function out = my_laplacian(in)
  out = -in ...
      + .20*(circshift(in,[ 1, 0]) + circshift(in,[-1, 0])  ...
      +      circshift(in,[ 0, 1]) + circshift(in,[ 0,-1])) ...
      + .05*(circshift(in,[ 1, 1]) + circshift(in,[-1, 1])  ...
      +      circshift(in,[-1,-1]) + circshift(in,[ 1,-1]));
