Add `TrackedArray` support for `repeat(x; inner, outer)`

src/tracker/array.jl

@@ -93,6 +93,26 @@ function back(::typeof(repmat), Δ, xs::TrackedVecOrMat, m, n=1)
     back(xs, Δ′)
 end
 
+
+_repeat(A, inner, outer) = Base.repeat(A; inner=inner, outer=outer)
+Base.repeat(A::TrackedArray; inner=ntuple(x->1, ndims(A)), outer=ntuple(x->1, ndims(A))) = track(_repeat, A, inner, outer)
+
+function back(::typeof(_repeat), Δ, xs::TrackedArray, inner, outer)
+    Δ′ = similar(xs.data)
+    Δ′ .= 0
+    S = size(xs.data)
+    
+    # Loop through each element of Δ, calculate source dimensions, accumulate into Δ′
+    for (dest_idx, val) in enumerate(IndexCartesian(), Δ)
+        # First, round dest_idx[dim] to nearest gridpoint defined by inner[dim], then
+        # wrap around based on original size S.
+        src_idx = [mod1(div(dest_idx[dim] - 1, inner[dim]) + 1, S[dim]) for dim in 1:length(S)]
+        Δ′[src_idx...] += val
+    end
+    back(xs, Δ′)
+end
+
+
 for f in [:vcat, :hcat]
   @eval begin
     # This section is a bit of a hack since julia doesn't have a standardised

test/tracker.jl

@@ -114,6 +114,9 @@ end
 @test gradtest(x -> repmat(x, 5,5), rand(4,5))
 @test gradtest(x -> repmat(x, 5), rand(4,5))
 
+@test gradtest(x -> repeat(x; inner=2, outer=3), rand(5))
+@test gradtest(x -> repeat(x; inner=(2,2,1), outer=(1,1,3)), rand(5,4,3))
+
 @test gradtest(kron, rand(5), rand(3))
 @test gradtest(kron, rand(5), rand(3), rand(8))
 @test gradtest(kron, rand(5,1), rand(3,1))