anchor.diff:      open(unit=10, form='unformatted', file=name)
       read(10) array_small
       close(10)
  -
       array(1:nx+1, 1:ny, :) = array_small
  -    ! wrap array around for periodicity
  -    array(0, :, :) = array(nx, :, :)
  -    array(nx+1, :, :) = array(1, :, :)
  -    array(:, 0, :) = array(:, ny, :)
  -    array(:, ny+1, :) = array(:, 1, :)
  +    call wrap_fields_3D(array, nx, ny, layers)
     else
       array = default
     end if
  
positive.code:     open(unit=10, form='unformatted', file=name)
      read(10) array_small
      close(10)
  
      array(1:nx, 1:ny) = array_small
      ! wrap array around for periodicity
      array(0, :) = array(nx, :)
      array(nx+1, :) = array(1, :)
      array(:, 0) = array(:, ny)
      array(:, ny+1) = array(:, 1)
    else
      array = default
    end if
  
negative.code:     open(unit=10, form='unformatted', file=name)
      read(10) array_small
      close(10)
      array(1:nx, 1:ny, :) = array_small
      call wrap_fields_3D(array, nx, ny, layers)
    else
      do k = 1, layers
        array(:, :, k) = default(k)
  