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 /*@@
   @file      sor.F
   @date      Thu Mar 13 07:46:55 1997
   @author    Joan Masso + Paul Walker
   @desc 
   The SOR solver
   @enddesc 
 @@*/

#include "cctk.h"
#include "cctk_arguments.h"
#include "cctk_parameters.h"


 /*@@
   @routine    sor
   @date       Thu Apr 24 13:29:52 1997
   @author     Joan Masso
   @desc 
      This is a standalone sor solver which does all the MPI itself.
      It is a pretty good example of doing pugh-based communications
      in FORTRAN.
   @enddesc 
@@*/

      subroutine sor_flat_core3d(_CCTK_FARGUMENTS,
     $   Mlinear_lsh,Mlinear,
     $   Nsource_lsh,Nsource,
     $   var,var_idx,
     $   abstol,reltol)

      implicit none

      _DECLARE_CCTK_FARGUMENTS
      DECLARE_CCTK_PARAMETERS
      INTEGER CCTK_Equals
      
      INTEGER Mlinear_lsh(3)
      CCTK_REAL Mlinear(Mlinear_lsh(1),Mlinear_lsh(2),Mlinear_lsh(3))

      INTEGER Nsource_lsh(3)
      CCTK_REAL Nsource(Nsource_lsh(1),Nsource_lsh(2),Nsource_lsh(3))

      CCTK_REAL var(cctk_lsh(1),cctk_lsh(2),cctk_lsh(3))
      INTEGER var_idx

      CCTK_REAL abstol(3),reltol(3)
      
      CCTK_REAL tol
      INTEGER toltype

      CCTK_REAL dx,dy,dz

c     Temporaries
      INTEGER sor_iteration
      CCTK_REAL tmp

c     Numbers...
      CCTK_REAL two, four

c     Total residual
      CCTK_REAL resnorm, residual

c     Stencil
      CCTK_REAL a(-1:1,-1:1,-1:1)

c     Loopers
      INTEGER i,j,k

c     Acceleration factor
      CCTK_REAL omega, rjacobian

c     conformal test
      logical conformal
      logical octant

c     Loop bounds. Starts, Ends, and deltas (steps)
      INTEGER is, js, ks, ie, je, ke, di, dj, dk, kstep

c     Coeeficients for the solver: 19 point stencil...  
      CCTK_REAL ac,ac_orig,aw,ae,an,as,at,ab
      CCTK_REAL ane,anw,ase,asw,ate,atw
      CCTK_REAL abe,abw,atn,ats,abn,asb

      CCTK_REAL finf
      CCTK_INT  npow

      logical cheb, const, none, verb
      integer Mlinear_storage,Nsource_storage
      INTEGER sum_handle,ierr

c     stencil size
      INTEGER sw(3)

      tol = AbsTol(1)

c     Get the reduction handel for the sum operation
      call CCTK_ReductionArrayHandle(sum_handle,"sum");
      if (sum_handle.lt.0) then 
        call CCTK_WARN(1,"Cannot get reduction handle.")
      endif

c     Set boundary related variables
      if (CCTK_EQUALS(sor_bound,"robin")) then
         sw(1)=1
         sw(2)=1
         sw(3)=1
         
         call Ell_GetRealKey(ierr, finf, "EllLinFlat::Bnd::Robin::inf")
         call Ell_GetIntKey (ierr, npow, "EllLinFlat::Bnd::Robin::falloff")
      end if
            
c     We have no storage for M/N if they are of size one in each direction
      if ((Mlinear_lsh(1).eq.1).and.(Mlinear_lsh(2).eq.1).and.(Mlinear_lsh(3).eq.1)) then
         Mlinear_storage=0
      else
         Mlinear_storage=1
      endif

      if ((Nsource_lsh(1).eq.1).and.(Nsource_lsh(2).eq.1).and.(Nsource_lsh(3).eq.1)) then
         Nsource_storage=0
      else
         Nsource_storage=1
      endif

c     Set up shorthand for the grid spacings
      dx=cctk_delta_space(1)
      dy=cctk_delta_space(2)
      dz=cctk_delta_space(3)


      verb   = CCTK_Equals(elliptic_verbose,"yes").eq.1
      octant = CCTK_Equals(domain,"octant").eq.1

c      cheb = contains("sor_accel","cheb").ne.0
c      const = contains("sor_accel","const").ne.0
c      none = contains("sor_accel","none").ne.0

      verb = .true.
      cheb = .false.
      none = .false.
      const = .false.

      if (verb .and. cheb) 
     $     print *,"Chebyshev Acceleration with radius of 1"
      if (verb .and. const)
     $     print *,"SOR with omega = 1.8"
      if (verb .and. none)
     $     print *,"Un-accelearted relaxation (omega = 1)"

      two     = 2.0D0
      four    = 4.0D0
      resnorm = 0
      
      ae = 1.0d0/dx**2.
      aw = 1.0d0/dx**2.
      an = 1.0d0/dy**2.
      as = 1.0d0/dy**2.
      at = 1.0d0/dz**2.
      ab = 1.0d0/dz**2.
      ac_orig = -2.0d0/dx**2. - 2.0d0/dy**2. - 2.0d0/dz**2.

      do sor_iteration=1,maxit

c     We do not know the spectral radius of the Jacobi iteration, 
c     so we will take it to be one which empirically seems to be pretty good 
         rjacobian = 1.0D0

c     Set up the omega factor
         omega = 1.0D0
         if (cheb) then 
            do i=2,sor_iteration
               omega = 1.0D0/(1.0D0 - .25D0*rjacobian**2*omega)
            enddo
         endif
         if (const) then 
            omega = 1.8
         endif
         
c     Total norm of the residual zero
         resnorm = 0.
         
c     Start loop with Red Black
         ks = mod(sor_iteration,2)+2
         
         if (cctk_lsh(3) .eq. 3) then
            ks = 2
         endif
         kstep = 2

         do k=ks,cctk_lsh(3)-1,kstep
            do j=2,cctk_lsh(2)-1
               do i=2,cctk_lsh(1)-1

                  ac = ac_orig                  
             
                  if (Mlinear_storage.eq.1) then
                     ac = ac - Mlinear(i,j,k)
                  endif

                  residual = ac*var(i,j,k) 
     &                 + ae*var(i+1,j,k) + aw*var(i-1,j,k)
     &                 + an*var(i,j+1,k) + as*var(i,j-1,k)
     &                 + at*var(i,j,k+1) + ab*var(i,j,k-1)

                  if (Nsource_storage.eq.1) then
                     residual = residual - Nsource(i,j,k)
                  endif
                  
c     Accumulate to the total Norm of the residual
                  resnorm = resnorm + abs(residual)
c     Update
                  var(i,j,k) = var(i,j,k) - omega*residual/ac
               end do
            end do
         end do   

c     Reduce the norm
         call CCTK_ReduceLocalScalar(ierr, cctkGH, -1, sum_handle, 
     $        resnorm, residual, CCTK_VARIABLE_REAL) 
         if (ierr.ne.0) then
            call CCTK_WARN(1,"Reduction of norm failed!");
         endif

         residual = residual / (cctk_gsh(1)*cctk_gsh(2)*cctk_gsh(3))

c         write (*,*) "Iteration/Norm",sor_iteration,residual

c     Synchronize the variables
         call CCTK_SyncGroupWithVarI(cctkGH, var_idx)
         
         if (residual .lt. tol) then 
            goto 123
         endif

c     Apply boundary conditions
c         call Ell_GetStringKey(nchar, mybound,"EllLinFlat::Bnd")

         if (CCTK_EQUALS(sor_bound,"robin")) then
            call RobinBCVarI(ierr, cctkGH, finf, npow, sw, var_idx);
            if (ierr.ne.0) then
               call CCTK_WARN(1,"Could not apply Robin BC !")
            endif
         endif

c     Apply octant Symmetries         
         call CartSymBCVarI(ierr, cctkGH, var_idx)

      enddo

      write (*,*) "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
      write (*,*) "!! WARNING: SOR SOLVER DID NOT CONVERGE  !!"
      write (*,*) "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"

 123  continue

      if (verb) write (*,*) "Iteration/Norm",sor_iteration,residual

      return
      end