From d03dca7c3b4087a8c3058804bcb05cba4e6626da Mon Sep 17 00:00:00 2001
From: Fredrik Bagge Carlson <baggepinnen@gmail.com>
Date: Tue, 1 Mar 2022 07:41:29 +0100
Subject: [PATCH] add div methods for Dual

---
 src/forwarddiff.jl       | 7 +++++++
 test/test_forwarddiff.jl | 6 +++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/forwarddiff.jl b/src/forwarddiff.jl
index 05e82f09..d1aa714b 100644
--- a/src/forwarddiff.jl
+++ b/src/forwarddiff.jl
@@ -54,6 +54,13 @@ for PT in (Particles, StaticParticles)
             Dual{T}($PT(value(d) .- p.particles), ntuple(i->$PT(0p.particles .+ partials(d)[i]) ,length(partials(d))))
         end
 
+        function Base.:(/)(p::$PT, d::Dual{T}) where {T}
+            Dual{T}($PT(p.particles ./ value(d)), ntuple(i->$PT(0p.particles ./ partials(d)[i]) ,length(partials(d))))
+        end
+        function Base.:(/)(d::Dual{T}, p::$PT) where {T}
+            Dual{T}($PT(value(d) ./ p.particles), ntuple(i->$PT(0p.particles .+ partials(d)[i]) ,length(partials(d))))
+        end
+
         function Base.promote_rule(::Type{ForwardDiff.Dual{T,V,NP}}, ::Type{$PT{S, N}}) where {T, V, NP, S, N}
             VS = promote_type(V,S)
             Dual{T, $PT{VS, N}, NP}
diff --git a/test/test_forwarddiff.jl b/test/test_forwarddiff.jl
index c71c6dd4..9780d967 100644
--- a/test/test_forwarddiff.jl
+++ b/test/test_forwarddiff.jl
@@ -8,7 +8,7 @@ const FD = ForwardDiff
     # In the cost function below, we ensure that $cx+dy > 10 \; ∀ \; c,d ∈ P$ by looking at the worst case
     function cost(params)
         x,y = params
-        -(3x+2y) + 10000sum(params .< 0) + 10000*(pmaximum(c*x+d*y) > 10)
+        -(3x+2y) + 10000sum(params .< 0) + 10000*(pmaximum(c*x+d*y) > 10) + (x/3)*(3/x) - 1
     end
 
     params = [1., 2] # Initial guess
@@ -55,4 +55,8 @@ const FD = ForwardDiff
     @test pmean(pmean(r[2])) != ref[2]
 
     unsafe_comparisons(false)
+
+    x = paramsp[1]
+    @test FD.derivative(x -> x/2, x) == 1/2
+    @test FD.derivative(x -> 2/x, x) ≈ -2/x^2
 end