Add Separable Conv2D Layer. (#362)

Author: Shashi456

Sources/TensorFlow/Layers/Convolutional.swift

@@ -138,7 +138,7 @@ public struct Conv2D<Scalar: TensorFlowFloatingPoint>: Layer {
     @noDerivative public let padding: Padding
     /// The dilation factor for spatial dimensions.
     @noDerivative public let dilations: (Int, Int)
-    
+
     /// The element-wise activation function type.
     public typealias Activation = @differentiable (Tensor<Scalar>) -> Tensor<Scalar>
 
@@ -470,7 +470,7 @@ public struct DepthwiseConv2D<Scalar: TensorFlowFloatingPoint>: Layer {
     /// The element-wise activation function type.
     public typealias Activation = @differentiable (Tensor<Scalar>) -> Tensor<Scalar>
 
-    /// Creates a `DepthwiseConv2D` layer with the specified filter, bias, activation function, 
+    /// Creates a `DepthwiseConv2D` layer with the specified filter, bias, activation function,
     /// strides, and padding.
     ///
     /// - Parameters:
@@ -631,3 +631,111 @@ public struct ZeroPadding3D<Scalar: TensorFlowFloatingPoint>: ParameterlessLayer
         return input.padded(forSizes: [padding.0, padding.1, padding.2])
     }
 }
+
+/// A 2-D Separable convolution layer.
+///
+/// This layer performs a depthwise convolution that acts separately on channels followed by
+/// a pointwise convolution that mixes channels.
+@frozen
+public struct SeparableConv2D<Scalar: TensorFlowFloatingPoint>: Layer {
+    /// The 4-D depthwise convolution kernel.
+    public var depthwiseFilter: Tensor<Scalar>
+    /// The 4-D pointwise convolution kernel.
+    public var pointwiseFilter: Tensor<Scalar>
+    /// The bias vector.
+    public var bias: Tensor<Scalar>
+    /// The element-wise activation function.
+    @noDerivative public let activation: Activation
+    /// The strides of the sliding window for spatial dimensions.
+    @noDerivative public let strides: (Int, Int)
+    /// The padding algorithm for convolution.
+    @noDerivative public let padding: Padding
+
+    /// The element-wise activation function type.
+    public typealias Activation = @differentiable (Tensor<Scalar>) -> Tensor<Scalar>
+
+    /// Creates a `SeparableConv2D` layer with the specified depthwise and pointwise filter,
+    /// bias, activation function, strides, and padding.
+    ///
+    /// - Parameters:
+    ///   - depthwiseFilter: The 4-D depthwise convolution kernel
+    ///     `[filter height, filter width, input channels count, channel multiplier]`.
+    ///   - pointwiseFilter: The 4-D pointwise convolution kernel
+    ///     `[1, 1, channel multiplier * input channels count, output channels count]`.
+    ///   - bias: The bias vector.
+    ///   - activation: The element-wise activation function.
+    ///   - strides: The strides of the sliding window for spatial dimensions.
+    ///   - padding: The padding algorithm for convolution.
+    public init(
+        depthwiseFilter: Tensor<Scalar>,
+        pointwiseFilter: Tensor<Scalar>,
+        bias: Tensor<Scalar>,
+        activation: @escaping Activation = identity,
+        strides: (Int, Int) = (1, 1),
+        padding: Padding = .valid
+    ) {
+        self.depthwiseFilter = depthwiseFilter
+        self.pointwiseFilter = pointwiseFilter
+        self.bias = bias
+        self.activation = activation
+        self.strides = strides
+        self.padding = padding
+    }
+
+    /// Returns the output obtained from applying the layer to the given input.
+    ///
+    /// - Parameter input: The input to the layer.
+    /// - Returns: The output.
+    @differentiable
+    public func callAsFunction(_ input: Tensor<Scalar>) -> Tensor<Scalar> {
+        let depthwise = depthwiseConv2D(
+            input,
+            filter: depthwiseFilter,
+            strides: (1, strides.0, strides.1, 1),
+            padding: padding)
+        return activation(conv2D(
+            depthwise,
+            filter: pointwiseFilter,
+            strides: (1, 1, 1, 1),
+            padding: padding,
+            dilations: (1, 1, 1, 1)) + bias)
+    }
+}
+
+public extension SeparableConv2D {
+    /// Creates a `SeparableConv2D` layer with the specified depthwise and pointwise filter shape,
+    /// strides, padding, and element-wise activation function.
+    ///
+    /// - Parameters:
+    ///   - depthwiseFilterShape: The shape of the 4-D depthwise convolution kernel.
+    ///   - pointwiseFilterShape: The shape of the 4-D pointwise convolution kernel.
+    ///   - strides: The strides of the sliding window for spatial/spatio-temporal dimensions.
+    ///   - padding: The padding algorithm for convolution.
+    ///   - activation: The element-wise activation function.
+    ///   - filterInitializer: Initializer to use for the filter parameters.
+    ///   - biasInitializer: Initializer to use for the bias parameters.
+    init(
+        depthwiseFilterShape: (Int, Int, Int, Int),
+        pointwiseFilterShape: (Int, Int, Int, Int),
+        strides: (Int, Int) = (1, 1),
+        padding: Padding = .valid,
+        activation: @escaping Activation = identity,
+        depthwiseFilterInitializer: ParameterInitializer<Scalar> = glorotUniform(),
+        pointwiseFilterInitializer: ParameterInitializer<Scalar> = glorotUniform(),
+        biasInitializer: ParameterInitializer<Scalar> = zeros()
+    ) {
+        let depthwiseFilterTensorShape = TensorShape([
+            depthwiseFilterShape.0, depthwiseFilterShape.1, depthwiseFilterShape.2,
+            depthwiseFilterShape.3])
+        let pointwiseFilterTensorShape = TensorShape([
+            pointwiseFilterShape.0, pointwiseFilterShape.1, pointwiseFilterShape.2,
+            pointwiseFilterShape.3])
+        self.init(
+            depthwiseFilter: depthwiseFilterInitializer(depthwiseFilterTensorShape),
+            pointwiseFilter: pointwiseFilterInitializer(pointwiseFilterTensorShape),
+            bias: biasInitializer([pointwiseFilterShape.3]),
+            activation: activation,
+            strides: strides,
+            padding: padding)
+    }
+}

Tests/TensorFlowTests/LayerTests.swift

@@ -164,6 +164,24 @@ final class LayerTests: XCTestCase {
         XCTAssertEqual(output, expected)
     }
 
+    func testSeparableConv2D() {
+        let depthwiseFilter =  Tensor(shape: [2, 2, 2, 2], scalars: (0..<16).map(Float.init))
+        let pointwiseFilter =  Tensor(shape: [1, 1, 4, 1], scalars: (0..<4).map(Float.init))
+        let bias = Tensor<Float>([4])
+        let layer = SeparableConv2D<Float>(depthwiseFilter: depthwiseFilter,
+                                           pointwiseFilter: pointwiseFilter,
+                                           bias: bias,
+                                           activation: identity,
+                                           strides: (2, 2),
+                                           padding: .valid)
+        let input = Tensor(shape: [2, 2, 2, 2], scalars: (0..<16).map(Float.init))
+        let output = layer.inferring(from: input)
+        let expected = Tensor<Float>(shape: [2, 1, 1, 1],
+                                     scalars: [1016, 2616])
+        XCTAssertEqual(output, expected)
+    }
+
+
     func testZeroPadding1D() {
         let input = Tensor<Float>([0.0, 1.0, 2.0])
         let layer = ZeroPadding1D<Float>(padding: 2)
@@ -538,6 +556,7 @@ final class LayerTests: XCTestCase {
         ("testConv2DDilation", testConv2DDilation),
         ("testConv3D", testConv3D),
         ("testDepthConv2D", testDepthConv2D),
+        ("testSeparableConv2D", testSeparableConv2D),
         ("testZeroPadding1D", testZeroPadding1D),
         ("testZeroPadding2D", testZeroPadding2D),
         ("testZeroPadding3D", testZeroPadding3D),