From 65c10e6c50e9fe1a2fc3ebd5f38eb36f5d3931a8 Mon Sep 17 00:00:00 2001
From: oscarddssmith <oscar.smith@juliacomputing.com>
Date: Thu, 1 Aug 2024 14:32:43 -0400
Subject: [PATCH 1/3] optimize StaticWOperator by using lu to allow saving the
 factorization

---
 .../src/derivative_utils.jl                            | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl b/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl
index ee2a9d4fd4..32b002c1f9 100644
--- a/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl
+++ b/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl
@@ -1,22 +1,24 @@
 const ROSENBROCK_INV_CUTOFF = 7 # https://github.com/SciML/OrdinaryDiffEq.jl/pull/1539
 
-struct StaticWOperator{isinv, T} <: AbstractSciMLOperator{T}
+struct StaticWOperator{isinv, T, F} <: AbstractSciMLOperator{T}
     W::T
+    F::F
     function StaticWOperator(W::T, callinv = true) where {T}
         isinv = size(W, 1) <= ROSENBROCK_INV_CUTOFF
 
+        F = lu(W, check=false)
         # when constructing W for the first time for the type
         # inv(W) can be singular
         _W = if isinv && callinv
-            inv(W)
+            F\typeof(W)(I)
         else
             W
         end
-        new{isinv, T}(_W)
+        new{isinv, T, typeof(F)}(_W, F)
     end
 end
 isinv(W::StaticWOperator{S}) where {S} = S
-Base.:\(W::StaticWOperator, v::AbstractArray) = isinv(W) ? W.W * v : W.W \ v
+Base.:\(W::StaticWOperator, v::AbstractArray) = isinv(W) ? W.W * v : W.F \ v
 
 function calc_tderivative!(integrator, cache, dtd1, repeat_step)
     @inbounds begin

From dc0161eecb3c8efd72644fd4ba569a86f0ed0b3e Mon Sep 17 00:00:00 2001
From: oscarddssmith <oscar.smith@juliacomputing.com>
Date: Wed, 14 Aug 2024 11:55:49 -0400
Subject: [PATCH 2/3] import lu

---
 .../src/OrdinaryDiffEqDifferentiation.jl                        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl b/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
index cffbf869cb..31bb6ea3e3 100644
--- a/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
+++ b/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
@@ -14,7 +14,7 @@ import FunctionWrappersWrappers
 using DiffEqBase
 
 import LinearAlgebra
-import LinearAlgebra: Diagonal, I, UniformScaling, diagind, mul!, lmul!, axpby!, opnorm
+import LinearAlgebra: Diagonal, I, UniformScaling, diagind, mul!, lmul!, axpby!, opnorm, lu
 import SparseArrays: SparseMatrixCSC, AbstractSparseMatrix, nonzeros
 
 import InteractiveUtils

From 9474b35e4a5e5bde37c4d50bfa2f4a47900ec942 Mon Sep 17 00:00:00 2001
From: oscarddssmith <oscar.smith@juliacomputing.com>
Date: Wed, 14 Aug 2024 12:48:22 -0400
Subject: [PATCH 3/3] improve performance

---
 .../src/OrdinaryDiffEqDifferentiation.jl            |  2 ++
 .../src/derivative_utils.jl                         | 13 ++++++++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl b/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
index 31bb6ea3e3..4fdbd9f54b 100644
--- a/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
+++ b/lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
@@ -15,12 +15,14 @@ using DiffEqBase
 
 import LinearAlgebra
 import LinearAlgebra: Diagonal, I, UniformScaling, diagind, mul!, lmul!, axpby!, opnorm, lu
+import LinearAlgebra: LowerTriangular, UpperTriangular
 import SparseArrays: SparseMatrixCSC, AbstractSparseMatrix, nonzeros
 
 import InteractiveUtils
 import ArrayInterface
 
 import StaticArrayInterface
+import StaticArrays
 import StaticArrays: SArray, MVector, SVector, @SVector, StaticArray, MMatrix, SA,
                      StaticMatrix
 
diff --git a/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl b/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl
index 32b002c1f9..a0f56c835b 100644
--- a/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl
+++ b/lib/OrdinaryDiffEqDifferentiation/src/derivative_utils.jl
@@ -4,13 +4,20 @@ struct StaticWOperator{isinv, T, F} <: AbstractSciMLOperator{T}
     W::T
     F::F
     function StaticWOperator(W::T, callinv = true) where {T}
-        isinv = size(W, 1) <= ROSENBROCK_INV_CUTOFF
+        n = size(W, 1)
+        isinv = n <= ROSENBROCK_INV_CUTOFF
 
-        F = lu(W, check=false)
+        F = if isinv && callinv
+            # this should be in ArrayInterface but can't be for silly reasons
+            # doing to how StaticArrays and StaticArraysCore are split up
+            StaticArrays.LU(LowerTriangular(W), UpperTriangular(W), SVector{n}(1:n))
+        else
+            lu(W, check=false)
+        end
         # when constructing W for the first time for the type
         # inv(W) can be singular
         _W = if isinv && callinv
-            F\typeof(W)(I)
+            inv(W)
         else
             W
         end