--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SbpOperators/src/laplace/secondderivative.jl	Mon Jun 22 22:08:56 2020 +0200
@@ -0,0 +1,48 @@
+"""
+    SecondDerivative{T<:Real,N,M,K} <: TensorOperator{T,1}
+Implements the Laplace tensor operator `L` with constant grid spacing and coefficients
+in 1D dimension
+"""
+struct SecondDerivative{T<:Real,N,M,K} <: TensorOperator{T,1}
+    h_inv::T # The grid spacing could be included in the stencil already. Preferable?
+    innerStencil::Stencil{T,N}
+    closureStencils::NTuple{M,Stencil{T,K}}
+    parity::Parity
+    #TODO: Write a nice constructor
+end
+
+@enum Parity begin
+    odd = -1
+    even = 1
+end
+
+LazyTensors.domain_size(D2::SecondDerivative, range_size::NTuple{1,Integer}) = range_size
+
+function LazyTensors.apply(D2::SecondDerivative{T}, v::AbstractVector{T}, I::NTuple{1,Index}) where T
+    return apply(D2, v, I[1])
+end
+
+# Apply for different regions Lower/Interior/Upper or Unknown region
+@inline function LazyTensors.apply(D2::SecondDerivative, v::AbstractVector, i::Index{Lower})
+    return @inbounds D2.h_inv*D2.h_inv*apply_stencil(D2.closureStencils[Int(i)], v, Int(i))
+end
+
+@inline function LazyTensors.apply(D2::SecondDerivative, v::AbstractVector, i::Index{Interior})
+    return @inbounds D2.h_inv*D2.h_inv*apply_stencil(D2.innerStencil, v, Int(i))
+end
+
+@inline function LazyTensors.apply(D2::SecondDerivative, v::AbstractVector, i::Index{Upper})
+    N = length(v) # TODO: Use domain_size here instead?
+    return @inbounds D2.h_inv*D2.h_inv*Int(D2.parity)*apply_stencil_backwards(D2.closureStencils[N-Int(i)+1], v, Int(i))
+end
+
+@inline function LazyTensors.apply(D2::SecondDerivative, v::AbstractVector, index::Index{Unknown})
+    N = length(v)  # TODO: Use domain_size here instead?
+    r = getregion(Int(index), closuresize(L), N)
+    i = Index(Int(index), r)
+    return apply(D2, v, i)
+end
+
+function closuresize(D2::SecondDerivative{T<:Real,N,M,K}) where T,N,M,K
+    return M
+end