Merge pull request #666 from JuliaDiff/ox/div

add scaling division

Author: oxinabox

src/tangent_types/abstract_tangent.jl

@@ -38,3 +38,6 @@ abstract type AbstractTangent end
 Base.:+(x::AbstractTangent) = x
 
 @inline Base.conj(x::AbstractTangent) = x
+
+Base.:/(x::AbstractTangent, y) = x * inv(y)
+Base.:\(x, y::AbstractTangent) = inv(x) * y

test/tangent_types/structural_tangent.jl

@@ -396,6 +396,16 @@ end
             @test_throws MethodError Tangent{Foo}(; y=1.5, x=2.5) * @thunk [1 2; 3 4]
         end
 
+        @testset "scaling division" begin
+            a = Tangent{Foo}(; x=2.0, y=-2.0)
+            @test a / 2.0 == Tangent{Foo}(; x=1.0, y=-1.0) == 2.0 \ a
+            @test (
+                Tangent{Tuple{Float64,Float64}}(2.0, 4.0) / 2.0 ==
+                Tangent{Tuple{Float64,Float64}}(1.0, 2.0) ==
+                2.0 \ Tangent{Tuple{Float64,Float64}}(2.0, 4.0)
+            )
+        end
+
         @testset "iszero" begin
             @test iszero(Tangent{Foo}())
             @test iszero(Tangent{Tuple{}}())