linerelax_periodicew.f90

subroutine linerelax(nxm,nym,nzm,cp,p,fn) 
!     -----------------------------------------                         
  USE header, only : NI,NJ,NK,rc_kind
!     This routine is called in place of relax from the multigrid solver
!     "mgrid".  It does not work (don't  know why).                     
!     call relax(nx(m),ny(m),nz(m),cp(loccp(m)),p(loco(m)),rhs(loci(m)))
!     solve  Grad p = fn                                                
      integer i,j,k,nxm,nym,nzm,info,im1,ip1,ii,istart,iseed 
      REAL(kind=rc_kind) :: p(0:nxm+1,0:nym+1,0:nzm+1),                      &
     &     fn(nxm,nym,nzm),cp(19,nxm,nym,nzm),subd(NK),supd(NK),        &
     &     dia(NK),rh(NK),dum,ran3                                      

iseed= 91294 
dum = ran3(iseed) 

do j=1,nym 
  istart = 0
  !istart=NI/2 
  do ii=1,nxm 
    i = ii + istart 
    if (i.gt.nxm) i = i -nxm 
    im1= i-1 
    ip1= i+1 
    if (i.eq.1) im1= nxm 
    if (i.eq.nxm) ip1= 1 
    do k=1,nzm 
       rh(k)= -( cp(2,i,j,k)*p(ip1,j,k)   &
       &   +cp(3,i,j,k)*p(i,j+1,k)        &
       &   +cp(4,i,j,k)*p(im1,j,k)        &
       &   +cp(5,i,j,k)*p(i,j-1,k)        &
       &   +cp(8,i,j,k)*p(im1,j+1,k)      &
       &   +cp(9,i,j,k)*p(im1,j-1,k)      &
       &   +cp(10,i,j,k)*p(ip1,j-1,k)     &
       &   +cp(11,i,j,k)*p(ip1,j+1,k)     &
       &   +cp(12,i,j,k)*p(im1,j,k-1)     &
       &   +cp(13,i,j,k)*p(ip1,j,k-1)     &
       &   +cp(14,i,j,k)*p(ip1,j,k+1)     &
       &   +cp(15,i,j,k)*p(im1,j,k+1)     &
       &   +cp(16,i,j,k)*p(i,j-1,k-1)     &
       &   +cp(17,i,j,k)*p(i,j+1,k-1)     &
       &   +cp(18,i,j,k)*p(i,j+1,k+1)     &
       &   +cp(19,i,j,k)*p(i,j-1,k+1)     &
       &   - fn(i,j,k) )                                       
       if (k.ne.1) subd(k)= cp(7,i,j,k) 
       if (k.ne.nzm) supd(k)= cp(6,i,j,k) 
       dia(k)= cp(1,i,j,k) 
     enddo 
     rh(1)= rh(1) -cp(7,i,j,1)*p(i,j,0) 
     rh(nzm)= rh(nzm) -cp(6,i,j,nzm)*p(i,j,nzm+1) 
     call dgtsl(nzm,subd,dia,supd,rh,info) 
     if (info.ne.0) then 
       write(6,*) 'error in linerelax' 
       stop 
     endif 
     p(i,j,1:nzm)= rh(1:nzm) 
   enddo
enddo 

return 
END