--- a/src/SbpOperators/boundaryops/boundary_operator.jl	Mon May 23 07:20:27 2022 +0200
+++ b/src/SbpOperators/boundaryops/boundary_operator.jl	Tue Feb 10 22:41:19 2026 +0100
@@ -1,80 +1,52 @@
 """
-    boundary_operator(grid,closure_stencil,boundary)
-
-Creates a boundary operator on a `Dim`-dimensional grid for the
-specified `boundary`. The action of the operator is determined by `closure_stencil`.
-
-When `Dim=1`, the corresponding `BoundaryOperator` tensor mapping is returned.
-When `Dim>1`, the `BoundaryOperator` `op` is inflated by the outer product
-of `IdentityTensors` in orthogonal coordinate directions, e.g for `Dim=3`,
-the boundary restriction operator in the y-direction direction is `Ix⊗op⊗Iz`.
-"""
-function boundary_operator(grid::EquidistantGrid, closure_stencil, boundary::CartesianBoundary)
-    #TODO:Check that dim(boundary) <= Dim?
-
-    # Create 1D boundary operator
-    r = region(boundary)
-    d = dim(boundary)
-    op = BoundaryOperator(restrict(grid, d), closure_stencil, r)
-
-    # Create 1D IdentityTensors for each coordinate direction
-    one_d_grids = restrict.(Ref(grid), Tuple(1:dimension(grid)))
-    Is = IdentityTensor{eltype(grid)}.(size.(one_d_grids))
-
-    # Formulate the correct outer product sequence of the identity mappings and
-    # the boundary operator
-    parts = Base.setindex(Is, op, d)
-    return foldl(⊗, parts)
-end
-
-"""
-    BoundaryOperator{T,R,N} <: LazyTensor{T,0,1}
+    BoundaryOperator{T,B,N} <: LazyTensor{T,0,1}
 
 Implements the boundary operator `op` for 1D as a `LazyTensor`
 
-`op` is the restriction of a grid function to the boundary using some closure `Stencil{T,N}`.
-The boundary to restrict to is determined by `R`.
-`op'` is the prolongation of a zero dimensional array to the whole grid using the same closure stencil.
+`op` is the restriction of a grid function to the boundary using some closure
+`Stencil{T,N}`. The boundary to restrict to is determined by `B`. `op'` is the
+prolongation of a zero dimensional array to the whole grid using the same
+closure stencil.
 """
-struct BoundaryOperator{T,R<:Region,N} <: LazyTensor{T,0,1}
+struct BoundaryOperator{T,B<:BoundaryIdentifier,N} <: LazyTensor{T,0,1}
     stencil::Stencil{T,N}
     size::Int
 end
 
-BoundaryOperator{R}(stencil::Stencil{T,N}, size::Int) where {T,R,N} = BoundaryOperator{T,R,N}(stencil, size)
-
 """
-    BoundaryOperator(grid::EquidistantGrid{1}, closure_stencil, region)
+    BoundaryOperator(grid::EquidistantGrid, closure_stencil, boundary)
 
-Constructs the BoundaryOperator with stencil `closure_stencil` for a one-dimensional `grid`, restricting to
-to the boundary specified by `region`.
+Constructs the BoundaryOperator with stencil `closure_stencil` for a
+`EquidistantGrid` `grid`, restricting to to the boundary specified by
+`boundary`.
 """
-function BoundaryOperator(grid::EquidistantGrid{1}, closure_stencil::Stencil{T,N}, region::Region) where {T,N}
-    return BoundaryOperator{T,typeof(region),N}(closure_stencil,size(grid)[1])
+function BoundaryOperator(grid::EquidistantGrid, closure_stencil::Stencil{T,N}, boundary::BoundaryIdentifier) where {T,N}
+    return BoundaryOperator{T,typeof(boundary),N}(closure_stencil,size(grid)[1])
 end
 
 """
     closure_size(::BoundaryOperator)
+
 The size of the closure stencil.
 """
-closure_size(::BoundaryOperator{T,R,N}) where {T,R,N} = N
+closure_size(::BoundaryOperator{T,B,N}) where {T,B,N} = N
 
 LazyTensors.range_size(op::BoundaryOperator) = ()
 LazyTensors.domain_size(op::BoundaryOperator) = (op.size,)
 
-function LazyTensors.apply(op::BoundaryOperator{<:Any,Lower}, v::AbstractVector)
+function LazyTensors.apply(op::BoundaryOperator{<:Any,LowerBoundary}, v::AbstractVector)
     apply_stencil(op.stencil,v,1)
 end
 
-function LazyTensors.apply(op::BoundaryOperator{<:Any,Upper}, v::AbstractVector)
+function LazyTensors.apply(op::BoundaryOperator{<:Any,UpperBoundary}, v::AbstractVector)
     apply_stencil_backwards(op.stencil,v,op.size)
 end
 
-function LazyTensors.apply_transpose(op::BoundaryOperator{<:Any,Lower}, v::AbstractArray{<:Any,0}, i::Index{Lower})
+function LazyTensors.apply_transpose(op::BoundaryOperator{<:Any,LowerBoundary}, v::AbstractArray{<:Any,0}, i::Index{Lower})
     return op.stencil[Int(i)-1]*v[]
 end
 
-function LazyTensors.apply_transpose(op::BoundaryOperator{<:Any,Upper}, v::AbstractArray{<:Any,0}, i::Index{Upper})
+function LazyTensors.apply_transpose(op::BoundaryOperator{<:Any,UpperBoundary}, v::AbstractArray{<:Any,0}, i::Index{Upper})
     return op.stencil[op.size[1] - Int(i)]*v[]
 end