From fe1402b06faf323af48850235638a4fdf95da130 Mon Sep 17 00:00:00 2001
From: Chris Rackauckas <accounts@chrisrackauckas.com>
Date: Fri, 11 Feb 2022 06:09:33 -0500
Subject: [PATCH] don't fill! on a SparseMatrix
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```julia
julia> x = sprand(2,2,0.5)
2×2 SparseMatrixCSC{Float64, Int64} with 1 stored entry:
 0.507603   ⋅
  ⋅         ⋅

julia> fill!(x, true)
2×2 SparseMatrixCSC{Float64, Int64} with 4 stored entries:
 1.0  1.0
 1.0  1.0
```

Seems like an issue for Base.
---
 src/differentiation/compute_jacobian_ad.jl | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/differentiation/compute_jacobian_ad.jl b/src/differentiation/compute_jacobian_ad.jl
index 0afffe28..d372126b 100644
--- a/src/differentiation/compute_jacobian_ad.jl
+++ b/src/differentiation/compute_jacobian_ad.jl
@@ -296,7 +296,11 @@ function forwarddiff_color_jacobian!(J::AbstractMatrix{<:Number},
     color_i = 1
     maxcolor = maximum(colorvec)
 
-    fill!(J, zero(eltype(J)))
+    if J isa SparseMatrixCSC
+        fill!(nonzeros(J), zero(eltype(J)))
+    else
+        fill!(J, zero(eltype(J)))
+    end
 
     if FiniteDiff._use_findstructralnz(sparsity)
         rows_index, cols_index = ArrayInterface.findstructralnz(sparsity)