From 5fe46e69b7363d0b897e1c91d15c1a2d207e7e7a Mon Sep 17 00:00:00 2001
From: Christopher Rackauckas <accounts@chrisrackauckas.com>
Date: Fri, 19 Jul 2024 19:23:04 -0400
Subject: [PATCH] document the fully_determined behavior

---
 docs/src/tutorials/initialization.md     | 9 ++++++++-
 src/systems/diffeqs/abstractodesystem.jl | 4 ++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/docs/src/tutorials/initialization.md b/docs/src/tutorials/initialization.md
index 8af6a512e2..4886a47a73 100644
--- a/docs/src/tutorials/initialization.md
+++ b/docs/src/tutorials/initialization.md
@@ -194,6 +194,13 @@ may not be analytically satisfiable!**. In our case here, if you sit down with a
 long enough you will see that `λ = 0` is required for this equation, but since we chose
 `λ = 1` we end up with a set of equations that are impossible to satisfy.
 
+!!! note
+
+    If you would prefer to have an error instead of a warning in the context of non-fully
+    determined systems, pass the keyword argument `fully_determined = true` into the
+    problem constructor. Additionally, any warning about not being fully determined can
+    be supressed via passing `warn_initialize_determined = false`.
+
 ## Diving Deeper: Constructing the Initialization System
 
 To get a better sense of the initialization system and to help debug it, you can construct
@@ -271,7 +278,7 @@ sol = solve(iprob)
 ```
 
 !!! note
-    
+
     For more information on solving NonlinearProblems and NonlinearLeastSquaresProblems,
     check out the [NonlinearSolve.jl tutorials!](https://docs.sciml.ai/NonlinearSolve/stable/tutorials/getting_started/).
 
diff --git a/src/systems/diffeqs/abstractodesystem.jl b/src/systems/diffeqs/abstractodesystem.jl
index f4268c506a..11abadad5f 100644
--- a/src/systems/diffeqs/abstractodesystem.jl
+++ b/src/systems/diffeqs/abstractodesystem.jl
@@ -1556,10 +1556,10 @@ function InitializationProblem{iip, specialize}(sys::AbstractODESystem,
     nunknown = length(unknowns(isys))
 
     if warn_initialize_determined && neqs > nunknown
-        @warn "Initialization system is overdetermined. $neqs equations for $nunknown unknowns. Initialization will default to using least squares. To suppress this warning pass warn_initialize_determined = false."
+        @warn "Initialization system is overdetermined. $neqs equations for $nunknown unknowns. Initialization will default to using least squares. To suppress this warning pass warn_initialize_determined = false. To make this warning into an error, pass fully_determined = true"
     end
     if warn_initialize_determined && neqs < nunknown
-        @warn "Initialization system is underdetermined. $neqs equations for $nunknown unknowns. Initialization will default to using least squares. To suppress this warning pass warn_initialize_determined = false."
+        @warn "Initialization system is underdetermined. $neqs equations for $nunknown unknowns. Initialization will default to using least squares. To suppress this warning pass warn_initialize_determined = false. To make this warning into an error, pass fully_determined = true"
     end
 
     parammap = parammap isa DiffEqBase.NullParameters || isempty(parammap) ?