anchor.diff:                       shifty = (jj - refratio/2.d0 - 0.5d0)/refratio
   
                        value = qc + shiftx*gradx + shifty*grady
  -c                     i1 = ic
  -c                     j1 = jc
  -c                     qfine(i2,j2,mq) = value
   
                        ifine = ibc
                        jfine = (j-1)*refratio + jj
  
positive.code: 
                    if (iface_coarse .eq. 0) then
                       i1 = 1-ibc
                       i2 = j+jc_add
                    elseif (iface_coarse .eq. 1) then
                       i1 = mx+ibc
                       i2 = j+jc_add
                    endif
  
  c                 # Original code
  
negative.code: 
                    if (iface_coarse .eq. 2) then
                       i1 = i+ic_add
                       j1 = 1-jbc
                    elseif (iface_coarse .eq. 3) then
                       i1 = i+ic_add
                       j1 = my+jbc
                    endif
  
  c                 # Original code
  