How the code for the Schwarz method implementation in LMDZ is organized

Schwarz loop (similar to NEMO)

The schwarz loop is implemented in the leapfrog_loc.F procedure that is responsible for the time stepping.

As with NEMO there are three loops around the original time-stepping scheme of leapfrog_loc.F:

• the outer loop increments counter iswloop with values : 1 to nsloops.
• the middle loop increments counter kswr with values : 1 to mswr.
• the inside loop increments counter itau with values : (iswloop - 1) * ntsinswr to iswloop * ntsinswr

As for NEMO if you run a 5 day simulation with a coupling window of 1 day and a Schwarz iteration number of 6. You get nsloops = 5 and mswr = 6. The value of ntsinswr depends on your time step. It is the number of dynamical time steps during a coupling window.

The loop is implemented around the time stepping scheme.

The beginning of the loops is before the 1 CONTINUE command:

c-----------------------------------
c  Beginning of schwarz looping
c-----------------------------------

      iswloop = 1

      swzloop: DO WHILE ( iswloop <= nsloops )

c$OMP MASTER
      IF (mpi_rank==0) THEN
         WRITE(lunout,*) 'leapfrog_loc'
         WRITE(lunout,*) '*** Schwarz loops ***'
         WRITE(lunout,*) 'iswloop = ',iswloop
      ENDIF
c$OMP END MASTER

      kswr = 1

      swzit: DO WHILE ( kswr <= mswr ) 

c$OMP MASTER
      IF (mpi_rank==0) THEN
         WRITE(lunout,*) 'kswr = ',kswr
      ENDIF
c$OMP END MASTER

      IF ( kswr == 1 ) THEN
        CALL store_current_time_swz
        CALL dynredem1_swz(vcov,ucov,teta,q,masse,ps,phis,p,pks,pk,pkf)
        swz_store = .TRUE.
      ELSE
        CALL restore_current_time_swz
        CALL dynetat0_swz(vcov,ucov,teta,q,masse,ps,phis,p,pks,pk,pkf)
        swz_restore = .TRUE.
      ENDIF

      itau = (iswloop - 1) * ntsinswr   

c-----------------------------------------------------------------------
c   Debut de l'integration temporelle:
c   ----------------------------------
c et du parallelisme !!

   1  CONTINUE ! Matsuno Forward step begins here

The end of the loops is after the test for MATSUNO/LEAPFROG vs PURE_MATSUNO method:

      END IF ! of IF(.not.purmats)

c------------------------------
cend of schwarz loop
c------------------------------

      END DO swzit! kswr

      iswloop = iswloop + 1

      END DO swzloop! iswloop

      call fin_swz_dyn ! deallocate schwarz dynamics pointers
      call fin_swz_phy ! deallocate schwarz physics arrays

a condition to cycle the loop on kswr is added inside the MATSUNO/LEAPFROG condition:

c-----------------------------------------
c Test de la fin de la fenêtre de Schwarz
c-----------------------------------------

            IF ( itau == iswloop * ntsinswr .AND.
     &         .NOT.(itau == itaufin .AND. kswr == mswr ) ) THEN
              kswr = kswr + 1
              CYCLE swzit
            ENDIF

c-----------------------------------------------------------------------
c   gestion de l'integration temporelle:
c   ------------------------------------

            IF( MOD(itau,iperiod).EQ.0 )    THEN
                    GO TO 1
            ELSE IF ( MOD(itau-1,iperiod). EQ. 0 ) THEN

It works only if the number of steps in the coupling windows is commensurate with the Matsuno steps frequency.

The loop needs to initialise the Schwarz parameters before starting:

c-------------------------------------
c Initialization of schwarz parameters
c-------------------------------------

      CALL init_swz_dyn ! allocate schwarz dynamics pointers
      CALL init_swz_phy ! allocate schwarz physics arrays

!      ncplfrq  = 86400
      ntsinswr = ncplfrq / dtvr
      nsloops  = itaufin / ntsinswr

c$OMP MASTER
      IF (mpi_rank==0) THEN
         WRITE(lunout,*) 'leapfrog_loc, ncplfrq  : ',ncplfrq
         WRITE(lunout,*) '              ntsinswr : ',ntsinswr
         WRITE(lunout,*) '              nsloops  : ',nsloops
         WRITE(lunout,*) '              mswr     : ',mswr
      ENDIF
c$OMP END MASTER

c-----------------------------------
c  Beginning of schwarz looping
c-----------------------------------

      iswloop = 1

coding details

coupling with OASIS

validation procedure