From 5211e189aa0c6b13c069da614a28cbc324e1423b Mon Sep 17 00:00:00 2001
From: Aayush Sabharwal <aayush.sabharwal@gmail.com>
Date: Thu, 28 Nov 2024 12:18:14 +0530
Subject: [PATCH 1/2] fix: handle `I` as mass matrix for `CheckInit`

---
 src/initialization.jl  |  1 +
 test/initialization.jl | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/initialization.jl b/src/initialization.jl
index 993d10686..4e976e168 100644
--- a/src/initialization.jl
+++ b/src/initialization.jl
@@ -123,6 +123,7 @@ function get_initial_values(
     t = current_time(integrator)
     M = f.mass_matrix
 
+    M == I && return u0, p, true
     algebraic_vars = [all(iszero, x) for x in eachcol(M)]
     algebraic_eqs = [all(iszero, x) for x in eachrow(M)]
     (iszero(algebraic_vars) || iszero(algebraic_eqs)) && return u0, p, true
diff --git a/test/initialization.jl b/test/initialization.jl
index e6211e59c..1ea1da694 100644
--- a/test/initialization.jl
+++ b/test/initialization.jl
@@ -1,4 +1,5 @@
-using StochasticDiffEq, OrdinaryDiffEq, NonlinearSolve, SymbolicIndexingInterface, Test
+using StochasticDiffEq, OrdinaryDiffEq, NonlinearSolve, SymbolicIndexingInterface,
+      LinearAlgebra, Test
 
 @testset "CheckInit" begin
     @testset "ODEProblem" begin
@@ -27,6 +28,20 @@ using StochasticDiffEq, OrdinaryDiffEq, NonlinearSolve, SymbolicIndexingInterfac
                 prob, integ, f, SciMLBase.CheckInit(),
                 Val(SciMLBase.isinplace(f)); abstol = 1e-10)
         end
+
+        @testset "With I mass matrix" begin
+            function rhs(u, p, t)
+                return u
+            end
+            prob = ODEProblem(ODEFunction(rhs; mass_matrix = I), ones(2), (0.0, 1.0))
+            integ = init(prob)
+            u0, _, success = SciMLBase.get_initial_values(
+                prob, integ, prob.f, SciMLBase.CheckInit(),
+                Val(false); abstol = 1e-10
+            )
+            @test success
+            @test u0 == prob.u0
+        end
     end
 
     @testset "DAEProblem" begin

From 211d997a6eb8ce77eac2e2c648c06f90fe1ded0f Mon Sep 17 00:00:00 2001
From: Aayush Sabharwal <aayush.sabharwal@gmail.com>
Date: Fri, 29 Nov 2024 16:10:16 +0530
Subject: [PATCH 2/2] refactor: make spellcheck happy

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

diff --git a/src/problems/nonlinear_problems.jl b/src/problems/nonlinear_problems.jl
index b2a9989c4..b61b19ff1 100644
--- a/src/problems/nonlinear_problems.jl
+++ b/src/problems/nonlinear_problems.jl
@@ -385,7 +385,7 @@ and below.
 !!! warn
     While `explictfuns![i]` could in theory use `sols[i+1]` in its computation,
     these values will not be updated. It is thus the contract of the interface
-    to not use those values except for as caches to be overriden.
+    to not use those values except for as caches to be overridden.
 
 !!! note
     prob.probs[i].p can be aliased with each other as a performance / memory