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Vidip Ghosh
Vidip Ghosh

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The Evolution of Sequential Learning Models: RNN LSTM Transformers

Recurrent Neural Networks (RNNs) are used for processing sequential or time-series data by maintaining a hidden states that captures memory of past inputs within a sequence.

They have a feedback loop, meaning each output depends on the previous inputs — making them ideal for tasks like sentiment analysis or speech recognition.

However, RNNs face key challenges:

  • Vanishing gradient problem – they struggle to learn long-term dependencies.
  • Limited memory – as sequences get longer, they gradually forget earlier information.

Long Short-Term Memory (LSTM) networks come into the picture as an improved version of RNNs, designed to solve the problems of vanishing gradients and long-term dependency.

Unlike traditional RNNs, LSTMs have a memory cell that helps retain important information for longer durations — allowing them to "remember" context across longer sequences.

Architecture Overview:

  • Forget Gate: Decides which part of the previous cell state to keep or forget.
  • Input Gate: It is actually the one that adds new information into the memory cell.
  • Output Gate: Controls what information is passed to the next step.

Real use case: Grammar correction tools like QuillBot, which rely on understanding long text dependencies to rephrase sentences accurately.

However LSTM face key challenges:

  • Computationally Expensive
  • Requires more memory.

LSTMs can’t analyze an entire sentence at once since they process information sequentially, step by step.
This is where Transformers come in — self-attention-based models designed for processing natural language efficiently. Unlike RNNs or LSTMs, Transformers process entire sentences in parallel, allowing them to capture context and relationships between words more effectively.
Examples: ChatGPT, BERT, GPT-4

Key Features:

  • Capable of performing Sequence-to-Sequence tasks (e.g., language translation).
  • Built using multiple encoder–decoder layers for deeper understanding.

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