anchor.diff:  ! the following section solves the equation
   !     dti2*(km*u')'-u=-ub
   
  -      do j=1,jm
  -        do i=1,im
  -          dh(i,j)=1.d0
  -        end do
  -      end do
  +      dh = 1.
   
         do j=2,jm
           do i=2,im
  
positive.code: 
  ! initialize fields that are not calculated on all boundaries
  ! but are later used there
        do i=1,im
          do j=1,jm
            l0(i,j)=0.
           end do
        end do
        do i=1,im
          do j=1,jm
            do k=1,kb
              boygr(i,j,k)=0.
              prod(i,j,k)=0.
            end do
          end do
        end do
  
        do j=1,jmm1
          do i=1,imm1
  
negative.code:       end do
  
  ! calculate speed of sound squared
        cc = 0.
        do k=1,kbm1
          do j=1,jm
            do i=1,im
  