2. Recurrent Neural Networks (RNNs)

Recurrent Neural Networks (RNNs) are a type of artificial neural network architecture that is specifically designed to process sequential data, where the order of the data points matters. Unlike feed-forward neural networks (FNNs) that process data in a single pass from the input layer to the output layer, RNNs have recurrent connections that allow them to maintain an internal memory or state, enabling them to capture and process sequential information.

In an RNN, the output of a previous step is fed back into the network as input for the current step, creating a loop-like structure. This allows the network to take into account not only the current input but also the information it has seen in previous steps or time points. The internal state of an RNN serves as a form of memory that helps the network retain and utilize information from the past when making predictions or decisions.

RNNs have a hidden state that is updated at each time step based on the current input and the previous hidden state. This hidden state serves as the memory of the network and captures the contextual information from the past. The output at each time step can be derived from the hidden state or passed through additional layers before producing the final output.

RNNs are well-suited for processing and modeling sequential data, such as time series, speech, natural language, and music. They can handle variable-length inputs and capture dependencies over time. However, traditional RNNs suffer from the "vanishing gradient" problem, where the gradients used for learning tend to diminish or explode exponentially over time, making it difficult to capture long-term dependencies.

To address the vanishing gradient problem, various advanced RNN architectures have been developed, including Long Short-Term Memory (LSTM) networks and Gated Recurrent Units (GRUs). LSTM and GRU networks incorporate specialized memory cells and gating mechanisms that allow them to selectively retain and update information, making them more effective at capturing long-term dependencies in sequential data.

In summary, RNNs are a type of neural network architecture that can handle sequential data by maintaining an internal memory or state. They are distinct from feed-forward neural networks (FNNs), which process data in a single pass and do not have recurrent connections. While RNNs are a powerful tool for modeling sequential data, more advanced variants such as LSTM and GRU networks are commonly used to overcome the vanishing gradient problem and capture long-term dependencies.

Types of Recurrent Neural Network architectures;

(a) Basic Recurrent Neural Networks

(b) Long Short-Term Memory Networks (LSTMs)

(c) Gated Recurrent Units (GRUs)

(d) Bidirectional RNNs

(e) Sequence to Sequence models (often used for tasks like translation)