--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/volumeops/derivatives/second_derivative.jl	Sat Jul 17 18:07:15 2021 +0200
@@ -0,0 +1,20 @@
+"""
+    second_derivative(grid::EquidistantGrid{Dim}, inner_stencil, closure_stencils, direction)
+    second_derivative(grid::EquidistantGrid{1}, inner_stencil, closure_stencils)
+
+Creates the second-derivative operator `D2` as a `TensorMapping`
+
+`D2` approximates the second-derivative d²/dξ² on `grid` along the coordinate dimension specified by
+`direction`, using the stencil `inner_stencil` in the interior and a set of stencils `closure_stencils`
+for the points in the closure regions.
+
+On a one-dimensional `grid`, `D2` is a `VolumeOperator`. On a multi-dimensional `grid`, `D2` is the outer product of the
+one-dimensional operator with the `IdentityMapping`s in orthogonal coordinate dirrections.
+Also see the documentation of `SbpOperators.volume_operator(...)` for more details.
+"""
+function second_derivative(grid::EquidistantGrid{Dim}, inner_stencil, closure_stencils, direction) where Dim
+    h_inv = inverse_spacing(grid)[direction]
+    return SbpOperators.volume_operator(grid, scale(inner_stencil,h_inv^2), scale.(closure_stencils,h_inv^2), even, direction)
+end
+second_derivative(grid::EquidistantGrid{1}, inner_stencil, closure_stencils) = second_derivative(grid,inner_stencil,closure_stencils,1)
+export second_derivative