com.kotlinnlp.simplednn.deeplearning.treernn.TreeRNN.kt Maven / Gradle / Ivy

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/* Copyright 2016-present The KotlinNLP Authors. All Rights Reserved.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, you can obtain one at http://mozilla.org/MPL/2.0/.
 * ------------------------------------------------------------------*/

package com.kotlinnlp.simplednn.deeplearning.treernn

import com.kotlinnlp.simplednn.core.functionalities.activations.Tanh
import com.kotlinnlp.simplednn.core.functionalities.initializers.GlorotInitializer
import com.kotlinnlp.simplednn.core.functionalities.initializers.Initializer
import com.kotlinnlp.simplednn.core.layers.LayerConfiguration
import com.kotlinnlp.simplednn.core.layers.LayerType
import com.kotlinnlp.simplednn.core.neuralnetwork.NeuralNetwork
import java.io.Serializable

/**
 * The TreeRNN treats the children of a node as a sequence, and encode this sequence using
 * an RNN. The left-children and right-children are encoded using two separate RNNs:
 * the first RNN [leftRNN] encodes the sequence of left-children from the head outwards,
 * and the second RNN [rightRNN] the sequence of right-children from the head outwards.
 *
 * The output of the [leftRNN] and the [rightRNN] are concatenated, then the [concatNetwork]
 * is used to reduced the output back to d-dimensions using a linear transformation
 * followed by the non-linear activation function. This means that the TreeRNN output layer
 * has the same size of the input layer.
 *
 * Note: the number of recurrent layers of the TreeRNN is fixed to one.
 *
 * @property inputLayerSize size of the input layer
 * @property hiddenLayerSize size of the hidden layer
 * @property hiddenLayerConnectionType type of the recurrent layer
 * @param weightsInitializer the initializer of the weights (zeros if null, default: Glorot)
 * @param biasesInitializer the initializer of the biases (zeros if null, default: Glorot)
 */
class TreeRNN(
  val inputLayerSize: Int,
  val hiddenLayerSize: Int,
  val hiddenLayerConnectionType: LayerType.Connection = LayerType.Connection.GRU,
  weightsInitializer: Initializer? = GlorotInitializer(),
  biasesInitializer: Initializer? = GlorotInitializer()
) : Serializable {

  companion object {

    /**
     * Private val used to serialize the class (needed from Serializable).
     */
    @Suppress("unused")
    private const val serialVersionUID: Long = 1L
  }

  /**
   * The size of the output layer
   */
  val outputLayerSize: Int = this.inputLayerSize

  /**
   * The Recurrent Neural Network to encode the left-children sequence
   */
  val leftRNN = NeuralNetwork(
    LayerConfiguration(size = this.inputLayerSize),
    LayerConfiguration(size = this.hiddenLayerSize,
      activationFunction = Tanh(), // fixed
      connectionType = this.hiddenLayerConnectionType),
    weightsInitializer = weightsInitializer,
    biasesInitializer = biasesInitializer
  )

  /**
   * The Recurrent Neural Network to encode the right-children sequence
   */
  val rightRNN = NeuralNetwork(
    LayerConfiguration(size = this.inputLayerSize),
    LayerConfiguration(size = this.hiddenLayerSize,
      activationFunction = Tanh(), // fixed
      connectionType = this.hiddenLayerConnectionType),
    weightsInitializer = weightsInitializer,
    biasesInitializer = biasesInitializer
  )

  /**
   *  The output of the [leftRNN] and the [rightRNN] are concatenated, resulting in a 2d-dimensional vector,
   *  then the [concatNetwork] is used to reduced the output back to d-dimensions using a linear transformation
   *  followed by the non-linear activation function.
   */
  val concatNetwork = NeuralNetwork(
    LayerConfiguration(size = this.hiddenLayerSize * 2),
    LayerConfiguration(size = this.outputLayerSize,
      activationFunction = Tanh(), // fixed
      connectionType = LayerType.Connection.Feedforward),
    weightsInitializer = weightsInitializer,
    biasesInitializer = biasesInitializer
  )

  /**
   * The model of this [TreeRNN] containing its parameters.
   */
  val model = TreeRNNParameters(
    leftRNN = this.leftRNN.model,
    rightRNN = this.rightRNN.model,
    concatNetwork = this.concatNetwork.model
  )

  /**
   * Check hidden layer connection type.
   */
  init {
    require(hiddenLayerConnectionType.property == LayerType.Property.Recurrent) {
      "required hiddenLayerConnectionType with Recurrent property"
    }
  }
}