--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SbpOperators/src/constantlaplace.jl	Mon Jun 22 19:47:20 2020 +0200
@@ -0,0 +1,53 @@
+#TODO: Naming?! What is this? It is a 1D tensor operator but what is then the
+# potentially multi-D laplace tensor mapping then?
+# Ideally I would like the below to be the laplace operator in 1D, while the
+# multi-D operator is a a tuple of the 1D-operator. Possible via recursive
+# definitions? Or just bad design?
+"""
+    ConstantLaplaceOperator{T<:Real,N,M,K} <: TensorOperator{T,1}
+Implements the Laplace tensor operator `L` with constant grid spacing and coefficients
+in 1D dimension
+"""
+struct ConstantLaplaceOperator{T<:Real,N,M,K} <: TensorOperator{T,1}
+    h_inv::T # The grid spacing could be included in the stencil already. Preferable?
+    a::T # TODO: Better name?
+    innerStencil::Stencil{T,N}
+    closureStencils::NTuple{M,Stencil{T,K}}
+    parity::Parity
+end
+
+@enum Parity begin
+    odd = -1
+    even = 1
+end
+
+LazyTensors.domain_size(L::ConstantLaplaceOperator, range_size::NTuple{1,Integer}) = range_size
+
+function LazyTensors.apply(L::ConstantLaplaceOperator{T}, v::AbstractVector{T}, I::NTuple{1,Index}) where T
+    return L.a*apply_2nd_derivative(L, L.h_inv, v, I[1])
+end
+
+# Apply for different regions Lower/Interior/Upper or Unknown region
+@inline function apply_2nd_derivative(L::ConstantLaplaceOperator, h_inv::Real, v::AbstractVector, i::Index{Lower})
+    return @inbounds h_inv*h_inv*apply_stencil(L.closureStencils[Int(i)], v, Int(i))
+end
+
+@inline function apply_2nd_derivative(L::ConstantLaplaceOperator, h_inv::Real, v::AbstractVector, i::Index{Interior})
+    return @inbounds h_inv*h_inv*apply_stencil(L.innerStencil, v, Int(i))
+end
+
+@inline function apply_2nd_derivative(L::ConstantLaplaceOperator, h_inv::Real, v::AbstractVector, i::Index{Upper})
+    N = length(v) # Can we use range_size here instead?
+    return @inbounds h_inv*h_inv*Int(L.parity)*apply_stencil_backwards(L.closureStencils[N-Int(i)+1], v, Int(i))
+end
+
+@inline function apply_2nd_derivative(L::ConstantLaplaceOperator, h_inv::Real, v::AbstractVector, index::Index{Unknown})
+    N = length(v) # Can we use range_size here instead?
+    r = getregion(Int(index), closuresize(L), N)
+    i = Index(Int(index), r)
+    return apply_2nd_derivative(op, h_inv, v, i)
+end
+
+function closuresize(L::ConstantLaplaceOperator{T<:Real,N,M,K})::Int
+    return M
+end