anchor.diff:          do i = ilo-1, ihi+1
   
              ! limit? MC Eq. 24 and 25
  -           if (dafm(i,j) * dafp(i,j) <= 0.0 .or. &
  -                (a(i,j) - a(i-2,j))*(a(i+2,j) - a(i,j)) <= 0.0) then
  +           if (dafm(i,j) * dafp(i,j) <= 0.0d0 .or. &
  +                (a(i,j) - a(i-2,j))*(a(i+2,j) - a(i,j)) <= 0.0d0) then
   
                 ! we are at an extrema
   
  
positive.code:                        ! Eqs. 29, 30
                         ar(i,j) = a(i,j) - rho*dafm(i,j)  ! note: typo in Eq 29
                         al(i,j+1) = a(i,j) + rho*dafp(i,j)
                      else if (abs(dafm(i,j)) >= 2.0*abs(dafp(i,j))) then
                         ! Eq. 31
                         ar(i,j) = a(i,j) - 2.0d0*(1.0d0 - rho)*dafp(i,j) - rho*dafm(i,j)
                      else if (abs(dafp(i,j)) >= 2.0*abs(dafm(i,j))) then
  
negative.code:            dafp(i,j) = a_int(i+1,j) - a(i,j)
  
             ! these live on cell-centers
             d2af(i,j) = 6.0d0*(a_int(i,j) - 2.0d0*a(i,j) + a_int(i+1,j))
          enddo
       enddo
  
       do j = jlo-1, jhi+1
          do i = ilo-3, ihi+3
             d2ac(i,j) = a(i-1,j) - 2.0d0*a(i,j) + a(i+1,j)
          enddo
       enddo
  
  