCE and GFFOVE.

Examples

     The following code fragment from an example program in the header
     of GFOCCE shows the routine passed as the 12th argument.

        C
        C     Define as EXTERNAL the routines to pass to GFOCCE.
        C
              EXTERNAL              GFSTEP
              EXTERNAL              GFREFN
              EXTERNAL              GFREPI
              EXTERNAL              GFREPU
              EXTERNAL              GFREPF
              EXTERNAL              GFBAIL

                 ... initialize for the search ...

              CALL GFOCCE ( 'ANY',
             .              'MOON',   'ellipsoid',  'IAU_MOON',
             .              'SUN',    'ellipsoid',  'IAU_SUN',
             .              'LT',     'EARTH',       CNVTOL,
             .               GFSTEP,   GFREFN,       RPT,
             .               GFREPI,   GFREPU,       GFREPF,
             .               BAIL,     GFBAIL,       CNFINE,  RESULT )

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.0.1, 26-OCT-2021 (JDR)

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.0, 03-MAR-2009 (NJB) (EDW)