Improve efficiency of apply by the following: - Remove divisions in interior loop by storing and multiplying by the reciprocal of grid spacing instead. - Add @inline to apply(::Laplace - Remove initialization of w = 0 in apply(::Stencil) by manually unrolling first iteration of the loop.

# D2 order 4

boundary_stencils
     2    -5       4      -1     0     0
     1    -2       1       0     0     0
 -4/43 59/43 -110/43   59/43 -4/43     0
 -1/49     0   59/49 -118/49 64/49 -4/49

inner_stencil
-1/12     4/3  -5/2   4/3 -1/12

e
1

d1
-11/6 3 -3/2 1/3