model/src/forward_step.F

C $Header: /u/gcmpack/MITgcm/model/src/forward_step.F,v 1.34 2002/07/13 04:59:42 heimbach Exp $
C $Name:  $

#include "CPP_OPTIONS.h"

CBOP
C     !ROUTINE: FORWARD_STEP
C     !INTERFACE:
      SUBROUTINE FORWARD_STEP( iloop, myTime, myIter, myThid )

C     !DESCRIPTION: \bv
C     *==================================================================
C     | SUBROUTINE forward_step
C     | o Run the ocean model and, optionally, evaluate a cost function.
C     *==================================================================
C     |
C     | THE_MAIN_LOOP is the toplevel routine for the Tangent Linear and
C     | Adjoint Model Compiler (TAMC). For this purpose the initialization
C     | of the model was split into two parts. Those parameters that do
C     | not depend on a specific model run are set in INITIALISE_FIXED,   
C     | whereas those that do depend on the specific realization are
C     | initialized in INITIALISE_VARIA.   
C     |
C     *==================================================================
C     \ev

C     !USES:
      IMPLICIT NONE
C     == Global variables ==
#include "SIZE.h"
#include "EEPARAMS.h"
#include "PARAMS.h"
#include "DYNVARS.h"
#include "FFIELDS.h"

#ifdef ALLOW_NONHYDROSTATIC
#include "CG3D.h"
#endif

#ifdef ALLOW_SHAP_FILT
#include "SHAP_FILT.h"
#endif
#ifdef ALLOW_ZONAL_FILT
#include "ZONAL_FILT.h"
#endif

#ifdef ALLOW_AUTODIFF_TAMC
# include "tamc.h"
# include "ctrl.h"
# include "ctrl_dummy.h"
# include "cost.h"
# ifdef INCLUDE_EXTERNAL_FORCING_PACKAGE
#  include "exf_fields.h"
#  ifdef ALLOW_BULKFORMULAE
#   include "exf_constants.h"
#  endif
# endif
# ifdef ALLOW_OBCS
#  include "OBCS.h"
# endif
#endif

C     !LOCAL VARIABLES:
C     == Routine arguments ==
C     note: under the multi-threaded model myiter and 
C           mytime are local variables passed around as routine 
C           arguments. Although this is fiddly it saves the need to 
C           impose additional synchronisation points when they are 
C           updated.
C     myiter - iteration counter for this thread
C     mytime - time counter for this thread
C     mythid - thread number for this instance of the routine.
      integer iloop
      integer mythid 
      integer myiter
      _RL     mytime
      INTEGER bi,bj

CEOP


#ifdef ALLOW_AUTODIFF_TAMC
C--     Reset the model iteration counter and the model time.
        myiter = nIter0 + (iloop-1)
        mytime = startTime + float(iloop-1)*deltaTclock
#endif

#if (defined (ALLOW_AUTODIFF_TAMC) && defined (ALLOW_AUTODIFF_MONITOR))
C       Include call to a dummy routine. Its adjoint will be 
C       called at the proper place in the adjoint code.
C       The adjoint routine will print out adjoint values 
C       if requested. The location of the call is important, 
C       it has to be after the adjoint of the exchanges 
C       (DO_GTERM_BLOCKING_EXCHANGES).
        CALL DUMMY_IN_STEPPING( myTime, myIter, myThid )
        CALL DO_FIELDS_BLOCKING_EXCHANGES( myThid )
#endif

#ifdef EXACT_CONSERV
      IF (exactConserv) THEN
C--   Update etaH(n+1) :
         CALL UPDATE_ETAH( myTime, myIter, myThid )
      ENDIF
#endif /* EXACT_CONSERV */ 

#ifdef NONLIN_FRSURF
C--   compute the future surface level thickness
C      according to etaH(n+1) 
        IF ( nonlinFreeSurf.GT.0) THEN
          CALL CALC_SURF_DR(etaH, myTime, myIter, myThid )
        ENDIF
#endif /* NONLIN_FRSURF */

C--     Load forcing/external data fields.
#ifdef INCLUDE_EXTERNAL_FORCING_PACKAGE
C       NOTE, that although the exf package is part of the
C       distribution, it is not currently maintained, i.e.
C       exf is disabled by default in genmake.
#ifdef ALLOW_AUTODIFF_TAMC
c**************************************
#include "checkpoint_lev1_directives.h"
c**************************************
#endif
        CALL EXF_GETFORCING( mytime, myiter, mythid )
#else
        CALL TIMER_START('EXTERNAL_FIELDS_LOAD[THE_MAIN_LOOP]',mythid)
        CALL EXTERNAL_FIELDS_LOAD( mytime, myiter, mythid )
        CALL TIMER_STOP ('EXTERNAL_FIELDS_LOAD[THE_MAIN_LOOP]',mythid)
#endif

C--     Step forward fields and calculate time tendency terms.
        CALL TIMER_START('THERMODYNAMICS      [THE_MAIN_LOOP]',mythid)
        CALL THERMODYNAMICS( myTime, myIter, myThid )
        CALL TIMER_STOP ('THERMODYNAMICS      [THE_MAIN_LOOP]',mythid)

C--   do exchanges (needed for DYNAMICS) when using stagger time-step :
        CALL TIMER_START('BLOCKING_EXCHANGES  [THE_MAIN_LOOP]',myThid)
        CALL DO_STAGGER_FIELDS_EXCHANGES( myTime, myIter, myThid )
        CALL TIMER_STOP ('BLOCKING_EXCHANGES  [THE_MAIN_LOOP]',myThid)

#ifdef ALLOW_SHAP_FILT
       IF (useSHAP_FILT .AND. 
     &     staggerTimeStep .AND. shap_filt_TrStagg ) THEN
        CALL TIMER_START('SHAP_FILT           [THE_MAIN_LOOP]',myThid)
        CALL SHAP_FILT_APPLY_TS( gT, gS, myTime, myIter, myThid )
        CALL TIMER_STOP ('SHAP_FILT           [THE_MAIN_LOOP]',myThid)
       ENDIF
#endif
#ifdef ALLOW_ZONAL_FILT
       IF (useZONAL_FILT .AND. 
     &     staggerTimeStep .AND. zonal_filt_TrStagg ) THEN
        CALL TIMER_START('ZONAL_FILT_APPLY    [THE_MAIN_LOOP]',myThid)
        CALL ZONAL_FILT_APPLY_TS( gT, gS, myThid )
        CALL TIMER_STOP ('ZONAL_FILT_APPLY    [THE_MAIN_LOOP]',myThid)
      ENDIF
#endif   

C--     Step forward fields and calculate time tendency terms.
        IF ( momStepping ) THEN
        CALL TIMER_START('DYNAMICS            [THE_MAIN_LOOP]',mythid)
        CALL DYNAMICS( myTime, myIter, myThid )
        CALL TIMER_STOP ('DYNAMICS            [THE_MAIN_LOOP]',mythid)
        ENDIF

#ifdef ALLOW_NONHYDROSTATIC
C--   Step forward W field in N-H algorithm
        IF ( momStepping .AND. nonHydrostatic ) THEN
          CALL TIMER_START('CALC_GW          [THE_MAIN_LOOP]',myThid)
          CALL CALC_GW(myThid)
          CALL TIMER_STOP ('CALC_GW          [THE_MAIN_LOOP]',myThid)
        ENDIF
#endif

#ifdef NONLIN_FRSURF
C--   update hfacC,W,S and recip_hFac according to etaH(n+1) :
      IF ( nonlinFreeSurf.GT.0) THEN
        CALL UPDATE_SURF_DR( myTime, myIter, myThid )
      ENDIF
C-    update also CG2D matrix (and preconditioner)
      IF ( momStepping .AND. nonlinFreeSurf.GT.2 ) THEN
        CALL UPDATE_CG2D( myTime, myIter, myThid )
      ENDIF
#endif

C--   Apply Filters to u*,v* before SOLVE_FOR_PRESSURE
#ifdef ALLOW_SHAP_FILT
      IF (useSHAP_FILT .AND. shap_filt_uvStar) THEN
        CALL TIMER_START('SHAP_FILT           [THE_MAIN_LOOP]',myThid)
        CALL SHAP_FILT_APPLY_UV( gUnm1,gVnm1, myTime,myIter,myThid )
        IF (implicDiv2Dflow.LT.1.) THEN
C--   Explicit+Implicit part of the Barotropic Flow Divergence
C      => Filtering of uVel,vVel is necessary
          CALL SHAP_FILT_APPLY_UV( uVel,vVel, myTime,myIter,myThid )
        ENDIF
        CALL TIMER_STOP ('SHAP_FILT           [THE_MAIN_LOOP]',myThid)
      ENDIF
#endif
#ifdef ALLOW_ZONAL_FILT
      IF (useZONAL_FILT .AND. zonal_filt_uvStar) THEN
        CALL TIMER_START('ZONAL_FILT_APPLY    [THE_MAIN_LOOP]',myThid)
        CALL ZONAL_FILT_APPLY_UV( gUnm1, gVnm1, myThid )
        IF (implicDiv2Dflow.LT.1.) THEN
C--   Explicit+Implicit part of the Barotropic Flow Divergence
C      => Filtering of uVel,vVel is necessary
          CALL ZONAL_FILT_APPLY_UV( uVel, vVel, myThid )
        ENDIF
        CALL TIMER_STOP ('ZONAL_FILT_APPLY    [THE_MAIN_LOOP]',myThid)
      ENDIF
#endif  

C--   Solve elliptic equation(s).
C     Two-dimensional only for conventional hydrostatic or 
C     three-dimensional for non-hydrostatic and/or IGW scheme.
      IF ( momStepping ) THEN
      CALL TIMER_START('SOLVE_FOR_PRESSURE  [THE_MAIN_LOOP]',myThid)
      CALL SOLVE_FOR_PRESSURE(myTime, myIter, myThid)
      CALL TIMER_STOP ('SOLVE_FOR_PRESSURE  [THE_MAIN_LOOP]',myThid)
      ENDIF

C--   Correct divergence in flow field and cycle time-stepping
C     arrays (for all fields) ; update time-counter
      myIter = nIter0 + iLoop
      myTime = startTime + deltaTClock * float(iLoop)
      CALL TIMER_START('THE_CORRECTION_STEP [THE_MAIN_LOOP]',myThid)
      CALL THE_CORRECTION_STEP(myTime, myIter, myThid)
      CALL TIMER_STOP ('THE_CORRECTION_STEP [THE_MAIN_LOOP]',myThid)

C--   Do "blocking" sends and receives for tendency "overlap" terms
c     CALL TIMER_START('BLOCKING_EXCHANGES  [THE_MAIN_LOOP]',myThid)
c     CALL DO_GTERM_BLOCKING_EXCHANGES( myThid )
c     CALL TIMER_STOP ('BLOCKING_EXCHANGES  [THE_MAIN_LOOP]',myThid)

C--   Do "blocking" sends and receives for field "overlap" terms
      CALL TIMER_START('BLOCKING_EXCHANGES  [THE_MAIN_LOOP]',myThid)
      CALL DO_FIELDS_BLOCKING_EXCHANGES( myThid )
      CALL TIMER_STOP ('BLOCKING_EXCHANGES  [THE_MAIN_LOOP]',myThid)

#ifdef ALLOW_FLT
C--   Calculate float trajectories
      IF (useFLT) THEN
        CALL TIMER_START('FLOATS            [THE_MAIN_LOOP]',myThid)
        CALL FLT_MAIN(myIter,myTime, myThid)
        CALL TIMER_STOP ('FLOATS            [THE_MAIN_LOOP]',myThid)
      ENDIF
#endif

#ifndef EXCLUDE_MONITOR
C--   Check status of solution (statistics, cfl, etc...)
      CALL MONITOR( myIter, myTime, myThid )
#endif /* EXCLUDE_MONITOR */

C--   Do IO if needed.
      CALL TIMER_START('DO_THE_MODEL_IO     [THE_MAIN_LOOP]',myThid)
      CALL DO_THE_MODEL_IO( myTime, myIter, myThid )
      CALL TIMER_STOP ('DO_THE_MODEL_IO     [THE_MAIN_LOOP]',myThid)

C--   Save state for restarts
C     Note:    (jmc: is it still the case after ckp35 ?)
C     =====
C     Because of the ordering of the timestepping code and
C     tendency term code at end of loop model arrays hold
C     U,V,T,S  at "time-level" N but gu, gv, gs, gt, guNM1,... 
C     at "time-level" N+1/2 (guNM1 at "time-level" N+1/2 is 
C     gu at "time-level" N-1/2) and etaN at "time-level" N+1/2.
C      where N = I+timeLevBase-1
C     Thus a checkpoint contains U.0000000000, GU.0000000001 and 
C     etaN.0000000001 in the indexing scheme used for the model 
C     "state" files. This example is referred to as a checkpoint 
C     at time level 1 
      CALL TIMER_START('WRITE_CHECKPOINT    [THE_MAIN_LOOP]',myThid)
      CALL WRITE_CHECKPOINT(
     &        .FALSE., myTime, myIter, myThid )
      CALL TIMER_STOP ('WRITE_CHECKPOINT    [THE_MAIN_LOOP]',myThid)

      END
1	C $Header: /u/gcmpack/MITgcm/model/src/forward_step.F,v 1.34 2002/07/13 04:59:42 heimbach Exp $
2	C $Name: $
3
4	#include "CPP_OPTIONS.h"
5
6	CBOP
7	C !ROUTINE: FORWARD_STEP
8	C !INTERFACE:
9	SUBROUTINE FORWARD_STEP( iloop, myTime, myIter, myThid )
10
11	C !DESCRIPTION: \bv
12	C *==================================================================
13	C \| SUBROUTINE forward_step
14	C \| o Run the ocean model and, optionally, evaluate a cost function.
15	C *==================================================================
16	C \|
17	C \| THE_MAIN_LOOP is the toplevel routine for the Tangent Linear and
18	C \| Adjoint Model Compiler (TAMC). For this purpose the initialization
19	C \| of the model was split into two parts. Those parameters that do
20	C \| not depend on a specific model run are set in INITIALISE_FIXED,
21	C \| whereas those that do depend on the specific realization are
22	C \| initialized in INITIALISE_VARIA.
23	C \|
24	C *==================================================================
25	C \ev
26
27	C !USES:
28	IMPLICIT NONE
29	C == Global variables ==
30	#include "SIZE.h"
31	#include "EEPARAMS.h"
32	#include "PARAMS.h"
33	#include "DYNVARS.h"
34	#include "FFIELDS.h"
35
36	#ifdef ALLOW_NONHYDROSTATIC
37	#include "CG3D.h"
38	#endif
39
40	#ifdef ALLOW_SHAP_FILT
41	#include "SHAP_FILT.h"
42	#endif
43	#ifdef ALLOW_ZONAL_FILT
44	#include "ZONAL_FILT.h"
45	#endif
46
47	#ifdef ALLOW_AUTODIFF_TAMC
48	# include "tamc.h"
49	# include "ctrl.h"
50	# include "ctrl_dummy.h"
51	# include "cost.h"
52	# ifdef INCLUDE_EXTERNAL_FORCING_PACKAGE
53	# include "exf_fields.h"
54	# ifdef ALLOW_BULKFORMULAE
55	# include "exf_constants.h"
56	# endif
57	# endif
58	# ifdef ALLOW_OBCS
59	# include "OBCS.h"
60	# endif
61	#endif
62
63	C !LOCAL VARIABLES:
64	C == Routine arguments ==
65	C note: under the multi-threaded model myiter and
66	C mytime are local variables passed around as routine
67	C arguments. Although this is fiddly it saves the need to
68	C impose additional synchronisation points when they are
69	C updated.
70	C myiter - iteration counter for this thread
71	C mytime - time counter for this thread
72	C mythid - thread number for this instance of the routine.
73	integer iloop
74	integer mythid
75	integer myiter
76	_RL mytime
77	INTEGER bi,bj
78
79	CEOP
80
81
82	#ifdef ALLOW_AUTODIFF_TAMC
83	C-- Reset the model iteration counter and the model time.
84	myiter = nIter0 + (iloop-1)
85	mytime = startTime + float(iloop-1)*deltaTclock
86	#endif
87
88	#if (defined (ALLOW_AUTODIFF_TAMC) && defined (ALLOW_AUTODIFF_MONITOR))
89	C Include call to a dummy routine. Its adjoint will be
90	C called at the proper place in the adjoint code.
91	C The adjoint routine will print out adjoint values
92	C if requested. The location of the call is important,
93	C it has to be after the adjoint of the exchanges
94	C (DO_GTERM_BLOCKING_EXCHANGES).
95	CALL DUMMY_IN_STEPPING( myTime, myIter, myThid )
96	CALL DO_FIELDS_BLOCKING_EXCHANGES( myThid )
97	#endif
98
99	#ifdef EXACT_CONSERV
100	IF (exactConserv) THEN
101	C-- Update etaH(n+1) :
102	CALL UPDATE_ETAH( myTime, myIter, myThid )
103	ENDIF
104	#endif /* EXACT_CONSERV */
105
106	#ifdef NONLIN_FRSURF
107	C-- compute the future surface level thickness
108	C according to etaH(n+1)
109	IF ( nonlinFreeSurf.GT.0) THEN
110	CALL CALC_SURF_DR(etaH, myTime, myIter, myThid )
111	ENDIF
112	#endif /* NONLIN_FRSURF */
113
114	C-- Load forcing/external data fields.
115	#ifdef INCLUDE_EXTERNAL_FORCING_PACKAGE
116	C NOTE, that although the exf package is part of the
117	C distribution, it is not currently maintained, i.e.
118	C exf is disabled by default in genmake.
119	#ifdef ALLOW_AUTODIFF_TAMC
120	c**************************************
121	#include "checkpoint_lev1_directives.h"
122	c**************************************
123	#endif
124	CALL EXF_GETFORCING( mytime, myiter, mythid )
125	#else
126	CALL TIMER_START('EXTERNAL_FIELDS_LOAD[THE_MAIN_LOOP]',mythid)
127	CALL EXTERNAL_FIELDS_LOAD( mytime, myiter, mythid )
128	CALL TIMER_STOP ('EXTERNAL_FIELDS_LOAD[THE_MAIN_LOOP]',mythid)
129	#endif
130
131	C-- Step forward fields and calculate time tendency terms.
132	CALL TIMER_START('THERMODYNAMICS [THE_MAIN_LOOP]',mythid)
133	CALL THERMODYNAMICS( myTime, myIter, myThid )
134	CALL TIMER_STOP ('THERMODYNAMICS [THE_MAIN_LOOP]',mythid)
135
136	C-- do exchanges (needed for DYNAMICS) when using stagger time-step :
137	CALL TIMER_START('BLOCKING_EXCHANGES [THE_MAIN_LOOP]',myThid)
138	CALL DO_STAGGER_FIELDS_EXCHANGES( myTime, myIter, myThid )
139	CALL TIMER_STOP ('BLOCKING_EXCHANGES [THE_MAIN_LOOP]',myThid)
140
141	#ifdef ALLOW_SHAP_FILT
142	IF (useSHAP_FILT .AND.
143	& staggerTimeStep .AND. shap_filt_TrStagg ) THEN
144	CALL TIMER_START('SHAP_FILT [THE_MAIN_LOOP]',myThid)
145	CALL SHAP_FILT_APPLY_TS( gT, gS, myTime, myIter, myThid )
146	CALL TIMER_STOP ('SHAP_FILT [THE_MAIN_LOOP]',myThid)
147	ENDIF
148	#endif
149	#ifdef ALLOW_ZONAL_FILT
150	IF (useZONAL_FILT .AND.
151	& staggerTimeStep .AND. zonal_filt_TrStagg ) THEN
152	CALL TIMER_START('ZONAL_FILT_APPLY [THE_MAIN_LOOP]',myThid)
153	CALL ZONAL_FILT_APPLY_TS( gT, gS, myThid )
154	CALL TIMER_STOP ('ZONAL_FILT_APPLY [THE_MAIN_LOOP]',myThid)
155	ENDIF
156	#endif
157
158	C-- Step forward fields and calculate time tendency terms.
159	IF ( momStepping ) THEN
160	CALL TIMER_START('DYNAMICS [THE_MAIN_LOOP]',mythid)
161	CALL DYNAMICS( myTime, myIter, myThid )
162	CALL TIMER_STOP ('DYNAMICS [THE_MAIN_LOOP]',mythid)
163	ENDIF
164
165	#ifdef ALLOW_NONHYDROSTATIC
166	C-- Step forward W field in N-H algorithm
167	IF ( momStepping .AND. nonHydrostatic ) THEN
168	CALL TIMER_START('CALC_GW [THE_MAIN_LOOP]',myThid)
169	CALL CALC_GW(myThid)
170	CALL TIMER_STOP ('CALC_GW [THE_MAIN_LOOP]',myThid)
171	ENDIF
172	#endif
173
174	#ifdef NONLIN_FRSURF
175	C-- update hfacC,W,S and recip_hFac according to etaH(n+1) :
176	IF ( nonlinFreeSurf.GT.0) THEN
177	CALL UPDATE_SURF_DR( myTime, myIter, myThid )
178	ENDIF
179	C- update also CG2D matrix (and preconditioner)
180	IF ( momStepping .AND. nonlinFreeSurf.GT.2 ) THEN
181	CALL UPDATE_CG2D( myTime, myIter, myThid )
182	ENDIF
183	#endif
184
185	C-- Apply Filters to u,v before SOLVE_FOR_PRESSURE
186	#ifdef ALLOW_SHAP_FILT
187	IF (useSHAP_FILT .AND. shap_filt_uvStar) THEN
188	CALL TIMER_START('SHAP_FILT [THE_MAIN_LOOP]',myThid)
189	CALL SHAP_FILT_APPLY_UV( gUnm1,gVnm1, myTime,myIter,myThid )
190	IF (implicDiv2Dflow.LT.1.) THEN
191	C-- Explicit+Implicit part of the Barotropic Flow Divergence
192	C => Filtering of uVel,vVel is necessary
193	CALL SHAP_FILT_APPLY_UV( uVel,vVel, myTime,myIter,myThid )
194	ENDIF
195	CALL TIMER_STOP ('SHAP_FILT [THE_MAIN_LOOP]',myThid)
196	ENDIF
197	#endif
198	#ifdef ALLOW_ZONAL_FILT
199	IF (useZONAL_FILT .AND. zonal_filt_uvStar) THEN
200	CALL TIMER_START('ZONAL_FILT_APPLY [THE_MAIN_LOOP]',myThid)
201	CALL ZONAL_FILT_APPLY_UV( gUnm1, gVnm1, myThid )
202	IF (implicDiv2Dflow.LT.1.) THEN
203	C-- Explicit+Implicit part of the Barotropic Flow Divergence
204	C => Filtering of uVel,vVel is necessary
205	CALL ZONAL_FILT_APPLY_UV( uVel, vVel, myThid )
206	ENDIF
207	CALL TIMER_STOP ('ZONAL_FILT_APPLY [THE_MAIN_LOOP]',myThid)
208	ENDIF
209	#endif
210
211	C-- Solve elliptic equation(s).
212	C Two-dimensional only for conventional hydrostatic or
213	C three-dimensional for non-hydrostatic and/or IGW scheme.
214	IF ( momStepping ) THEN
215	CALL TIMER_START('SOLVE_FOR_PRESSURE [THE_MAIN_LOOP]',myThid)
216	CALL SOLVE_FOR_PRESSURE(myTime, myIter, myThid)
217	CALL TIMER_STOP ('SOLVE_FOR_PRESSURE [THE_MAIN_LOOP]',myThid)
218	ENDIF
219
220	C-- Correct divergence in flow field and cycle time-stepping
221	C arrays (for all fields) ; update time-counter
222	myIter = nIter0 + iLoop
223	myTime = startTime + deltaTClock * float(iLoop)
224	CALL TIMER_START('THE_CORRECTION_STEP [THE_MAIN_LOOP]',myThid)
225	CALL THE_CORRECTION_STEP(myTime, myIter, myThid)
226	CALL TIMER_STOP ('THE_CORRECTION_STEP [THE_MAIN_LOOP]',myThid)
227
228	C-- Do "blocking" sends and receives for tendency "overlap" terms
229	c CALL TIMER_START('BLOCKING_EXCHANGES [THE_MAIN_LOOP]',myThid)
230	c CALL DO_GTERM_BLOCKING_EXCHANGES( myThid )
231	c CALL TIMER_STOP ('BLOCKING_EXCHANGES [THE_MAIN_LOOP]',myThid)
232
233	C-- Do "blocking" sends and receives for field "overlap" terms
234	CALL TIMER_START('BLOCKING_EXCHANGES [THE_MAIN_LOOP]',myThid)
235	CALL DO_FIELDS_BLOCKING_EXCHANGES( myThid )
236	CALL TIMER_STOP ('BLOCKING_EXCHANGES [THE_MAIN_LOOP]',myThid)
237
238	#ifdef ALLOW_FLT
239	C-- Calculate float trajectories
240	IF (useFLT) THEN
241	CALL TIMER_START('FLOATS [THE_MAIN_LOOP]',myThid)
242	CALL FLT_MAIN(myIter,myTime, myThid)
243	CALL TIMER_STOP ('FLOATS [THE_MAIN_LOOP]',myThid)
244	ENDIF
245	#endif
246
247	#ifndef EXCLUDE_MONITOR
248	C-- Check status of solution (statistics, cfl, etc...)
249	CALL MONITOR( myIter, myTime, myThid )
250	#endif /* EXCLUDE_MONITOR */
251
252	C-- Do IO if needed.
253	CALL TIMER_START('DO_THE_MODEL_IO [THE_MAIN_LOOP]',myThid)
254	CALL DO_THE_MODEL_IO( myTime, myIter, myThid )
255	CALL TIMER_STOP ('DO_THE_MODEL_IO [THE_MAIN_LOOP]',myThid)
256
257	C-- Save state for restarts
258	C Note: (jmc: is it still the case after ckp35 ?)
259	C =====
260	C Because of the ordering of the timestepping code and
261	C tendency term code at end of loop model arrays hold
262	C U,V,T,S at "time-level" N but gu, gv, gs, gt, guNM1,...
263	C at "time-level" N+1/2 (guNM1 at "time-level" N+1/2 is
264	C gu at "time-level" N-1/2) and etaN at "time-level" N+1/2.
265	C where N = I+timeLevBase-1
266	C Thus a checkpoint contains U.0000000000, GU.0000000001 and
267	C etaN.0000000001 in the indexing scheme used for the model
268	C "state" files. This example is referred to as a checkpoint
269	C at time level 1
270	CALL TIMER_START('WRITE_CHECKPOINT [THE_MAIN_LOOP]',myThid)
271	CALL WRITE_CHECKPOINT(
272	& .FALSE., myTime, myIter, myThid )
273	CALL TIMER_STOP ('WRITE_CHECKPOINT [THE_MAIN_LOOP]',myThid)
274
275	END