...
Note that the overlap is 3 times larger on the left and right border than at the top and bottom of each of the two LAM grids! This is done because the solver needs the grids to be 3 times larger in x- than in y-direction (minus 1 point). An overlap is needed because the two LAM grids will give different answers in the overlap region and the larger the overlap region the easier it is for the solver to find the common solution.
...