What is a Restricted Boltzmann Machines in AI/ML?

A Restricted Boltzmann Machine (RBM) is a type of artificial neural network used in artificial intelligence (AI) and machine learning (ML). RBMs are a type of generative stochastic artificial neural network that can learn a probability distribution over its set of inputs. They are particularly well-suited for dimensionality reduction, feature learning, and collaborative filtering tasks.

RBMs can be used as building blocks to create more complex neural networks, such as deep belief networks (DBNs). DBNs are stacked RBMs, where the output of one RBM is the input to the next RBM. DBNs have been used to achieve state-of-the-art results on a variety of tasks

Key characteristics and components of Restricted Boltzmann Machines include:

1. Architecture: An RBM consists of two layers of nodes: a visible layer and a hidden layer. Each node in one layer is connected to every node in the other layer, but there are no connections within the same layer. This architecture is "restricted" because of this absence of connections between nodes within a layer.
2. Stochastic Activation: RBMs use stochastic binary activations. Each node in both the visible and hidden layers can take on binary values (0 or 1) with probabilities determined by the node's activation function, which is typically a logistic (sigmoid) function.
3. Energy-Based Model: RBMs are an energy-based model. They assign an energy value to each possible configuration of the visible and hidden layers. Low energy configurations are more probable, while high energy configurations are less probable.
4. Bipartite Graph: The connectivity pattern of RBMs forms a bipartite graph, meaning that no two nodes within the same layer are connected. This architecture allows for efficient training and sampling.
5. Training: RBMs are trained using a contrastive divergence (CD) algorithm or variants like persistent contrastive divergence. Training aims to minimize the difference between the observed data distribution and the distribution modeled by the RBM.