Implemented FTSwish Activation Function

src/mlpack/methods/ann/layer/ftswish.hpp

@@ -0,0 +1,114 @@
+/**
+ * @file methods/ann/layer/flatten_t_swish.hpp
+ * @author Mayank Raj
+ *
+ * Definition of Flatten T Swish layer first introduced in the acoustic model,
+ * Hock Hung Chieng, Noorhaniza Wahid, Pauline Ong, Sai Raj Kishore Perla,
+ * "Flatten-T Swish: a thresholded ReLU-Swish-like activation function for deep learning", 2018
+ *
+ * mlpack is free software; you may redistribute it and/or modify it under the
+ * terms of the 3-clause BSD license.  You should have received a copy of the
+ * 3-clause BSD license along with mlpack.  If not, see
+ * http://www.opensource.org/licenses/BSD-3-Clause for more information.
+ */
+#ifndef MLPACK_METHODS_ANN_LAYER_FTSWISH_HPP
+#define MLPACK_METHODS_ANN_LAYER_FTSWISH_HPP
+
+#include <mlpack/prereqs.hpp>
+
+#include "layer.hpp"
+
+namespace mlpack {
+
+/**
+ * The Flatten T Swish activation function, defined by
+ *
+ * @f{eqnarray*}{
+ * f'(x) &=& \left\{
+ *   \begin{array}{lr}
+ *     frac{x}{1+exp(-x)} + T & : x \ge 0 \\
+ *     T & : x < 0
+ *   \end{array}
+ * \right. \\
+ * f'(x) &=& \left\{
+ *   \begin{array}{lr}
+ *     \sigma(x)(1 - f(x)) + f(x) & : x > 0 \\
+ *     0 & : x \le 0
+ *   \end{array}
+ * \right.
+ * @f}
+ *
+ * @tparam MatType Matrix representation to accept as input and use for
+ *    computation.
+ */
+template<typename MatType = arma::mat>
+class FTSwishType : public Layer<MatType>
+{
+ public:
+  /**
+   * Create the Flatten T Swish object using the specified parameters.
+   * The thresholded value T can be adjusted via T paramaters.
+   * When the x is < 0, T will be used instead of 0.
+   * The default value of T is -0.20 as suggested in the paper.
+   * @param T 
+   */
+  FTSwishType(const double T = -0.20);
+
+  //! Clone the FTSwishType object. This handles polymorphism correctly.
+  FTSwishType* Clone() const { return new FTSwishType(*this); }
+
+  // Virtual destructor.
+  virtual ~FTSwishType() { }
+
+  //! Copy the given FTSwishType.
+  FTSwishType(const FTSwishType& other);
+  //! Take ownership of the given FTSwishType.
+  FTSwishType(FTSwishType&& other);
+  //! Copy the given FTSwishType.
+  FTSwishType& operator=(const FTSwishType& other);
+  //! Take ownership of the given FTSwishType.
+  FTSwishType& operator=(FTSwishType&& other);
+
+  /**
+   * Ordinary feed forward pass of a neural network, evaluating the function
+   * f(x) by propagating the activity forward through f.
+   *
+   * @param input Input data used for evaluating the specified function.
+   * @param output Resulting output activation.
+   */
+  void Forward(const MatType& input, MatType& output);
+
+  /**
+   * Ordinary feed backward pass of a neural network, calculating the function
+   * f(x) by propagating x backwards through f. Using the results from the feed
+   * forward pass.
+   *
+   * @param input The propagated input activation.
+   * @param gy The backpropagated error.
+   * @param g The calculated gradient.
+   */
+  void Backward(const MatType& input, const MatType& gy, MatType& g);
+
+  //! Get the threshold value.
+  double const& Threshold() const { return T; }
+  //! Modify the threshold value.
+  double& Threshold() { return T; }
+
+  //! Serialize the layer.
+  template<typename Archive>
+  void serialize(Archive& ar, const uint32_t /* version */);
+
+ private:
+  //! Threshold value for x < 0.
+  double T;
+}; // class FTSwishType
+
+// Convenience typedefs.
+typedef FTSwishType<arma::mat> FTSwish;
+
+} // namespace mlpack
+
+// Include implementation.
+#include "ftswish_impl.hpp"
+
+#endif

src/mlpack/methods/ann/layer/ftswish_impl.hpp

@@ -0,0 +1,119 @@
+/**
+ * @file methods/ann/layer/ftswish_impl.hpp
+ * @author Mayank Raj
+ *
+ * Definition of Flatten T Swish layer first introduced in the acoustic model,
+ * Hock Hung Chieng, Noorhaniza Wahid, Pauline Ong, Sai Raj Kishore Perla,
+ * 
+ *
+ * mlpack is free software; you may redistribute it and/or modify it under the
+ * terms of the 3-clause BSD license.  You should have received a copy of the
+ * 3-clause BSD license along with mlpack.  If not, see
+ * http://www.opensource.org/licenses/BSD-3-Clause for more information.
+ */
+#ifndef MLPACK_METHODS_ANN_LAYER_FTSWISH_IMPL_HPP
+#define MLPACK_METHODS_ANN_LAYER_FTSWISH_IMPL_HPP
+
+// In case it hasn't yet been included.
+#include "ftswish.hpp"
+
+namespace mlpack {
+
+template<typename MatType>
+FTSwishType<MatType>::FTSwishType(const double T) :
+    Layer<MatType>(),
+    T(T)
+{
+  // Nothing to do here.
+}
+
+template<typename MatType>
+FTSwishType<MatType>::FTSwishType(const FTSwishType& other) :
+    Layer<MatType>(other),
+    T(other.T)
+{
+  // Nothing to do.
+}
+
+template<typename MatType>
+FTSwishType<MatType>::FTSwishType(FTSwishType&& other) :
+    Layer<MatType>(std::move(other)),
+    T(std::move(other.T))
+{
+  // Nothing to do.
+}
+
+template<typename MatType>
+FTSwishType<MatType>&
+FTSwishType<MatType>::operator=(const FTSwishType& other)
+{
+  if (&other != this)
+  {
+    Layer<MatType>::operator=(other);
+    T = other.T;
+  }
+
+  return *this;
+}
+
+template<typename MatType>
+FTSwishType<MatType>&
+FTSwishType<MatType>::operator=(FTSwishType&& other)
+{
+  if (&other != this)
+  {
+    Layer<MatType>::operator=(std::move(other));
+    T = std::move(other.T);
+  }
+
+  return *this;
+}
+
+template<typename MatType>
+void FTSwishType<MatType>::Forward(const MatType& input, MatType& output)
+{
+  #pragma omp for
+  for (size_t i = 0; i < (size_t) input.n_elem; ++i)
+  {
+    if (input(i) >= 0)
+      output(i) = input(i) / (1 + std::exp(-input(i))) + T;
+    else
+      output(i) = T;
+  }
+}
+
+template<typename MatType>
+void FTSwishType<MatType>::Backward(
+    const MatType& input, const MatType& gy, MatType& g)
+{
+  #pragma omp for
+  for (size_t i = 0; i < (size_t) input.n_elem; ++i)
+  {
+    if (input(i) >= 0)
+    {
+      const double f_x = input(i) / (1 + std::exp(-input(i)));
+      const double sigmoid_x = 1 / (1 + std::exp(-input(i)));
+
+      g(i) = gy(i) * (sigmoid_x * (1 - f_x) + f_x);
+    }
+    else
+    {
+      g(i) = 0;
+    }
+  }
+}
+
+template<typename MatType>
+template<typename Archive>
+void FTSwishType<MatType>::serialize(
+    Archive& ar,
+    const uint32_t /* version */)
+{
+  ar(cereal::base_class<Layer<MatType>>(this));
+
+  ar(CEREAL_NVP(T));
+}
+
+} // namespace mlpack
+
+#endif

src/mlpack/methods/ann/layer/layer_types.hpp

@@ -48,6 +48,7 @@
 #include <mlpack/methods/ann/layer/radial_basis_function.hpp>
 #include <mlpack/methods/ann/layer/softmax.hpp>
 #include <mlpack/methods/ann/layer/softmin.hpp>
+#include <mlpack/methods/ann/layer/ftswish.hpp>
 
 // Convolution modes.
 #include <mlpack/methods/ann/convolution_rules/border_modes.hpp>

src/mlpack/methods/ann/layer/serialization.hpp

@@ -70,6 +70,7 @@
     CEREAL_REGISTER_TYPE(mlpack::SoftmaxType<__VA_ARGS__>); \
     CEREAL_REGISTER_TYPE(mlpack::SoftminType<__VA_ARGS__>); \
     CEREAL_REGISTER_TYPE(mlpack::HardTanHType<__VA_ARGS__>); \
+    CEREAL_REGISTER_TYPE(mlpack::FTSwishType<__VA_ARGS__>); \
 
 CEREAL_REGISTER_MLPACK_LAYERS(arma::mat);
 

src/mlpack/tests/ann/layer/ftswish.cpp

@@ -0,0 +1,62 @@
+/*
+ * @file tests/ann/layer/hard_tanh.cpp
+ * @author Mayank Raj
+ *
+ * Tests the FTSwish layer.
+ *
+ * mlpack is free software; you may redistribute it and/or modify it under the
+ * terms of the 3-clause BSD license.  You should have received a copy of the
+ * 3-clause BSD license along with mlpack.  If not, see
+ * http://www.opensource.org/licenses/BSD-3-Clause for more information.
+ */
+
+#include <mlpack/core.hpp>
+#include <mlpack/methods/ann.hpp>
+
+#include "../../test_catch_tools.hpp"
+#include "../../catch.hpp"
+#include "../../serialization.hpp"
+#include "../ann_test_tools.hpp"
+
+using namespace mlpack;
+
+/**
+ * Simple test case for the FTSwish layer.
+ */
+TEST_CASE("FTSwishTest", "[ANNLayerTest]")
+{
+  // Set the threshold value for the FTSwish layer.
+  double threshold = -0.2;
+
+  // Create the FTSwish layer.
+  FTSwishType<> layer(threshold);
+
+  // Input and output matrices.
+  arma::mat input = {{0.234, 1.23, -1.34},
+    {1.45, 2.001, -0.98},
+    {-3.14, 3.43, 9.9}};
+  arma::mat actualOutput = {{-0.06937312,  0.75179685, -0.2},
+    {0.97449773,  1.56268497, -0.2},
+    {-0.2,  3.1223977, 9.6995033 }};
+  arma::mat output;
+  output.set_size(3,3);
+  // Forward pass.
+  layer.Forward(input, output);
+
+  // Test the Forward function
+  REQUIRE(abs(arma::accu(output - actualOutput)) <= 0.0001);
+
+  arma::mat delta = {{0.0 ,0.84327731, 0.0},
+    {0.91985943, 1.05058055 ,0.0 },
+    {0.0, 1.08399125 ,1.00053333}};
+
+  arma::mat gy, g;
+  gy.set_size(3,3);
+  gy.fill(1);
+  g.set_size(3,3);
+  // Backward pass.
+  layer.Backward(output, gy, g);
+
+  //Test the Backward function
+  REQUIRE(abs(arma::accu(g - delta)) <= 0.0001);
+}

src/mlpack/tests/ann/layer_test.cpp

@@ -37,3 +37,4 @@
 #include "layer/parametric_relu.cpp"
 #include "layer/softmax.cpp"
 #include "layer/softmin.cpp"
+#include "layer/ftswish.cpp"