--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/volumeops/derivatives/first_derivative.jl	Fri Feb 03 22:14:47 2023 +0100
@@ -0,0 +1,48 @@
+"""
+    first_derivative(grid::EquidistantGrid, inner_stencil, closure_stencils, direction)
+
+Creates the first-derivative operator `D1` as a `LazyTensor`
+
+`D1` approximates the first-derivative d/dξ 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`, `D1` is a `VolumeOperator`. On a multi-dimensional `grid`, `D1` is the inflation of
+a `VolumeOperator`.
+
+See also: [`VolumeOperator`](@ref), [`LazyTensors.inflate`](@ref).
+"""
+function first_derivative(grid::EquidistantGrid, inner_stencil, closure_stencils, direction)
+    h_inv = inverse_spacing(grid)[direction]
+
+    D₁ = VolumeOperator(restrict(grid, direction), scale(inner_stencil,h_inv), scale.(closure_stencils,h_inv), odd)
+    return LazyTensors.inflate(D₁, size(grid), direction)
+end
+
+
+"""
+    first_derivative(grid, inner_stencil, closure_stencils)
+
+Creates a `first_derivative` operator on a 1D `grid` given `inner_stencil` and `closure_stencils`.
+"""
+first_derivative(grid::EquidistantGrid{1}, inner_stencil::Stencil, closure_stencils) = first_derivative(grid, inner_stencil, closure_stencils, 1)
+
+
+"""
+    first_derivative(grid, stencil_set::StencilSet, direction)
+
+Creates a `first_derivative` operator on `grid` along coordinate dimension `direction` given a `stencil_set`.
+"""
+function first_derivative(grid::EquidistantGrid, stencil_set::StencilSet, direction)
+    inner_stencil = parse_stencil(stencil_set["D1"]["inner_stencil"])
+    closure_stencils = parse_stencil.(stencil_set["D1"]["closure_stencils"])
+    first_derivative(grid,inner_stencil,closure_stencils,direction);
+end
+
+
+"""
+    first_derivative(grid, stencil_set)
+
+Creates a `first_derivative` operator on a 1D `grid` given a `stencil_set`.
+"""
+first_derivative(grid::EquidistantGrid{1}, stencil_set::StencilSet) = first_derivative(grid, stencil_set, 1)