From 2b0f965f15ed1691d34d02f421f10bac6d25ab10 Mon Sep 17 00:00:00 2001
From: Phillip Alday <me@phillipalday.com>
Date: Mon, 25 Aug 2025 11:48:49 +0200
Subject: [PATCH] provide a breadcrumb when spline interpolation fails during
 profiling

---
 issues/794/Project.toml |  5 +++++
 issues/794/main.jl      | 13 +++++++++++++
 src/profile/sigmapr.jl  | 11 +++++++++--
 src/profile/vcpr.jl     | 11 ++++++++---
 4 files changed, 35 insertions(+), 5 deletions(-)
 create mode 100644 issues/794/Project.toml
 create mode 100644 issues/794/main.jl

diff --git a/issues/794/Project.toml b/issues/794/Project.toml
new file mode 100644
index 000000000..a7ca96922
--- /dev/null
+++ b/issues/794/Project.toml
@@ -0,0 +1,5 @@
+[deps]
+BSplineKit = "093aae92-e908-43d7-9660-e50ee39d5a0a"
+CSV = "336ed68f-0bac-5ca0-87d4-7b16caf5d00b"
+MixedModels = "ff71e718-51f3-5ec2-a782-8ffcbfa3c316"
+MixedModelsDatasets = "7e9fb7ac-9f67-43bf-b2c8-96ba0796cbb6"
diff --git a/issues/794/main.jl b/issues/794/main.jl
new file mode 100644
index 000000000..9c074931d
--- /dev/null
+++ b/issues/794/main.jl
@@ -0,0 +1,13 @@
+using CSV
+using MixedModels
+using MixedModelsDatasets: dataset
+x = CSV.read(download("https://gist.githubusercontent.com/yjunechoe/af4a8dd3e2b0343fe3818e93dba8c81d/raw/x.csv"), Table);
+m = fit(MixedModel, @formula(y ~ x1 * x2 + (1 | g)), x)
+
+profile(m; threshold=4) # works
+
+profile(m; threshold=3)
+
+s = lmm(@formula(reaction ~ 1 + days + (1 + days| subj)), dataset(:sleepstudy))
+
+profile(s; threshold=3)
diff --git a/src/profile/sigmapr.jl b/src/profile/sigmapr.jl
index 3336ebe52..186cb5051 100644
--- a/src/profile/sigmapr.jl
+++ b/src/profile/sigmapr.jl
@@ -33,6 +33,7 @@ end
     profileσ(m::LinearMixedModel, tc::TableColumns; threshold=4)
 
 Return a Table of the profile of `σ` for model `m`.  The profile extends to where the magnitude of ζ exceeds `threshold`.
+
 !!! note
     This method is called by `profile` and currently considered internal.
     As such, it may change or disappear in a future release without being considered breaking.
@@ -69,7 +70,13 @@ function profileσ(m::LinearMixedModel{T}, tc::TableColumns{T}; threshold=4) whe
     updateL!(setθ!(m, θ))
     σv = [r.σ for r in tbl]
     ζv = [r.ζ for r in tbl]
-    fwd = Dict(:σ => interpolate(σv, ζv, BSplineOrder(4), Natural()))
-    rev = Dict(:σ => interpolate(ζv, σv, BSplineOrder(4), Natural()))
+    local fwd, rev
+    try
+        fwd = Dict(:σ => interpolate(σv, ζv, BSplineOrder(4), Natural()))
+        rev = Dict(:σ => interpolate(ζv, σv, BSplineOrder(4), Natural()))
+    catch
+        @error "An error occurred while fitting the profile splines for σ. Try adjusting the threshold."
+        rethrow()
+    end
     return (; m, tbl, fwd, rev)
 end
diff --git a/src/profile/vcpr.jl b/src/profile/vcpr.jl
index fca28ef55..e20b09c80 100644
--- a/src/profile/vcpr.jl
+++ b/src/profile/vcpr.jl
@@ -78,9 +78,14 @@ function profileσs!(val::NamedTuple, tc::TableColumns{T}; nzlb=1.0e-8) where {T
             append!(val.tbl, tbl)
             ζcol = getproperty(:ζ).(tbl)
             symcol = gpsym.(tbl)
-            val.fwd[sym] = interpolate(symcol, ζcol, BSplineOrder(4), Natural())
-            issorted(ζcol) &&
-                (val.rev[sym] = interpolate(ζcol, symcol, BSplineOrder(4), Natural()))
+            try
+                val.fwd[sym] = interpolate(symcol, ζcol, BSplineOrder(4), Natural())
+                issorted(ζcol) &&
+                    (val.rev[sym] = interpolate(ζcol, symcol, BSplineOrder(4), Natural()))
+            catch
+                @error "An error occurred while fitting the profile splines for the variance components. Try adjusting the threshold."
+                rethrow()
+            end
         end
     end
     copyto!(final, initial)