Long Short-Term Memory, Structure, Working, Advantages & Disadvantages

Last updated by on Aug 30, 2024 at 08:38 PM | Reading time: 7 minutes

What is LSTM?

Now, let us define 'What is LSTM?' Long short-term memory networks, or LSTMs, are employed in the field of deep learning. It is a subset of recurrent neural networks (RNNs) that may learn long-term relationships, particularly in sequence prediction tasks.

LSTM contains feedback connections, which means it can analyze a whole sequence of data, as opposed to individual data points such as photos.

This has applications in speech recognition, machine translation, and so forth. LSTM is a type of RNN that performs exceptionally well across a wide range of issues.

https://www.youtube.com/watch?v=ggwnI1nyuCg

The Logic behind LSTM

The essential component of an LSTM model is a memory cell known as a 'cell state' which effectively preserves information throughout processing. It can be thought of as a conveyor belt across which information just travels, unmodified, ensuring that essential data is retained and irrelevant details are discarded

In LSTM, gates control the addition and removal of information from the cell state. These gates optionally allow information to move in and out of the cell. It includes an operation for pointwise multiplication and a sigmoid neural network layer to aid the procedure.

The sigmoid layer outputs integers ranging from zero to one, where zero implies 'nothing should be let through' and one indicates 'everything should be let through.

What is an RNN?

Recurrent Neural Networks (RNNs) are a form of neural network designed to analyze sequential data. They can examine data with a temporal component, such as time series, voice, or text. RNNs can accomplish this by transferring a hidden state from one timestep to the next.

The hidden state is updated at each timestep using the input and the previous hidden state. RNNs can capture short-term correlations in sequential data but struggle to catch long-term dependencies.

LSTM vs RNN

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Consider the difficulty of changing specific information in a calendar. To accomplish this, an RNN applies a function to the existing data, entirely changing it. In contrast, LSTM makes minor changes to the data through simple addition or multiplication as it moves through cell states.

This is how LSTM forgets and remembers things selectively, giving it an advantage over RNNs.

Consider that you wish to process data with periodic patterns, such as anticipating colored powder sales that surge during Holi in India. An excellent method is to review the prior year's sales records.

So you must understand what data should be deleted and what should be saved for future reference. Otherwise, you'll need to have an excellent memory.

In theory, recurrent neural networks appear to do well in this regard. However, they have two drawbacks: inflating gradient and disappearing gradient, which render them unnecessary.

Structure of LSTM

The Long Short-Term Memory (LSTM) network is a type of recurrent neural network (RNN) architecture designed to address the vanishing gradient problem in traditional RNNs.

LSTM cells are composed of several key components, including gates and memory states, which enable them to effectively capture long-range dependencies in sequential data.

1) Forget Gate:

The forget gate is responsible for determining which cell states are no longer necessary and can be forgotten.

2) Input Gate:

The input gate determines which new information from the current input should be added to the cell state.
It consists of two components: the input gate and the candidate cell state.
The input gate takes both the current input and the previous hidden state as inputs and produces an input gate activation vector.

3) Candidate Cell State:

The candidate cell state represents the new information that is proposed to be added to the cell state.
It is computed using a tanh activation function applied to the linear combination of the current input and the previous hidden state.
The candidate cell state provides a way for the LSTM cell to update its memory with new information while preserving the existing information stored in the cell state.

4) Update Cell State:

The cell state Ct is updated by combining the information retained from the previous time step with the new information proposed by the candidate cell state.
It is computed by element-wise multiplication of the forget gate activation vector with the previous cell state, and element-wise addition of the input gate activation vector with the scaled candidate cell state.

5) Output Gate:

The output gate determines which information from the current cell state Ct should be passed on to the next hidden state.
It takes both the current input and the previous hidden state as inputs and produces an output gate activation vector.

Working of Long Short-Term Memory

The working of LSTM involves several key components and processes, which enable it to effectively process and remember sequential information. Let's explore the working of LSTM in detail:

1) Gates: As we discussed in the structure, it includes gates - Forget, Input, and Ouput..

2) Cell State:

The cell state represents the "memory" of the LSTM network and is updated over time based on the input and gate activations.

It carries information from previous time steps and is selectively updated by the forget gate and input gate.

3) Hidden State‍

The hidden state captures the short-term memory of the LSTM network and is updated based on the current input and the cell state. It carries information that is relevant for the current time step and is passed on to the next time step.

4) Training:

During training, the LSTM network learns to adjust the parameters (weights and biases) of its gates and cell state to minimize the difference between its predictions and the ground truth labels.

5) Inference:

During inference or prediction, the LSTM network takes in new input sequences and generates predictions based on its learned parameters.

It processes each input sequence step by step, updating its hidden state and cell state at each time step, and producing output predictions based on the final hidden state.

Advantages and Disadvantages of LSTM

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Long Short-Term Memory (LSTM) networks offer several advantages and disadvantages, which influence their suitability for various applications in machine learning and deep learning. Let's explore these factors in detail:

Advantages of LSTM:

Long-Term Dependency Learning: LSTM networks are designed to capture long-range dependencies in sequential data. They can effectively remember information over extended periods.
Handling Vanishing Gradient Problem: Unlike traditional recurrent neural networks (RNNs), LSTM networks mitigate the vanishing gradient problem by introducing specialized gating mechanisms. These gates control the flow of information and gradients, allowing LSTMs to learn and retain information over many time steps without suffering from gradient decay.
Selective Memory Retention: The forget gate in LSTM cells enables selective memory retention by determining which information from the previous time step should be forgotten and which information should be retained.

This mechanism helps prevent the network from becoming overwhelmed by irrelevant information and improves its ability to focus on relevant features.

Robustness to Sequence Length: LSTM networks are capable of processing sequences of varying lengths. Unlike fixed-size input architectures, LSTMs can dynamically adapt to sequences of different lengths, making them flexible and robust in handling input data with variable temporal dynamics.
Parallelism in Training: LSTM networks can be trained efficiently using parallel computing architectures, such as graphics processing units (GPUs) and tensor processing units (TPUs). This parallelism accelerates the training process, allowing researchers and practitioners to train larger and more complex models within a reasonable time frame.

Disadvantages of LSTM:

Complexity and Computational Cost: LSTM networks are more complex than traditional RNN architectures due to their additional gating mechanisms.

This complexity increases the computational cost of training and inference, requiring more computational resources and memory compared to simpler models.
Potential Overfitting: LSTM networks are prone to overfitting, especially when trained on small datasets or when the model capacity is excessively large relative to the available data.

Regularization techniques such as dropout and weight decay are often necessary to prevent overfitting and improve generalization performance.
Difficulty in Interpretability: The internal workings of LSTM networks can be challenging to interpret and understand, especially for non-experts.

The presence of multiple gates, cell states, and hidden states makes it difficult to intuitively grasp how information flows through the network and influences its predictions.
Training Instability: Training LSTM networks may sometimes suffer from instability issues, such as exploding gradients or vanishing gradients, especially in deep architectures or when using suboptimal optimization algorithms.

Careful initialization, gradient clipping, and adaptive learning rate schedules are often required to stabilize the training process.

LSTM FAQ

1) How does LSTM differ from traditional RNNs?

Unlike traditional RNNs, which suffer from the vanishing gradient problem and struggle to capture long-term dependencies, LSTM networks incorporate specialized gating mechanisms to selectively retain and forget information over time, enabling them to effectively capture long-range dependencies.

2) What are the components of an LSTM cell?

An LSTM cell consists of three main gates: the input gate, forget gate, and output gate. These gates regulate the flow of information and gradients within the cell, allowing it to retain or discard information from previous time steps.

4) What is the role of the forget gate in LSTM?

The forget gate determines which information from the previous cell state should be retained and which should be forgotten.

It takes as input the previous cell state and the current input, applies a sigmoid activation function, and outputs a forget vector that scales the previous cell state.

5) How does LSTM handle the vanishing gradient problem?

LSTM networks mitigate the vanishing gradient problem by introducing the forget gate, which allows the network to selectively retain or discard information over time.

This gating mechanism helps prevent gradients from vanishing or exploding during backpropagation, enabling more stable and effective training.

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Attend our Free Webinar on How to Nail Your Next Technical Interview

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Tools to Enhance Full Stack Development with AI

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The Business Impact of Machine Learning: Real-world Case Studies

What is OpenAI? Everything You Need to Know

Mock Interviews for Generative AI: Essential Practice to Land Top AI Roles

Top Python Scripting Interview Questions and Answers You Should Practice

Complex SQL Interview Questions for Interview Preparation

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