add FlattenLayerOp

Author: schillic

docs/src/lib/Architecture.md

@@ -63,6 +63,7 @@ AbstractPoolingLayerOp
 
 ```@docs
 DenseLayerOp
+FlattenLayerOp
 MaxPoolingLayerOp
 MeanPoolingLayerOp
 ```

src/Architecture/Architecture.jl

@@ -9,14 +9,15 @@ using Requires
 using Statistics: mean
 
 export AbstractNeuralNetwork, FeedforwardNetwork,
-       AbstractLayerOp, DenseLayerOp,
+       AbstractLayerOp, DenseLayerOp, FlattenLayerOp,
        AbstractPoolingLayerOp, MaxPoolingLayerOp, MeanPoolingLayerOp,
        layers, dim_in, dim_out,
        ActivationFunction, Id, ReLU, Sigmoid, Tanh, LeakyReLU
 
 include("ActivationFunction.jl")
 include("LayerOps/AbstractLayerOp.jl")
 include("LayerOps/DenseLayerOp.jl")
+include("LayerOps/FlattenLayerOp.jl")
 include("LayerOps/PoolingLayerOp.jl")
 include("NeuralNetworks/AbstractNeuralNetwork.jl")
 include("NeuralNetworks/FeedforwardNetwork.jl")

src/Architecture/LayerOps/FlattenLayerOp.jl

@@ -0,0 +1,44 @@
+"""
+    FlattenLayerOp <: AbstractLayerOp
+
+A flattening layer operation converts a multidimensional tensor into a vector.
+
+### Notes
+
+The implementation uses row-major ordering for convenience with the
+machine-learning literature.
+
+```@jldoctest
+julia> T = reshape([1, 3, 2, 4, 5, 7, 6, 8], (2, 2, 2))
+2×2×2 Array{Int64, 3}:
+[:, :, 1] =
+ 1  2
+ 3  4
+
+[:, :, 2] =
+ 5  6
+ 7  8
+
+julia> FlattenLayerOp()(T)
+8-element Vector{Int64}:
+ 1
+ 2
+ 3
+ 4
+ 5
+ 6
+ 7
+ 8
+```
+"""
+struct FlattenLayerOp <: AbstractLayerOp
+end
+
+# application to a vector (swap to row-major convention)
+function (L::FlattenLayerOp)(T)
+    s = size(T)
+    if length(s) == 1
+        return vec(T)
+    end
+    return vec(permutedims(T, (2, 1, 3:length(s)...)))
+end

test/Architecture/FlattenLayerOp.jl

@@ -0,0 +1,8 @@
+L = FlattenLayerOp()
+
+# output for tensor `T`
+@test L([1 2; 3 4]) == [1, 2, 3, 4]
+@test L([1]) == [1]
+
+# equality
+@test L == FlattenLayerOp()

test/runtests.jl

@@ -16,6 +16,9 @@ struct TestActivation <: ActivationFunction end
     @testset "DenseLayerOp" begin
         include("Architecture/DenseLayerOp.jl")
     end
+    @testset "FlattenLayerOp" begin
+        include("Architecture/FlattenLayerOp.jl")
+    end
     @testset "PoolingLayerOp" begin
         include("Architecture/PoolingLayerOp.jl")
     end