Recursive Auto-Encoder

May 20, 2023

The Recursive Auto-Encoder (RAE) is a deep learning technique used in natural language processing (NLP) that aims to learn a hierarchical representation of texts.


Text data is inherently high-dimensional and can be difficult to process. Traditional methods of NLP relied on hand-crafted features and shallow learning algorithms, which often resulted in limited accuracy and scalability. With the advent of deep learning techniques, however, researchers have been able to develop more advanced models capable of processing large amounts of text data.

The RAE is one such model, developed by Richard Socher and his team at Stanford University in 2011. It is a neural network that learns a hierarchical representation of texts by recursively encoding and decoding sentences.

How it works

The RAE consists of two main parts: the encoder and the decoder. The encoder takes in a sentence and produces a hidden representation, while the decoder takes in the hidden representation and reconstructs the original sentence.

The RAE is trained in a recursive manner, with each iteration of encoding and decoding resulting in a lower-dimensional representation of the text. This process continues until the final representation is obtained.

One unique aspect of the RAE is its use of a binary tree structure to encode texts. Each sentence is represented as a leaf node in the tree, with the internal nodes representing progressively higher-level abstractions.


The RAE has several benefits over traditional NLP techniques. Firstly, it is able to learn a hierarchical representation of texts, which allows for more nuanced and accurate analysis. Secondly, it is able to process large amounts of data quickly and efficiently, making it suitable for use in large-scale applications. Additionally, the RAE is able to handle variable-length inputs, which is particularly useful in NLP applications where texts can vary greatly in length.


The RAE has been used in a variety of NLP applications, including sentiment analysis, text classification, and machine translation. One example of its use is in the analysis of customer feedback for businesses. By using the RAE to analyze customer reviews, businesses can gain insights into the strengths and weaknesses of their products and services.

Code Example

Here is an example of how to implement a simple RAE using the PyTorch framework:

import torch
import torch.nn as nn

class RAE(nn.Module):
    def __init__(self, vocab_size, emb_dim, hidden_dim):
        super(RAE, self).__init__()
        self.encoder = nn.Linear(vocab_size, hidden_dim)
        self.decoder = nn.Linear(hidden_dim, vocab_size)
        self.activation = nn.Sigmoid()

    def forward(self, x):
        x = self.encoder(x)
        x = self.activation(x)
        x = self.decoder(x)
        x = self.activation(x)
        return x

This code defines a basic RAE model with an encoder, decoder, and sigmoid activation function. The vocab_size, emb_dim, and hidden_dim parameters are used to define the size of the input, embedding, and hidden layers, respectively.