changeset 1091:e3b41d48b5aa feature/variable_derivatives

Merge refactor/grids
author Jonatan Werpers <jonatan@werpers.com>
date Tue, 26 Apr 2022 14:29:08 +0200
parents de972d825289 (diff) 9b40aeac4269 (current diff)
children 703eaa3e50c4
files
diffstat 21 files changed, 1149 insertions(+), 26 deletions(-) [+]
line wrap: on
line diff
--- a/src/LazyTensors/lazy_tensor_operations.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/LazyTensors/lazy_tensor_operations.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -1,3 +1,5 @@
+using Sbplib.RegionIndices
+
 """
     TensorApplication{T,R,D} <: LazyArray{T,R}
 
@@ -268,6 +270,20 @@
 LazyOuterProduct(tms::Vararg{LazyTensor}) = foldl(LazyOuterProduct, tms)
 
 
+
+"""
+    inflate(tm, sz, dir)
+
+Inflate `tm` with identity tensors in all directions `d` for `d != dir`.
+
+# TODO: Describe when it is useful
+"""
+function inflate(tm::LazyTensor, sz, dir)
+    Is = IdentityTensor{eltype(tm)}.(sz)
+    parts = Base.setindex(Is, tm, dir)
+    return foldl(⊗, parts)
+end
+
 function check_domain_size(tm::LazyTensor, sz)
     if domain_size(tm) != sz
         throw(DomainSizeMismatch(tm,sz))
@@ -290,7 +306,6 @@
     print(io, "domain size $(domain_size(err.tm)) of LazyTensor not matching size $(err.sz)")
 end
 
-
 struct RangeSizeMismatch <: Exception
     tm::LazyTensor
     sz
@@ -300,3 +315,29 @@
     print(io, "RangeSizeMismatch: ")
     print(io, "range size $(range_size(err.tm)) of LazyTensor not matching size $(err.sz)")
 end
+
+
+function apply_with_region(op, v, boundary_width::Integer, dim_size::Integer, i)
+    if 0 < i <= boundary_width
+        return LazyTensors.apply(op,v,Index(i,Lower))
+    elseif boundary_width < i <= dim_size-boundary_width
+        return LazyTensors.apply(op,v,Index(i,Interior))
+    elseif dim_size-boundary_width < i <= dim_size
+        return LazyTensors.apply(op,v,Index(i,Upper))
+    else
+        error("Bounds error") # TODO: Make this more standard
+    end
+end
+# TBD: Can these methods be merge by having a function as an arguement instead?
+# TODO: Add inference test that show where things break and how this rewrite fixes it.
+function apply_transpose_with_region(op, v, boundary_width::Integer, dim_size::Integer, i)
+    if 0 < i <= boundary_width
+        return LazyTensors.apply_transpose(op,v,Index(i,Lower))
+    elseif boundary_width < i <= dim_size-boundary_width
+        return LazyTensors.apply_transpose(op,v,Index(i,Interior))
+    elseif dim_size-boundary_width < i <= dim_size
+        return LazyTensors.apply_transpose(op,v,Index(i,Upper))
+    else
+        error("Bounds error") # TODO: Make this more standard
+    end
+end
\ No newline at end of file
--- a/src/LazyTensors/tuple_manipulation.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/LazyTensors/tuple_manipulation.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -74,3 +74,23 @@
 flatten_tuple(t::NTuple{N, Number} where N) = t
 flatten_tuple(t::Tuple) = ((flatten_tuple.(t)...)...,) # simplify?
 flatten_tuple(ts::Vararg) = flatten_tuple(ts)
+
+
+function left_pad_tuple(t, val, N)
+    if N < length(t)
+        throw(DomainError(N, "Can't pad tuple of length $(length(t)) to $N elements"))
+    end
+
+    padding = ntuple(i->val, N-length(t))
+    return (padding..., t...)
+end
+
+function right_pad_tuple(t, val, N)
+    if N < length(t)
+        throw(DomainError(N, "Can't pad tuple of length $(length(t)) to $N elements"))
+    end
+
+    padding = ntuple(i->val, N-length(t))
+    return (t..., padding...)
+end
+
--- a/src/RegionIndices/RegionIndices.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/RegionIndices/RegionIndices.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -65,6 +65,7 @@
         error("Bounds error") # TODO: Make this more standard
     end
 end
+# 2022-02-21: Using the return values of getregion cause type inference to give up in certain cases, for example H*H*v
 
 export getregion
 
--- a/src/SbpOperators/SbpOperators.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/SbpOperators.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -5,6 +5,7 @@
 export read_stencil_set
 export get_stencil_set
 export parse_stencil
+export parse_nested_stencil
 export parse_scalar
 export parse_tuple
 export sbp_operators_path
@@ -19,6 +20,7 @@
 export normal_derivative
 export first_derivative
 export second_derivative
+export undivided_dissipation
 
 using Sbplib.RegionIndices
 using Sbplib.LazyTensors
@@ -29,12 +31,17 @@
     even = 1
 end
 
+export closure_size
+
 include("stencil.jl")
 include("stencil_set.jl")
 include("volumeops/volume_operator.jl")
+include("volumeops/stencil_operator_distinct_closures.jl")
 include("volumeops/constant_interior_scaling_operator.jl")
 include("volumeops/derivatives/first_derivative.jl")
 include("volumeops/derivatives/second_derivative.jl")
+include("volumeops/derivatives/second_derivative_variable.jl")
+include("volumeops/derivatives/dissipation.jl")
 include("volumeops/laplace/laplace.jl")
 include("volumeops/inner_products/inner_product.jl")
 include("volumeops/inner_products/inverse_inner_product.jl")
--- a/src/SbpOperators/boundaryops/boundary_operator.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/boundaryops/boundary_operator.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -12,19 +12,14 @@
 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)
+    op = BoundaryOperator(restrict(grid, d), closure_stencil, region(boundary))
 
     # 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)
+    return LazyTensors.inflate(op, size(grid), d)
 end
 
 """
@@ -84,6 +79,5 @@
 end
 
 function LazyTensors.apply_transpose(op::BoundaryOperator, v::AbstractArray{<:Any,0}, i)
-    r = getregion(i, closure_size(op), op.size)
-    apply_transpose(op, v, Index(i,r))
+    return LazyTensors.apply_transpose_with_region(op, v, closure_size(op), op.size[1], i)
 end
--- a/src/SbpOperators/operators/standard_diagonal.toml	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/operators/standard_diagonal.toml	Tue Apr 26 14:29:08 2022 +0200
@@ -20,6 +20,10 @@
 H.inner = "1"
 H.closure = ["1/2"]
 
+e.closure = ["1"]
+d1.closure = {s = ["3/2", "-2", "1/2"], c = 1}
+
+
 D1.inner_stencil = ["-1/2", "0", "1/2"]
 D1.closure_stencils = [
     {s = ["-1", "1"], c = 1},
@@ -30,8 +34,10 @@
     {s = ["1", "-2", "1"], c = 1},
 ]
 
-e.closure = ["1"]
-d1.closure = {s = ["3/2", "-2", "1/2"], c = 1}
+D2variable.inner_stencil = [["1/2", "1/2", "0"],[ "-1/2", "-1", "-1/2"],["0", "1/2", "1/2"]]
+D2variable.closure_stencils = [
+        {s = [["2", "-1", "0"],["-3", "1",   "0"],["1","0","0"]], c = 1},
+]
 
 [[stencil_set]]
 
@@ -40,6 +46,9 @@
 H.inner = "1"
 H.closure = ["17/48", "59/48", "43/48", "49/48"]
 
+e.closure = ["1"]
+d1.closure = {s = ["11/6", "-3", "3/2", "-1/3"], c = 1}
+
 D1.inner_stencil = ["1/12","-2/3","0","2/3","-1/12"]
 D1.closure_stencils = [
     {s = [ "-24/17",  "59/34",  "-4/17", "-3/34",     "0",     "0"], c = 1},
@@ -56,5 +65,79 @@
     {s = [ "-1/49",     "0",   "59/49", "-118/49", "64/49", "-4/49"], c = 4},
 ]
 
+D2variable.inner_stencil = [
+    ["-1/8",   "1/6", "-1/8",   "0",    "0"  ],
+    [ "1/6",   "1/2",  "1/2",  "1/6",   "0"  ],
+    ["-1/24", "-5/6", "-3/4", "-5/6", "-1/24"],
+    [  "0",    "1/6",  "1/2",  "1/2",  "1/6" ],
+    [  "0",     "0",  "-1/8",  "1/6", "-1/8" ],
+]
+D2variable.closure_stencils = [
+    {c = 1, s = [
+        [  "920/289",  "-59/68",              "-81031200387/366633756146",                  "-69462376031/733267512292",              "0",             "0",      "0",     "0"  ],
+        ["-1740/289",     "0",                  "6025413881/7482321554",                      "1612249989/7482321554",                "0",             "0",      "0",     "0"  ],
+        [ "1128/289",   "59/68",               "-6251815797/8526366422",                      "-639954015/17052732844",               "0",             "0",      "0",     "0"  ],
+        [ "-308/289",     "0",                  "1244724001/7482321554",                      "-752806667/7482321554",                "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",                  "-148737261/10783345769",                      "148737261/10783345769",               "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",                          "-3/833",                                      "3/833",                       "0",             "0",      "0",     "0"  ],
+    ]},
+    {c = 2, s = [
+        [   "12/17",      "0",                   "102125659/440136562",                         "27326271/440136562",                 "0",             "0",      "0",     "0"  ],
+        [  "-59/68",      "0",            "-156920047993625/159775733917868",            "-12001237118451/79887866958934",            "0",             "0",      "0",     "0"  ],
+        [    "2/17",      "0",               "1489556735319/1857857371138",                 "149729180391/1857857371138",             "0",             "0",      "0",     "0"  ],
+        [    "3/68",      "0",             "-13235456910147/159775733917868",              "3093263736297/79887866958934",            "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",                 "67535018271/2349643145851",                 "-67535018271/2349643145851",             "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",                         "441/181507",                                "-441/181507",                    "0",             "0",      "0",     "0"  ],
+    ]},
+    {c = 3, s = [
+        [  "-96/731",   "59/172",              "-6251815797/21566691538",                     "-639954015/43133383076",               "0",             "0",      "0",     "0"  ],
+        [  "118/731",     "0",              "87883847383821/79887866958934",               "8834021643069/79887866958934",            "0",             "0",      "0",     "0"  ],
+        [  "-16/731",  "-59/172",  "-1134866646907639536627/727679167377258785038",   "-13777050223300597/23487032885926596",   "-26254/557679",       "0",      "0",     "0"  ],
+        [   "-6/731",     "0",        "14509020271326561681/14850595252597118062",        "17220493277981/79887866958934",     "1500708/7993399",      "0",      "0",     "0"  ],
+        [     "0",        "0",        "-4841930283098652915/21402328452272317207",        "31597236232005/115132514146699",     "-26254/185893",       "0",      "0",     "0"  ],
+        [     "0",        "0",                 "-2318724711/1653303156799",                       "960119/1147305747",           "13564/23980197",     "0",      "0",     "0"  ],
+    ]},
+    {c = 4, s = [
+        [  "-36/833",     "0",                  "1244724001/21566691538",                    "-752806667/21566691538",                "0",             "0",      "0",     "0"  ],
+        [  "177/3332",    "0",            "-780891957698673/7829010961975532",            "3724542049827/79887866958934",             "0",             "0",      "0",     "0"  ],
+        [   "-6/833",     "0",        "14509020271326561681/16922771334354855466",        "2460070468283/13005001597966",      "1500708/9108757",      "0",      "0",     "0"  ],
+        [   "-9/3332",    "0",      "-217407431400324796377/207908333536359652868",   "-1950062198436997/3914505480987766",   "-7476412/9108757",    "-2/49",    "0",     "0"  ],
+        [     "0",        "0",         "4959271814984644613/21402328452272317207",       "47996144728947/115132514146699",     "4502124/9108757",     "8/49",    "0",     "0"  ],
+        [     "0",        "0",                 "-2258420001/1653303156799",                    "-1063649/8893843",             "1473580/9108757",    "-6/49",    "0",     "0"  ],
+    ]},
+    {c = 5, s = [
+        [     "0",        "0",                   "-49579087/10149031312",                       "49579087/10149031312",               "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",               "1328188692663/37594290333616",              "-1328188692663/37594290333616",            "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",        "-1613976761032884305/7963657098519931984",         "10532412077335/42840005263888",     "-564461/4461432",      "0",      "0",     "0"  ],
+        [     "0",        "0",         "4959271814984644613/20965546238960637264",        "15998714909649/37594290333616",      "375177/743572",      "1/6",     "0",     "0"  ],
+        [     "0",        "0",        "-8386761355510099813/128413970713633903242",    "-2224717261773437/2763180339520776",   "-280535/371786",     "-5/6",   "-1/24",   "0"  ],
+        [     "0",        "0",                 "13091810925/13226425254392",                    "35039615/213452232",          "1118749/2230716",     "1/2",    "1/6",    "0"  ],
+        [     "0",        "0",                            "0",                                          "0",                        "-1/8",           "1/6",   "-1/8",    "0"  ],
+    ]},
+    {c = 6, s = [
+        [     "0",        "0",                          "-1/784",                                      "1/784",                       "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",                        "8673/2904112",                              "-8673/2904112",                   "0",             "0",      "0",     "0"  ],
+        [     "0",        "0",                "-33235054191/26452850508784",                      "960119/1280713392",            "3391/6692148",      "0",      "0",     "0"  ],
+        [     "0",        "0",                  "-752806667/539854092016",                      "-1063649/8712336",             "368395/2230716",    "-1/8",     "0",     "0"  ],
+        [     "0",        "0",                 "13091810925/13226425254392",                    "35039615/213452232",          "1118749/2230716",     "1/2",    "1/6",    "0"  ],
+        [     "0",        "0",                  "-660204843/13226425254392",                    "-3290636/80044587",          "-5580181/6692148",    "-3/4",   "-5/6",  "-1/24"],
+        [     "0",        "0",                            "0",                                          "0",                         "1/6",           "1/2",    "1/2",   "1/6" ],
+        [     "0",        "0",                            "0",                                          "0",                          "0",           "-1/8",    "1/6",  "-1/8" ],
+    ]}
+]
+
+
+
+[[stencil_set]]
+
+order = 6
+
+H.inner = "1"
+H.closure = ["13649/43200", "12013/8640", "2711/4320", "5359/4320", "7877/8640", "43801/43200"]
+
+
+
+
+
 e.closure = ["1"]
-d1.closure = {s = ["11/6", "-3", "3/2", "-1/3"], c = 1}
+d1.closure = ["-25/12", "4", "-3", "4/3", "-1/4"]
--- a/src/SbpOperators/stencil.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/stencil.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -85,6 +85,21 @@
     return w
 end
 
+function left_pad(s::Stencil, N)
+    weights = LazyTensors.left_pad_tuple(s.weights, zero(eltype(s)), N)
+    range = (first(s.range) - (N - length(s.weights))):last(s.range)
+
+    return Stencil(range, weights)
+end
+
+function right_pad(s::Stencil, N)
+    weights = LazyTensors.right_pad_tuple(s.weights, zero(eltype(s)), N)
+    range = first(s.range):(last(s.range) + (N - length(s.weights)))
+
+    return Stencil(range, weights)
+end
+
+
 
 struct NestedStencil{T,N,M}
     s::Stencil{Stencil{T,N},M}
--- a/src/SbpOperators/stencil_set.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/stencil_set.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -110,6 +110,33 @@
     end
 end
 
+
+"""
+    parse_nested_stencil(parsed_toml)
+
+Accept parsed TOML and read it as a nested tuple.
+
+See also [`read_stencil_set`](@ref), [`parse_stencil`](@ref).
+"""
+function parse_nested_stencil(parsed_toml)
+    if parsed_toml isa Array
+        weights = parse_stencil.(parsed_toml)
+        return CenteredNestedStencil(weights...)
+    end
+
+    center = parsed_toml["c"]
+    weights = parse_tuple.(parsed_toml["s"])
+    return NestedStencil(weights...; center)
+end
+
+"""
+    parse_nested_stencil(T, parsed_toml)
+
+Parse the input as a nested stencil with element type `T`.
+"""
+parse_nested_stencil(T, parsed_toml) = NestedStencil{T}(parse_nested_stencil(parsed_toml))
+
+
 """
     parse_scalar(parsed_toml)
 
--- a/src/SbpOperators/volumeops/constant_interior_scaling_operator.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/volumeops/constant_interior_scaling_operator.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -41,8 +41,7 @@
 end
 
 function LazyTensors.apply(op::ConstantInteriorScalingOperator, v::AbstractVector, i)
-    r = getregion(i, closure_size(op), op.size[1])
-    return LazyTensors.apply(op, v, Index(i, r))
+    return LazyTensors.apply_with_region(op, v, closure_size(op), op.size[1], i)
 end
 
 LazyTensors.apply_transpose(op::ConstantInteriorScalingOperator, v, i) = apply(op, v, i)
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/volumeops/derivatives/dissipation.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,87 @@
+function undivided_dissipation(g::EquidistantGrid, p, direction)
+    T = eltype(g)
+    interior_weights = T.(dissipation_interior_weights(p))
+
+    D  = stencil_operator_distinct_closures(
+        g,
+        dissipation_interior_stencil(interior_weights),
+        dissipation_lower_closure_stencils(interior_weights),
+        dissipation_upper_closure_stencils(interior_weights),
+        direction,
+    )
+    Dᵀ = stencil_operator_distinct_closures(
+        g,
+        dissipation_transpose_interior_stencil(interior_weights),
+        dissipation_transpose_lower_closure_stencils(interior_weights),
+        dissipation_transpose_upper_closure_stencils(interior_weights),
+        direction,
+    )
+
+    return D, Dᵀ
+end
+
+undivided_dissipation(g::EquidistantGrid{1}, p) = undivided_dissipation(g, p, 1)
+
+function dissipation_interior_weights(p)
+   if p == 0
+       return (1,)
+   end
+
+   return (0, dissipation_interior_weights(p-1)...) .- (dissipation_interior_weights(p-1)..., 0)
+end
+
+midpoint(weights) = length(weights)÷2 + 1
+midpoint_transpose(weights) = length(weights)+1 - midpoint(weights)
+
+function dissipation_interior_stencil(weights)
+    return Stencil(weights..., center=midpoint(weights))
+end
+function dissipation_transpose_interior_stencil(weights)
+    if iseven(length(weights))
+        weights = map(-, weights)
+    end
+
+    return Stencil(weights..., center=midpoint_transpose(weights))
+end
+
+dissipation_lower_closure_size(weights) = midpoint(weights) - 1
+dissipation_upper_closure_size(weights) = length(weights) - midpoint(weights)
+
+dissipation_lower_closure_stencils(interior_weights) = ntuple(i->Stencil(interior_weights..., center=i                       ), dissipation_lower_closure_size(interior_weights))
+dissipation_upper_closure_stencils(interior_weights) = ntuple(i->Stencil(interior_weights..., center=length(interior_weights)-dissipation_upper_closure_size(interior_weights)+i), dissipation_upper_closure_size(interior_weights))
+
+function dissipation_transpose_lower_closure_stencils(interior_weights)
+    closure = ntuple(i->dissipation_transpose_lower_closure_stencil(interior_weights, i), length(interior_weights))
+
+    N = maximum(s->length(s.weights), closure)
+    return right_pad.(closure, N)
+end
+
+function dissipation_transpose_upper_closure_stencils(interior_weights)
+    closure = reverse(ntuple(i->dissipation_transpose_upper_closure_stencil(interior_weights, i), length(interior_weights)))
+
+    N = maximum(s->length(s.weights), closure)
+    return left_pad.(closure, N)
+end
+
+
+function dissipation_transpose_lower_closure_stencil(interior_weights, i)
+    w = ntuple(k->interior_weights[i], dissipation_lower_closure_size(interior_weights))
+
+    for k ∈ i:-1:1
+        w = (w..., interior_weights[k])
+    end
+
+    return Stencil(w..., center = i)
+end
+
+function dissipation_transpose_upper_closure_stencil(interior_weights, i)
+    j = length(interior_weights)+1-i
+    w = ntuple(k->interior_weights[j], dissipation_upper_closure_size(interior_weights))
+
+    for k ∈ j:1:length(interior_weights)
+        w = (interior_weights[k], w...)
+    end
+
+    return Stencil(w..., center = length(interior_weights)-midpoint(interior_weights)+1)
+end
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/volumeops/derivatives/second_derivative_variable.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,195 @@
+export SecondDerivativeVariable
+
+# REVIEW: Fixa docs
+"""
+    SecondDerivativeVariable{Dir,T,D,...} <: LazyTensor{T,D,D}
+
+A second derivative operator in direction `Dir` with a variable coefficient.
+"""
+struct SecondDerivativeVariable{Dir,T,D,M,IStencil<:NestedStencil{T},CStencil<:NestedStencil{T},TArray<:AbstractArray} <: LazyTensor{T,D,D}
+    inner_stencil::IStencil
+    closure_stencils::NTuple{M,CStencil}
+    size::NTuple{D,Int}
+    coefficient::TArray
+
+    function SecondDerivativeVariable{Dir, D}(inner_stencil::NestedStencil{T}, closure_stencils::NTuple{M,NestedStencil{T}}, size::NTuple{D,Int}, coefficient::AbstractArray) where {Dir,T,D,M}
+        IStencil = typeof(inner_stencil)
+        CStencil = eltype(closure_stencils)
+        TArray = typeof(coefficient)
+        return new{Dir,T,D,M,IStencil,CStencil,TArray}(inner_stencil,closure_stencils,size, coefficient)
+    end
+end
+
+function SecondDerivativeVariable(grid::EquidistantGrid, coeff::AbstractArray, inner_stencil, closure_stencils, dir)
+    check_coefficient(grid, coeff)
+
+    Δxᵢ = spacing(grid)[dir]
+    scaled_inner_stencil = scale(inner_stencil, 1/Δxᵢ^2)
+    scaled_closure_stencils = scale.(Tuple(closure_stencils), 1/Δxᵢ^2)
+    return SecondDerivativeVariable{dir, dimension(grid)}(scaled_inner_stencil, scaled_closure_stencils, size(grid), coeff)
+end
+
+function SecondDerivativeVariable(grid::EquidistantGrid{1}, coeff::AbstractVector, inner_stencil::NestedStencil, closure_stencils)
+    return SecondDerivativeVariable(grid, coeff, inner_stencil, closure_stencils, 1)
+end
+
+@doc raw"""
+    SecondDerivativeVariable(grid::EquidistantGrid, coeff::AbstractArray, stencil_set, dir)
+
+Create a `LazyTensor` for the second derivative with a variable coefficient
+`coeff` on `grid` from the stencils in `stencil_set`. The direction is
+determined by `dir`.
+
+`coeff` is a grid function on `grid`.
+
+# Example
+With
+```
+D = SecondDerivativeVariable(g, c, stencil_set, 2)
+```
+then `D*u` approximates
+```math
+\frac{\partial}{\partial y} c(x,y) \frac{\partial u}{\partial y},
+```
+on ``(0,1)⨯(0,1)`` represented by `g`.
+"""
+function SecondDerivativeVariable(grid::EquidistantGrid, coeff::AbstractArray, stencil_set, dir::Int)
+    inner_stencil    = parse_nested_stencil(eltype(coeff), stencil_set["D2variable"]["inner_stencil"])
+    closure_stencils = parse_nested_stencil.(eltype(coeff), stencil_set["D2variable"]["closure_stencils"])
+
+    return SecondDerivativeVariable(grid, coeff, inner_stencil, closure_stencils, dir)
+end
+
+function check_coefficient(grid, coeff)
+    if dimension(grid) != ndims(coeff)
+        throw(ArgumentError("The coefficient has dimension $(ndims(coeff)) while the grid is dimension $(dimension(grid))"))
+    end
+
+    if size(grid) != size(coeff)
+        throw(DimensionMismatch("the size $(size(coeff)) of the coefficient does not match the size $(size(grid)) of the grid"))
+    end
+end
+
+derivative_direction(::SecondDerivativeVariable{Dir}) where {Dir} = Dir
+
+closure_size(op::SecondDerivativeVariable) = length(op.closure_stencils)
+
+LazyTensors.range_size(op::SecondDerivativeVariable) = op.size
+LazyTensors.domain_size(op::SecondDerivativeVariable) = op.size
+
+
+function derivative_view(op, a, I)
+    d = derivative_direction(op)
+
+    Iview = Base.setindex(I,:,d)
+    return @view a[Iview...]
+end
+
+function apply_lower(op::SecondDerivativeVariable, v, I...)
+    ṽ = derivative_view(op, v, I)
+    c̃ = derivative_view(op, op.coefficient, I)
+
+    i = I[derivative_direction(op)]
+    return @inbounds apply_stencil(op.closure_stencils[i], c̃, ṽ, i)
+end
+
+function apply_interior(op::SecondDerivativeVariable, v, I...)
+    ṽ = derivative_view(op, v, I)
+    c̃ = derivative_view(op, op.coefficient, I)
+
+    i = I[derivative_direction(op)]
+    return apply_stencil(op.inner_stencil, c̃, ṽ, i)
+end
+
+function apply_upper(op::SecondDerivativeVariable, v, I...)
+    ṽ = derivative_view(op, v, I)
+    c̃ = derivative_view(op, op.coefficient, I)
+
+    i = I[derivative_direction(op)]
+    stencil = op.closure_stencils[op.size[derivative_direction(op)]-i+1]
+    return @inbounds apply_stencil_backwards(stencil, c̃, ṽ, i)
+end
+
+function LazyTensors.apply(op::SecondDerivativeVariable, v::AbstractArray, I::Vararg{Index})
+    if I[derivative_direction(op)] isa Index{Lower}
+        return apply_lower(op, v, Int.(I)...)
+    elseif I[derivative_direction(op)] isa Index{Upper}
+        return apply_upper(op, v, Int.(I)...)
+    elseif I[derivative_direction(op)] isa Index{Interior}
+        return apply_interior(op, v, Int.(I)...)
+    else
+        error("Invalid region")
+    end
+end
+
+function LazyTensors.apply(op::SecondDerivativeVariable, v::AbstractArray, I...)
+    dir = derivative_direction(op)
+
+    i = I[dir]
+
+    I = map(i->Index(i, Interior), I)
+    if 0 < i <= closure_size(op)
+        I = Base.setindex(I, Index(i, Lower), dir)
+        return LazyTensors.apply(op, v, I...)
+    elseif closure_size(op) < i <= op.size[dir]-closure_size(op)
+        I = Base.setindex(I, Index(i, Interior), dir)
+        return LazyTensors.apply(op, v, I...)
+    elseif op.size[dir]-closure_size(op) < i <= op.size[dir]
+        I = Base.setindex(I, Index(i, Upper), dir)
+        return LazyTensors.apply(op, v, I...)
+    else
+        error("Bounds error") # TODO: Make this more standard
+    end
+end
+
+
+## 2D Specific implementations to avoid instability
+## TODO: Should really be solved by fixing the general methods instead
+
+
+## x-direction
+function apply_lower(op::SecondDerivativeVariable{1}, v, i, j)
+    ṽ = @view v[:,j]
+    c̃ = @view op.coefficient[:,j]
+
+    return @inbounds apply_stencil(op.closure_stencils[i], c̃, ṽ, i)
+end
+
+function apply_interior(op::SecondDerivativeVariable{1}, v, i, j)
+    ṽ = @view v[:,j]
+    c̃ = @view op.coefficient[:,j]
+
+    return @inbounds apply_stencil(op.inner_stencil, c̃, ṽ, i)
+end
+
+function apply_upper(op::SecondDerivativeVariable{1}, v, i, j)
+    ṽ = @view v[:,j]
+    c̃ = @view op.coefficient[:,j]
+
+    stencil = op.closure_stencils[op.size[derivative_direction(op)]-i+1]
+    return @inbounds apply_stencil_backwards(stencil, c̃, ṽ, i)
+end
+
+
+## y-direction
+function apply_lower(op::SecondDerivativeVariable{2}, v, i, j)
+    ṽ = @view v[i,:]
+    c̃ = @view op.coefficient[i,:]
+
+    return @inbounds apply_stencil(op.closure_stencils[j], c̃, ṽ, j)
+end
+
+function apply_interior(op::SecondDerivativeVariable{2}, v, i, j)
+    ṽ = @view v[i,:]
+    c̃ = @view op.coefficient[i,:]
+
+    return @inbounds apply_stencil(op.inner_stencil, c̃, ṽ, j)
+end
+
+function apply_upper(op::SecondDerivativeVariable{2}, v, i, j)
+    ṽ = @view v[i,:]
+    c̃ = @view op.coefficient[i,:]
+
+    stencil = op.closure_stencils[op.size[derivative_direction(op)]-j+1]
+    return @inbounds apply_stencil_backwards(stencil, c̃, ṽ, j)
+end
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/volumeops/inference_trouble.txt	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,53 @@
+Innan ändringarna på den här branchen:
+
+begin
+    using Sbplib
+    using Sbplib.Grids
+    using Sbplib.SbpOperators
+
+    g = EquidistantGrid((10,10),(0.,0.), (1.,1.))
+    v = evalOn(g, (x,y)->x^2+y^2+1)
+    H = inner_product(g, 1., [1/2])
+end
+
+# Not type stable
+LazyTensors.apply(H.t1, H.t2*v, 1,2) 
+@code_warntype LazyTensors.apply(H.t1, H.t2*v, 1,2)
+@code_warntype LazyTensors.apply(H.t1.tm, view(H.t2*v,:,1), 2)
+
+# Nedan är halvdåliga
+@code_warntype LazyTensors.apply(H.t1.tm, view(H.t2*v,1,:), 2)
+@code_warntype LazyTensors.apply(H.t1.tm, view(v,1,:), 2)
+@code_warntype LazyTensors.apply(H.t1.tm, view(v,:,1), 2)
+@code_warntype LazyTensors.apply(H.t1.tm, v[:,1], 2)
+
+
+
+
+
+
+
+
+
+begin
+    using Sbplib
+    using Sbplib.Grids
+    using Sbplib.SbpOperators
+    import Sbplib.SbpOperators: Stencil
+    using Sbplib.RegionIndices
+
+    g = EquidistantGrid(10,0., 1.)
+    v = evalOn(g, (x)->x^2+1)
+    H = inner_product(g, 1., [1/2])
+    V = SbpOperators.volume_operator(g, Stencil(1.,center=1), (Stencil(1/2,center=1),), SbpOperators.even,1)
+    b = SbpOperators.boundary_operator(g, Stencil(1/2,center=1), CartesianBoundary{1,Lower}())
+end
+
+@code_warntype LazyTensors.apply(H, H*v, 2)
+@code_warntype LazyTensors.apply(V, V*v, 2)
+@code_warntype LazyTensors.apply(b, b*v, 2)
+
+
+
+begin
+end
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/volumeops/stencil_operator_distinct_closures.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,58 @@
+function stencil_operator_distinct_closures(grid::EquidistantGrid, inner_stencil, lower_closure, upper_closure, direction)
+    op = StencilOperatorDistinctClosures(restrict(grid, direction), inner_stencil, lower_closure, upper_closure)
+    return LazyTensors.inflate(op, size(grid), direction)
+end
+
+"""
+    StencilOperatorDistinctClosures{T,K,N,M,L} <: LazyTensor{T,1}
+
+A one dimensional stencil operator with separate closures for the two boundaries.
+
+`StencilOperatorDistinctClosures` can be contrasted to `VolumeOperator` in
+that it has different closure stencils for the upper and lower boundary.
+`VolumeOperator` uses the same closure for both boundaries. Having distinct
+closures is useful for representing operators with skewed stencils like upwind
+operators.
+
+See also: [`VolumeOperator`](@ref)
+"""
+struct StencilOperatorDistinctClosures{T,K,N,M,LC<:NTuple{N,Stencil{T,L}} where L, UC<:NTuple{M,Stencil{T,L}} where L} <: LazyTensor{T,1,1}
+    inner_stencil::Stencil{T,K}
+    lower_closure::LC
+    upper_closure::UC
+    size::Tuple{Int}
+end
+
+function StencilOperatorDistinctClosures(grid::EquidistantGrid{1}, inner_stencil, lower_closure, upper_closure)
+    return StencilOperatorDistinctClosures(inner_stencil, Tuple(lower_closure), Tuple(upper_closure), size(grid))
+end
+
+lower_closure_size(::StencilOperatorDistinctClosures{T,K,N,M}) where {T,K,N,M} = N
+upper_closure_size(::StencilOperatorDistinctClosures{T,K,N,M}) where {T,K,N,M} = M
+
+LazyTensors.range_size(op::StencilOperatorDistinctClosures) = op.size
+LazyTensors.domain_size(op::StencilOperatorDistinctClosures) = op.size
+
+function LazyTensors.apply(op::StencilOperatorDistinctClosures, v::AbstractVector, i::Index{Lower})
+    return @inbounds apply_stencil(op.lower_closure[Int(i)], v, Int(i))
+end
+
+function LazyTensors.apply(op::StencilOperatorDistinctClosures, v::AbstractVector, i::Index{Interior})
+    return apply_stencil(op.inner_stencil, v, Int(i))
+end
+
+function LazyTensors.apply(op::StencilOperatorDistinctClosures, v::AbstractVector, i::Index{Upper})
+    stencil_index = Int(i) - (op.size[1]-upper_closure_size(op))
+    return @inbounds apply_stencil(op.upper_closure[stencil_index], v, Int(i))
+end
+
+function LazyTensors.apply(op::StencilOperatorDistinctClosures, v::AbstractVector, i)
+    if i <= lower_closure_size(op)
+        LazyTensors.apply(op, v, Index(i, Lower))
+    elseif i > op.size[1]-upper_closure_size(op)
+        LazyTensors.apply(op, v, Index(i, Upper))
+    else
+        LazyTensors.apply(op, v, Index(i, Interior))
+    end
+end
+# TODO: Move this to LazyTensors when we have the region communication down.
--- a/src/SbpOperators/volumeops/volume_operator.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/src/SbpOperators/volumeops/volume_operator.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -12,16 +12,10 @@
 function volume_operator(grid::EquidistantGrid, inner_stencil, closure_stencils, parity, direction)
     #TODO: Check that direction <= Dim?
 
-    # Create 1D volume operator in along coordinate direction
     op = VolumeOperator(restrict(grid, direction), inner_stencil, closure_stencils, parity)
-    # 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 volume operator
-    parts = Base.setindex(Is, op, direction)
-    return foldl(⊗, parts)
+    return LazyTensors.inflate(op, size(grid), direction)
 end
+# TBD: Should the inflation happen here or should we remove this method and do it at the caller instead?
 
 """
     VolumeOperator{T,N,M,K} <: LazyTensor{T,1,1}
@@ -56,6 +50,6 @@
 end
 
 function LazyTensors.apply(op::VolumeOperator, v::AbstractVector, i)
-    r = getregion(i, closure_size(op), op.size[1])
-    return LazyTensors.apply(op, v, Index(i, r))
+    return LazyTensors.apply_with_region(op, v, closure_size(op), op.size[1], i)
 end
+# TODO: Move this to LazyTensors when we have the region communication down.
--- a/test/LazyTensors/lazy_tensor_operations_test.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/test/LazyTensors/lazy_tensor_operations_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -358,3 +358,17 @@
         @test I1⊗Ã⊗I2 == InflatedTensor(I1, Ã, I2)
     end
 end
+
+@testset "inflate" begin
+    I = LazyTensors.inflate(IdentityTensor(),(3,4,5,6), 2)
+    @test I isa LazyTensor{Float64, 3,3}
+    @test range_size(I) == (3,5,6)
+    @test domain_size(I) == (3,5,6)
+
+    @test LazyTensors.inflate(ScalingTensor(1., (4,)),(3,4,5,6), 1) == InflatedTensor(IdentityTensor{Float64}(),ScalingTensor(1., (4,)),IdentityTensor(4,5,6))
+    @test LazyTensors.inflate(ScalingTensor(2., (1,)),(3,4,5,6), 2) == InflatedTensor(IdentityTensor(3),ScalingTensor(2., (1,)),IdentityTensor(5,6))
+    @test LazyTensors.inflate(ScalingTensor(3., (6,)),(3,4,5,6), 4) == InflatedTensor(IdentityTensor(3,4,5),ScalingTensor(3., (6,)),IdentityTensor{Float64}())
+
+    @test_throws BoundsError LazyTensors.inflate(ScalingTensor(1., (4,)),(3,4,5,6), 0)
+    @test_throws BoundsError LazyTensors.inflate(ScalingTensor(1., (4,)),(3,4,5,6), 5)
+end
--- a/test/LazyTensors/tuple_manipulation_test.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/test/LazyTensors/tuple_manipulation_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -60,3 +60,19 @@
     @test LazyTensors.flatten_tuple((1,2,(3,(4,5)),6)) == (1,2,3,4,5,6)
     @test LazyTensors.flatten_tuple(((1,2),(3,4),(5,),6)) == (1,2,3,4,5,6)
 end
+
+@testset "left_pad_tuple" begin
+    @test LazyTensors.left_pad_tuple((1,2), 0, 2) == (1,2)
+    @test LazyTensors.left_pad_tuple((1,2), 0, 3) == (0,1,2)
+    @test LazyTensors.left_pad_tuple((3,2), 1, 6) == (1,1,1,1,3,2)
+
+    @test_throws DomainError(0, "Can't pad tuple of length 2 to 0 elements") LazyTensors.left_pad_tuple((1,2), 0, 0) == (1,2)
+end
+
+@testset "right_pad_tuple" begin
+    @test LazyTensors.right_pad_tuple((1,2), 0, 2) == (1,2)
+    @test LazyTensors.right_pad_tuple((1,2), 0, 3) == (1,2,0)
+    @test LazyTensors.right_pad_tuple((3,2), 1, 6) == (3,2,1,1,1,1)
+
+    @test_throws DomainError(0, "Can't pad tuple of length 2 to 0 elements") LazyTensors.right_pad_tuple((1,2), 0, 0) == (1,2)
+end
--- a/test/SbpOperators/stencil_set_test.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/test/SbpOperators/stencil_set_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -4,6 +4,7 @@
 using Sbplib.SbpOperators
 
 import Sbplib.SbpOperators.Stencil
+import Sbplib.SbpOperators.NestedStencil
 
 @testset "readoperator" begin
     toml_str = """
@@ -170,3 +171,18 @@
     @test SbpOperators.parse_rational(2) isa Rational
     @test SbpOperators.parse_rational(2) == 2//1
 end
+
+@testset "parse_nested_stencil" begin
+    toml = TOML.parse("""
+        s1 = [["1/2", "1/2", "0"],[ "-1/2", "-1", "-1/2"],["0", "1/2", "1/2"]]
+        s2 = {s = [[  "2",  "-1", "0"],[   "-3",  "1",    "0"],["1",   "0",   "0"]], c = 1}
+        s3 = {s = [[  "2",  "-1", "0"],[   "-3",  "1",    "0"],["1",   "0",   "0"]], c = 2}
+    """)
+
+    @test parse_nested_stencil(toml["s1"]) == CenteredNestedStencil((1//2, 1//2, 0//1),( -1//2, -1//1, -1//2),(0//1, 1//2, 1//2))
+    @test parse_nested_stencil(toml["s2"]) == NestedStencil((2//1, -1//1, 0//1),( -3//1, 1//1, 0//1),(1//1, 0//1, 0//1), center = 1)
+    @test parse_nested_stencil(toml["s3"]) == NestedStencil((2//1, -1//1, 0//1),( -3//1, 1//1, 0//1),(1//1, 0//1, 0//1), center = 2)
+
+    @test parse_nested_stencil(Float64, toml["s1"]) == CenteredNestedStencil((1/2, 1/2, 0.),( -1/2, -1., -1/2),(0., 1/2, 1/2))
+    @test parse_nested_stencil(Int, toml["s2"]) == NestedStencil((2, -1, 0),( -3, 1, 0),(1, 0, 0), center = 1)
+end
--- a/test/SbpOperators/stencil_test.jl	Tue Apr 26 14:28:42 2022 +0200
+++ b/test/SbpOperators/stencil_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -62,6 +62,23 @@
     end
 end
 
+@testset "left_pad" begin
+    @test SbpOperators.left_pad(Stencil(1,1, center = 1), 2) == Stencil(1,1, center=1)
+    @test SbpOperators.left_pad(Stencil(1,1, center = 1), 3) == Stencil(0,1,1, center=2)
+    @test SbpOperators.left_pad(Stencil(2,3, center = 2), 4) == Stencil(0,0,2,3, center=4)
+
+    @test SbpOperators.left_pad(Stencil(2.,3., center = 2), 4) == Stencil(0.,0.,2.,3., center=4)
+end
+
+@testset "right_pad" begin
+    @test SbpOperators.right_pad(Stencil(1,1, center = 1), 2) == Stencil(1,1, center=1)
+    @test SbpOperators.right_pad(Stencil(1,1, center = 1), 3) == Stencil(1,1,0, center=1)
+    @test SbpOperators.right_pad(Stencil(2,3, center = 2), 4) == Stencil(2,3,0,0, center=2)
+
+    @test SbpOperators.right_pad(Stencil(2.,3., center = 2), 4) == Stencil(2.,3.,0.,0., center=2)
+end
+
+
 @testset "NestedStencil" begin
 
     @testset "Constructors" begin
@@ -170,5 +187,4 @@
         @inferred SbpOperators.apply_stencil_backwards(s_int,   c_float, v_float, 2)
         @inferred SbpOperators.apply_stencil_backwards(s_float, c_float, v_int,   2)
     end
-
 end
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/SbpOperators/volumeops/derivatives/dissipation_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,217 @@
+using Test
+
+using Sbplib.SbpOperators
+using Sbplib.Grids
+using Sbplib.LazyTensors
+
+using Sbplib.SbpOperators: Stencil
+
+using Sbplib.SbpOperators: dissipation_interior_weights
+using Sbplib.SbpOperators: dissipation_interior_stencil, dissipation_transpose_interior_stencil
+using Sbplib.SbpOperators: midpoint, midpoint_transpose
+using Sbplib.SbpOperators: dissipation_lower_closure_size, dissipation_upper_closure_size
+using Sbplib.SbpOperators: dissipation_lower_closure_stencils,dissipation_upper_closure_stencils
+using Sbplib.SbpOperators: dissipation_transpose_lower_closure_stencils, dissipation_transpose_upper_closure_stencils
+
+"""
+    monomial(x,k)
+
+Evaluates ``x^k/k!` with the convetion that it is ``0`` for all ``k<0``.
+Has the property that ``d/dx monomial(x,k) = monomial(x,k-1)``
+"""
+function monomial(x,k)
+    if k < 0
+        return zero(x)
+    end
+    x^k/factorial(k)
+end
+
+@testset "undivided_dissipation" begin
+    g = EquidistantGrid(20, 0., 11.)
+    D,Dᵀ = undivided_dissipation(g, 1)
+
+    @test D isa LazyTensor{Float64,1,1} where T
+    @test Dᵀ isa LazyTensor{Float64,1,1} where T
+
+     @testset "Accuracy conditions" begin
+        N = 20
+        g = EquidistantGrid(N, 0//1,2//1)
+        h = only(spacing(g))
+        @testset "D_$p" for p ∈ [1,2,3,4]
+            D,Dᵀ = undivided_dissipation(g, p)
+
+            @testset "x^$k" for k ∈ 0:p
+                v  = evalOn(g, x->monomial(x,k))
+                vₚₓ = evalOn(g, x->monomial(x,k-p))
+
+                @test D*v == h^p * vₚₓ
+            end
+        end
+    end
+
+    @testset "tanspose equality" begin
+        function get_matrix(D)
+            N = only(range_size(D))
+            M = only(domain_size(D))
+
+            Dmat = zeros(N,M)
+            e = zeros(M)
+            for i ∈ 1:M
+                if i > 1
+                    e[i-1] = 0.
+                end
+                e[i] = 1.
+                Dmat[:,i] = D*e
+            end
+
+            return Dmat
+        end
+
+        g = EquidistantGrid(11, 0., 1.)
+        @testset "D_$p" for p ∈ [1,2,3,4]
+            D,Dᵀ = undivided_dissipation(g, p)
+
+            D̄  = get_matrix(D)
+            D̄ᵀ = get_matrix(Dᵀ)
+
+            @test D̄ == D̄ᵀ'
+        end
+    end
+end
+
+@testset "dissipation_interior_weights" begin
+    @test dissipation_interior_weights(1) == (-1, 1)
+    @test dissipation_interior_weights(2) == (1,-2, 1)
+    @test dissipation_interior_weights(3) == (-1, 3,-3, 1)
+    @test dissipation_interior_weights(4) == (1, -4, 6, -4, 1)
+end
+
+@testset "dissipation_interior_stencil" begin
+    @test dissipation_interior_stencil(dissipation_interior_weights(1)) == Stencil(-1, 1, center=2)
+    @test dissipation_interior_stencil(dissipation_interior_weights(2)) == Stencil( 1,-2, 1, center=2)
+    @test dissipation_interior_stencil(dissipation_interior_weights(3)) == Stencil(-1, 3,-3, 1, center=3)
+    @test dissipation_interior_stencil(dissipation_interior_weights(4)) == Stencil( 1,-4, 6,-4, 1, center=3)
+end
+
+@testset "dissipation_transpose_interior_stencil" begin
+    @test dissipation_transpose_interior_stencil(dissipation_interior_weights(1)) == Stencil(1,-1, center=1)
+    @test dissipation_transpose_interior_stencil(dissipation_interior_weights(2)) == Stencil(1,-2, 1, center=2)
+    @test dissipation_transpose_interior_stencil(dissipation_interior_weights(3)) == Stencil(1,-3, 3,-1, center=2)
+    @test dissipation_transpose_interior_stencil(dissipation_interior_weights(4)) == Stencil(1,-4, 6,-4, 1, center=3)
+end
+
+@testset "midpoint" begin
+    @test midpoint((1,1)) == 2
+    @test midpoint((1,1,1)) == 2
+    @test midpoint((1,1,1,1)) == 3
+    @test midpoint((1,1,1,1,1)) == 3
+end
+
+@testset "midpoint_transpose" begin
+    @test midpoint_transpose((1,1)) == 1
+    @test midpoint_transpose((1,1,1)) == 2
+    @test midpoint_transpose((1,1,1,1)) == 2
+    @test midpoint_transpose((1,1,1,1,1)) == 3
+end
+
+@testset "dissipation_lower_closure_size" begin
+    @test dissipation_lower_closure_size((1,1)) == 1
+    @test dissipation_lower_closure_size((1,1,1)) == 1
+    @test dissipation_lower_closure_size((1,1,1,1)) == 2
+    @test dissipation_lower_closure_size((1,1,1,1,1)) == 2
+end
+
+@testset "dissipation_upper_closure_size" begin
+    @test dissipation_upper_closure_size((1,1)) == 0
+    @test dissipation_upper_closure_size((1,1,1)) == 1
+    @test dissipation_upper_closure_size((1,1,1,1)) == 1
+    @test dissipation_upper_closure_size((1,1,1,1,1)) == 2
+end
+
+@testset "dissipation_lower_closure_stencils" begin
+    cases = (
+        (-1,1) => (
+            Stencil(-1, 1, center=1),
+        ),
+        (1,-2,1) => (
+            Stencil( 1,-2, 1, center=1),
+        ),
+        (-1,3,-3,1) => (
+            Stencil(-1,3,-3,1, center=1),
+            Stencil(-1,3,-3,1, center=2),
+        ),
+        (1, -4, 6, -4, 1) => (
+            Stencil(1, -4, 6, -4, 1, center=1),
+            Stencil(1, -4, 6, -4, 1, center=2),
+        )
+    )
+    @testset "interior_weights = $w" for (w, closure_stencils) ∈ cases
+        @test dissipation_lower_closure_stencils(w) == closure_stencils
+    end
+end
+
+@testset "dissipation_upper_closure_stencils" begin
+    cases = (
+        (-1,1) => (),
+        (1,-2,1) => (
+            Stencil( 1,-2, 1, center=3),
+        ),
+        (-1,3,-3,1) => (
+            Stencil(-1,3,-3,1, center=4),
+        ),
+        (1, -4, 6, -4, 1) => (
+            Stencil(1, -4, 6, -4, 1, center=4),
+            Stencil(1, -4, 6, -4, 1, center=5),
+        )
+    )
+    @testset "interior_weights = $w" for (w, closure_stencils) ∈ cases
+        @test dissipation_upper_closure_stencils(w) == closure_stencils
+    end
+end
+
+
+@testset "dissipation_transpose_lower_closure_stencils" begin
+    cases = (
+        (-1,1) => (
+            Stencil(-1,-1, 0, center=1),
+            Stencil( 1, 1,-1, center=2),
+        ),
+        (1,-2,1) => (
+            Stencil( 1, 1, 0, 0, center=1),
+            Stencil(-2,-2, 1, 0, center=2),
+            Stencil( 1, 1,-2, 1, center=3),
+        ),
+        (-1,3,-3,1) => (
+            Stencil(-1,-1,-1, 0, 0, 0, center=1),
+            Stencil( 3, 3, 3,-1, 0, 0, center=2),
+            Stencil(-3,-3,-3, 3,-1, 0, center=3),
+            Stencil( 1, 1, 1,-3, 3,-1, center=4),
+        ),
+    )
+    @testset "interior_weights = $w" for (w, closure_stencils) ∈ cases
+        @test dissipation_transpose_lower_closure_stencils(w) == closure_stencils
+    end
+end
+
+@testset "dissipation_transpose_upper_closure_stencils" begin
+    cases = (
+        (-1,1) => (
+            Stencil( 1,-1, center = 1),
+            Stencil( 0, 1, center = 2),
+        ),
+        (1,-2,1) => (
+            Stencil( 1,-2, 1, 1, center=2),
+            Stencil( 0, 1,-2,-2, center=3),
+            Stencil( 0, 0, 1, 1, center=4),
+        ),
+        (-1,3,-3,1) => (
+            Stencil( 1,-3, 3,-1,-1, center=2),
+            Stencil( 0, 1,-3, 3, 3, center=3),
+            Stencil( 0, 0, 1,-3,-3, center=4),
+            Stencil( 0, 0, 0, 1, 1, center=5),
+        ),
+    )
+    @testset "interior_weights = $w" for (w, closure_stencils) ∈ cases
+        @test dissipation_transpose_upper_closure_stencils(w) == closure_stencils
+    end
+end
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/SbpOperators/volumeops/derivatives/second_derivative_variable_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,187 @@
+using Test
+
+using Sbplib.Grids
+using Sbplib.LazyTensors
+using Sbplib.SbpOperators
+using Sbplib.RegionIndices
+using Sbplib.SbpOperators: NestedStencil, CenteredNestedStencil
+
+using LinearAlgebra
+
+@testset "SecondDerivativeVariable" begin
+    interior_stencil = CenteredNestedStencil((1/2, 1/2, 0.),(-1/2, -1., -1/2),( 0., 1/2, 1/2))
+    closure_stencils = [
+        NestedStencil(( 2.,  -1., 0.),(-3., 1.,  0.), (1., 0., 0.), center = 1),
+    ]
+
+    @testset "1D" begin
+        g = EquidistantGrid(11, 0., 1.)
+        c = [  1.,  3.,  6., 10., 15., 21., 28., 36., 45., 55., 66.]
+        @testset "Constructors" begin
+            @test SecondDerivativeVariable(g, c, interior_stencil, closure_stencils) isa LazyTensor
+
+            D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils)
+            @test range_dim(D₂ᶜ) == 1
+            @test domain_dim(D₂ᶜ) == 1
+
+
+            stencil_set = read_stencil_set(sbp_operators_path()*"standard_diagonal.toml"; order = 2)
+            @test SecondDerivativeVariable(g, c, stencil_set, 1) isa SecondDerivativeVariable
+
+            @testset "checking c" begin
+                c_short = rand(5)
+                c_long = rand(16)
+                c_higher_dimension = rand(11,11)
+
+                @test_throws DimensionMismatch("the size (5,) of the coefficient does not match the size (11,) of the grid") SecondDerivativeVariable(g, c_short, interior_stencil, closure_stencils)
+                @test_throws DimensionMismatch("the size (16,) of the coefficient does not match the size (11,) of the grid") SecondDerivativeVariable(g, c_long, interior_stencil, closure_stencils)
+                @test_throws ArgumentError("The coefficient has dimension 2 while the grid is dimension 1") SecondDerivativeVariable(g, c_higher_dimension, interior_stencil, closure_stencils,1)
+            end
+        end
+
+        @testset "sizes" begin
+            D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils)
+            @test closure_size(D₂ᶜ) == 1
+            @test range_size(D₂ᶜ) == (11,)
+            @test domain_size(D₂ᶜ) == (11,)
+        end
+
+        @testset "application" begin
+
+            function apply_to_functions(; v, c)
+                g = EquidistantGrid(11, 0., 10.) # h = 1
+                c̄ = evalOn(g,c)
+                v̄ = evalOn(g,v)
+
+                D₂ᶜ = SecondDerivativeVariable(g, c̄, interior_stencil, closure_stencils)
+                return D₂ᶜ*v̄
+            end
+
+            @test apply_to_functions(v=x->1.,  c=x-> -1.) == zeros(11)
+            @test apply_to_functions(v=x->1.,  c=x-> -x ) == zeros(11)
+            @test apply_to_functions(v=x->x,   c=x->  1.) == zeros(11)
+            @test apply_to_functions(v=x->x,   c=x-> -x ) == -ones(11)
+            @test apply_to_functions(v=x->x^2, c=x->  1.) == 2ones(11)
+        end
+
+        @testset "type stability" begin
+            g = EquidistantGrid(11, 0., 10.) # h = 1
+            c̄ = evalOn(g,x-> -1)
+            v̄ = evalOn(g,x->1.)
+
+            D₂ᶜ = SecondDerivativeVariable(g, c̄, interior_stencil, closure_stencils)
+
+            @inferred SbpOperators.apply_lower(D₂ᶜ, v̄, 1)
+            @inferred SbpOperators.apply_interior(D₂ᶜ, v̄, 5)
+            @inferred SbpOperators.apply_upper(D₂ᶜ, v̄, 11)
+            @inferred (D₂ᶜ*v̄)[Index(1,Lower)]
+        end
+    end
+
+    @testset "2D" begin
+        g = EquidistantGrid((11,9), (0.,0.), (10.,8.)) # h = 1
+        c = evalOn(g, (x,y)->x+y)
+        @testset "Constructors" begin
+            @test SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,1) isa LazyTensor
+            @test SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,2) isa LazyTensor
+
+            D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,1)
+            @test range_dim(D₂ᶜ) == 2
+            @test domain_dim(D₂ᶜ) == 2
+
+            stencil_set = read_stencil_set(sbp_operators_path()*"standard_diagonal.toml"; order = 2)
+            @test SecondDerivativeVariable(g, c, stencil_set, 1) isa SecondDerivativeVariable
+        end
+
+        @testset "sizes" begin
+            D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,1)
+            @test range_size(D₂ᶜ) == (11,9)
+            @test domain_size(D₂ᶜ) == (11,9)
+            @test closure_size(D₂ᶜ) == 1
+
+            D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,2)
+            @test range_size(D₂ᶜ) == (11,9)
+            @test domain_size(D₂ᶜ) == (11,9)
+            @test closure_size(D₂ᶜ) == 1
+        end
+
+        @testset "application" begin
+            function apply_to_functions(dir; v, c)
+                g = EquidistantGrid((11,9), (0.,0.), (10.,8.)) # h = 1
+                c̄ = evalOn(g,c)
+                v̄ = evalOn(g,v)
+
+                D₂ᶜ = SecondDerivativeVariable(g, c̄, interior_stencil, closure_stencils,dir)
+                return D₂ᶜ*v̄
+            end
+
+            # x-direction
+            @test apply_to_functions(1,v=(x,y)->1.,  c=(x,y)-> -1.) == zeros(11,9)
+            @test apply_to_functions(1,v=(x,y)->1.,  c=(x,y)->- x ) == zeros(11,9)
+            @test apply_to_functions(1,v=(x,y)->x,   c=(x,y)->  1.) == zeros(11,9)
+            @test apply_to_functions(1,v=(x,y)->x,   c=(x,y)-> -x ) == -ones(11,9)
+            @test apply_to_functions(1,v=(x,y)->x^2, c=(x,y)->  1.) == 2ones(11,9)
+
+            @test apply_to_functions(1,v=(x,y)->1.,  c=(x,y)->- y ) == zeros(11,9)
+            @test apply_to_functions(1,v=(x,y)->y,   c=(x,y)->  1.) == zeros(11,9)
+            @test apply_to_functions(1,v=(x,y)->y,   c=(x,y)-> -y ) == zeros(11,9)
+            @test apply_to_functions(1,v=(x,y)->y^2, c=(x,y)->  1.) == zeros(11,9)
+
+            # y-direction
+            @test apply_to_functions(2,v=(x,y)->1.,  c=(x,y)-> -1.) == zeros(11,9)
+            @test apply_to_functions(2,v=(x,y)->1.,  c=(x,y)->- y ) == zeros(11,9)
+            @test apply_to_functions(2,v=(x,y)->y,   c=(x,y)->  1.) == zeros(11,9)
+            @test apply_to_functions(2,v=(x,y)->y,   c=(x,y)-> -y ) == -ones(11,9)
+            @test apply_to_functions(2,v=(x,y)->y^2, c=(x,y)->  1.) == 2ones(11,9)
+
+            @test apply_to_functions(2,v=(x,y)->1.,  c=(x,y)->- x ) == zeros(11,9)
+            @test apply_to_functions(2,v=(x,y)->x,   c=(x,y)->  1.) == zeros(11,9)
+            @test apply_to_functions(2,v=(x,y)->x,   c=(x,y)-> -x ) == zeros(11,9)
+            @test apply_to_functions(2,v=(x,y)->x^2, c=(x,y)->  1.) == zeros(11,9)
+
+
+            @testset "standard diagonal operators" begin
+                c(x,y) = exp(x) + exp(1.5(1-y))
+                v(x,y) = sin(x) + cos(1.5(1-y))
+
+                Dxv(x,y) = cos(x)*exp(x) - (exp(x) + exp(1.5 - 1.5y))*sin(x)
+                Dyv(x,y) = -1.5(1.5exp(x) + 1.5exp(1.5 - 1.5y))*cos(1.5 - 1.5y) - 2.25exp(1.5 - 1.5y)*sin(1.5 - 1.5y)
+
+                g₁ = EquidistantGrid((60,67), (0.,0.), (1.,2.))
+                g₂ = refine(g₁,2)
+
+                c̄₁ = evalOn(g₁, c)
+                c̄₂ = evalOn(g₂, c)
+
+                v̄₁ = evalOn(g₁, v)
+                v̄₂ = evalOn(g₂, v)
+
+
+                function convergence_rate_estimate(stencil_set, dir, Dv_true)
+                    D₁ = SecondDerivativeVariable(g₁, c̄₁, stencil_set, dir)
+                    D₂ = SecondDerivativeVariable(g₂, c̄₂, stencil_set, dir)
+
+                    Dv̄₁ = D₁*v̄₁
+                    Dv̄₂ = D₂*v̄₂
+
+                    Dv₁ = evalOn(g₁,Dv_true)
+                    Dv₂ = evalOn(g₂,Dv_true)
+
+                    e₁ = norm(Dv̄₁ - Dv₁)/norm(Dv₁)
+                    e₂ = norm(Dv̄₂ - Dv₂)/norm(Dv₂)
+
+                    return log2(e₁/e₂)
+                end
+
+                stencil_set = read_stencil_set(sbp_operators_path()*"standard_diagonal.toml"; order = 2)
+                @test convergence_rate_estimate(stencil_set, 1, Dxv) ≈ 1.5 rtol = 1e-1
+                @test convergence_rate_estimate(stencil_set, 2, Dyv) ≈ 1.5 rtol = 1e-1
+
+                stencil_set = read_stencil_set(sbp_operators_path()*"standard_diagonal.toml"; order = 4)
+                @test convergence_rate_estimate(stencil_set, 1, Dxv) ≈ 2.5 rtol = 1e-1
+                @test convergence_rate_estimate(stencil_set, 2, Dyv) ≈ 2.5 rtol = 2e-1
+            end
+        end
+    end
+end
+
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/SbpOperators/volumeops/stencil_operator_distinct_closures_test.jl	Tue Apr 26 14:29:08 2022 +0200
@@ -0,0 +1,83 @@
+using Test
+
+using Sbplib.SbpOperators
+using Sbplib.Grids
+# using Sbplib.RegionIndices
+using Sbplib.LazyTensors
+
+import Sbplib.SbpOperators.Stencil
+import Sbplib.SbpOperators.StencilOperatorDistinctClosures
+import Sbplib.SbpOperators.stencil_operator_distinct_closures
+
+@testset "stencil_operator_distinct_closures" begin
+    lower_closure = (
+        Stencil(-1,1, center=1),
+    )
+
+    inner_stencil = Stencil(-2,2, center=1)
+
+    upper_closure = (
+        Stencil(-3,3, center=1),
+        Stencil(-4,4, center=2),
+    )
+
+    g₁ = EquidistantGrid(5, 0., 1.)
+    g₂ = EquidistantGrid((5,5), (0.,0.), (1.,1.))
+    h = 1/4
+
+    A₁  = stencil_operator_distinct_closures(g₁, inner_stencil, lower_closure, upper_closure, 1)
+    A₂¹ = stencil_operator_distinct_closures(g₂, inner_stencil, lower_closure, upper_closure, 1)
+    A₂² = stencil_operator_distinct_closures(g₂, inner_stencil, lower_closure, upper_closure, 2)
+
+    v₁ = evalOn(g₁, x->x)
+
+    u = [1., 2., 2., 3., 4.]*h
+    @test A₁*v₁ == u
+
+    v₂ = evalOn(g₂, (x,y)-> x + 3y)
+    @test A₂¹*v₂ == repeat(u, 1, 5)
+    @test A₂²*v₂ == repeat(3u', 5, 1)
+end
+
+@testset "StencilOperatorDistinctClosures" begin
+    g = EquidistantGrid(11, 0., 1.)
+
+    lower_closure = (
+        Stencil(-1,1, center=1),
+        Stencil(-2,2, center=2),
+    )
+
+    inner_stencil = Stencil(-3,3, center=1)
+
+    upper_closure = (
+        Stencil(4,-4,4, center=1),
+        Stencil(5,-5,5, center=2),
+        Stencil(6,-6,6, center=3),
+    )
+
+    A = StencilOperatorDistinctClosures(g, inner_stencil, lower_closure, upper_closure)
+    @test A isa LazyTensor{T,1,1} where T
+
+    @test SbpOperators.lower_closure_size(A) == 2
+    @test SbpOperators.upper_closure_size(A) == 3
+
+    @test domain_size(A) == (11,)
+    @test range_size(A) == (11,)
+
+    v = rand(11)
+    @testset "apply" begin
+        # Lower closure
+        @test LazyTensors.apply(A, v, 1) ≈ 1*(-v[1] + v[2])
+        @test LazyTensors.apply(A, v, 2) ≈ 2*(-v[1] + v[2])
+
+        # Interior
+        @test LazyTensors.apply(A, v, 3) ≈ 3*(-v[3] + v[4])
+        @test LazyTensors.apply(A, v, 4) ≈ 3*(-v[4] + v[5])
+        @test LazyTensors.apply(A, v, 8) ≈ 3*(-v[8] + v[9])
+
+        # Upper closure
+        @test LazyTensors.apply(A, v,  9) ≈ 4*(v[9] - v[10] + v[11])
+        @test LazyTensors.apply(A, v, 10) ≈ 5*(v[9] - v[10] + v[11])
+        @test LazyTensors.apply(A, v, 11) ≈ 6*(v[9] - v[10] + v[11])
+    end
+end