consistently use delta for gradients

src/cost.jl

@@ -1,8 +1,8 @@
 export mse, mse!
 
-function mse!(∇, pred, target)
-  map!(-, ∇, pred, target)
-  sumabs2(∇)/2
+function mse!(Δ, pred, target)
+  map!(-, Δ, pred, target)
+  sumabs2(Δ)/2
 end
 
 mse(pred, target) = mse(similar(pred), pred, target)

src/layers/chain.jl

@@ -23,7 +23,7 @@ end
 @forward Chain.layers Base.getindex, Base.first, Base.last
 
 (s::Chain)(x) = foldl((x, m) -> m(x), x, s.layers)
-back!(s::Chain, ∇) = foldr((m, ∇) -> back!(m, ∇), ∇, s.layers)
+back!(s::Chain, Δ) = foldr((m, Δ) -> back!(m, Δ), Δ, s.layers)
 update!(s::Chain, η) = foreach(l -> update!(l, η), s.layers)
 
 graph(s::Chain) =

src/layers/shape.jl

@@ -23,7 +23,7 @@ end
 Input(i...) = Input(dims(i...))
 
 (::Input)(x) = x
-back!(::Input, ∇, x) = ∇
+back!(::Input, Δ, x) = Δ
 
 # Initialise placeholder
 

src/model.jl

@@ -4,7 +4,7 @@ export Model, back!, update!, param
 
 abstract Model
 
-back!(m::Model, ∇) = error("Backprop not implemented for $(typeof(m))")
+back!(m::Model, Δ) = error("Backprop not implemented for $(typeof(m))")
 update!(m, η) = m
 
 graph(m) = nothing

src/utils.jl

@@ -6,14 +6,14 @@ initn(dims...) = randn(Float32, dims...)/10
 
 function train!(m, train, test = []; epoch = 1, batch = 10, η = 0.1)
     i = 0
-    ∇ = zeros(length(train[1][2]))
+    Δ = zeros(length(train[1][2]))
     for _ in 1:epoch
       @progress for (x, y) in train
         i += 1
         pred = m(x)
         any(isnan, pred) && error("NaN")
-        err = mse!(∇, pred, y)
-        back!(m, ∇, x)
+        err = mse!(Δ, pred, y)
+        back!(m, Δ, x)
         i % batch == 0 && update!(m, η)
         i % 1000 == 0 && @show accuracy(m, test)
       end