From 9a2f7bbec515c55e5594feef7928670cb811169c Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <51025924+simsurace@users.noreply.github.com>
Date: Mon, 20 Nov 2023 13:53:06 +0100
Subject: [PATCH] Remove chainrule and test for `SqMahalanobis` (#539)

---
 Project.toml       |  2 +-
 src/chainrules.jl  | 22 ----------------------
 test/chainrules.jl |  9 ---------
 3 files changed, 1 insertion(+), 32 deletions(-)

diff --git a/Project.toml b/Project.toml
index 19247efdf..c46c5c334 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "KernelFunctions"
 uuid = "ec8451be-7e33-11e9-00cf-bbf324bd1392"
-version = "0.10.59"
+version = "0.10.60"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
diff --git a/src/chainrules.jl b/src/chainrules.jl
index eebdf95b5..d31ec97d1 100644
--- a/src/chainrules.jl
+++ b/src/chainrules.jl
@@ -121,28 +121,6 @@ function ChainRulesCore.rrule(s::Sinus, x::AbstractVector, y::AbstractVector)
     return val, evaluate_pullback
 end
 
-## Reverse Rules SqMahalanobis
-
-function ChainRulesCore.rrule(
-    dist::Distances.SqMahalanobis, a::AbstractVector, b::AbstractVector
-)
-    d = dist(a, b)
-    function SqMahalanobis_pullback(Δ::Real)
-        a_b = a - b
-        ∂qmat = InplaceableThunk(
-            X̄ -> mul!(X̄, a_b, a_b', true, Δ), @thunk((a_b * a_b') * Δ)
-        )
-        ∂a = InplaceableThunk(
-            X̄ -> mul!(X̄, dist.qmat, a_b, true, 2 * Δ), @thunk((2 * Δ) * dist.qmat * a_b)
-        )
-        ∂b = InplaceableThunk(
-            X̄ -> mul!(X̄, dist.qmat, a_b, true, -2 * Δ), @thunk((-2 * Δ) * dist.qmat * a_b)
-        )
-        return Tangent{typeof(dist)}(; qmat=∂qmat), ∂a, ∂b
-    end
-    return d, SqMahalanobis_pullback
-end
-
 ## Reverse Rules for matrix wrappers
 
 function ChainRulesCore.rrule(::Type{<:ColVecs}, X::AbstractMatrix)
diff --git a/test/chainrules.jl b/test/chainrules.jl
index 03c2c3b1f..5c3c5766b 100644
--- a/test/chainrules.jl
+++ b/test/chainrules.jl
@@ -3,8 +3,6 @@
     x = rand(rng, 5)
     y = rand(rng, 5)
     r = rand(rng, 5)
-    Q = Matrix(Cholesky(rand(rng, 5, 5), 'U', 0))
-    @assert isposdef(Q)
 
     compare_gradient(:Zygote, [x, y]) do xy
         Euclidean()(xy[1], xy[2])
@@ -21,11 +19,4 @@
     compare_gradient(:Zygote, [x, y]) do xy
         KernelFunctions.Sinus(r)(xy[1], xy[2])
     end
-    if VERSION < v"1.6"
-        @test_broken "Chain rule of SqMahalanobis is broken in Julia pre-1.6"
-    else
-        compare_gradient(:Zygote, [Q, x, y]) do Qxy
-            SqMahalanobis(Qxy[1])(Qxy[2], Qxy[3])
-        end
-    end
 end