fix: add RecursiveArrayToolsReverseDiffExt

Author: AayushSabharwal

Project.toml

@@ -23,11 +23,13 @@ Measurements = "eff96d63-e80a-5855-80a2-b1b0885c5ab7"
 MonteCarloMeasurements = "0987c9cc-fe09-11e8-30f0-b96dd679fdca"
 Tracker = "9f7883ad-71c0-57eb-9f7f-b5c9e6d3789c"
 Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
+ReverseDiff = "37e2e3b7-166d-5795-8a7a-e32c996b4267"
 
 [extensions]
 RecursiveArrayToolsFastBroadcastExt = "FastBroadcast"
 RecursiveArrayToolsMeasurementsExt = "Measurements"
 RecursiveArrayToolsMonteCarloMeasurementsExt = "MonteCarloMeasurements"
+RecursiveArrayToolsReverseDiffExt = ["ReverseDiff", "Zygote"]
 RecursiveArrayToolsTrackerExt = "Tracker"
 RecursiveArrayToolsZygoteExt = "Zygote"
 
@@ -49,6 +51,7 @@ OrdinaryDiffEq = "6.62"
 Pkg = "1"
 Random = "1"
 RecipesBase = "1.1"
+ReverseDiff = "1.15"
 SafeTestsets = "0.1"
 SparseArrays = "1.10"
 StaticArrays = "1.6"

ext/RecursiveArrayToolsReverseDiffExt.jl

@@ -0,0 +1,17 @@
+module RecursiveArrayToolsReverseDiffExt
+
+using RecursiveArrayTools
+using ReverseDiff
+using Zygote: @adjoint
+
+@adjoint function Array(VA::AbstractVectorOfArray{<:ReverseDiff.TrackedReal})
+    function Array_adjoint(y)
+        VA = recursivecopy(VA)
+        for (i, slice) in zip(eachindex(VA.u), eachslice(y, dims=ndims(y)))
+            VA.u[i] = reshape(reduce(vcat, slice), size(VA.u[i]))
+        end
+        return (VA,)
+    end
+    return Array(VA), Array_adjoint
+end
+end # module