** Boltzmann machines** (BMs) refer to a synthetic recurrent neural network, often relying on probabilistic graphical models for signification. In short, this particular neural network is well-known for its ability to induce relaxation and consists of both visible and hidden units that are fully interconnected. It employ a stochastic method to learn and portray intricate data patterns, acting as probabilistic generative models.

These machines are also called probability distributions on high-dimensional binary vectors. With hidden nodes, it can represent any arbitrary probability distribution over binary vectors

### What is Deep Learning?

“Deep learning is undeniably mind-blowing” machine learning technique that teaches computers to do what comes naturally to humans: learn by example. It can be used with ease to predict the unpredictable”. Researchers and engineers are busy in creating artificial intelligence by using a combination of non-bio-neural networks and natural intelligence”.

Deep Learning, in short, is going much beyond machine learning and its algorithms that are either supervised or unsupervised. In DL it uses many layers of nonlinear processing units for feature extraction and transformation. It has revolutionized today’s industries by demonstrating near-human-level accuracy in certain tasks. The task like pattern recognition, image classification, voice/text decoding, and many more.

Deep Leaning is a key technology

- To voice control in mobile devices like handphones, TVs, vice command enabled speakers and TVs
- Behind driverless cars, enabling them to recognize a stop sign or to distinguish a pedestrian from a lamppost.
- Has revolutionized, image processing & classification and also speech recognition with high accuracy.

Deep learning is getting lots of attention lately and for good reason. It’s achieving results that were not possible before. Business leaders and developers community absolutely need to understand what it is, what it can do and how it works.

**Boltzmann Machines – Outlook**

Similar to other neural networks, both BMs and RBMs devices comprises an input layer known as the visible layer and one or more hidden layers referred to as the hidden layer. Below are some high-level bullet points for Boltzmann Machines.

– BMs are a type of model that uses energy functions as a means of illustrating the probability distribution of information.*Energy-Based Models*- The energy function distinguishes between likely and unlikely data instances by giving lower energy to the former and higher energy to the latter.
- The goal is to acquire an understanding of the energy function that can detect the core patterns and connections inherent in the data.

– BMs consist of synapses that connect neurons to one another.*Nodes and Connections*- Nodes can either be binary entities, where they take on a value of either 0 or 1, or they can be entities that have continuous values, where they can assume a range of real values.
- The arrangement of nodes in the network involves grouping them into one or more layers, and each node enjoys connections to all other nodes, culminating in a fully integrated and interconnected framework.

– There are two distinct classifications in BMs: Visible units and hidden units.*Visible and Hidden Units*- The visible units represent the input data or observed variables.
- The hidden elements gather the fundamental factors that capture the complex patterns and relationships present in the data.
- The concealed units aid in reconstructing the input data by enabling the model to attain more advanced portrayals.

- Energy Function: To make use of an energy function to assess how suitable the combinations of visible and hidden units are.
- The determination of the energy for a particular configuration depends on the allocation of biases and weights to the connections.
- The energy function is defined by adding the weighted inputs to each unit with their corresponding biases and taking the negative summation.
- Lower energy values suggest a greater probability of configurations.

– BMs use an energy function for creating a probability distribution that covers both the visible and hidden units.*Probability Distribution*- The probability of a specific arrangement is associated with its adverse energy and can be mathematically represented as an exponential equation.
- The normalization constant, also known as the partition function, ensures that the total probability of all possible configurations equals one.

– Acquiring information pertaining to the variables of the energy function, including weights and biases, is imperative when it comes to training Boltzmann machines.*Training*- The process of learning aims to adjust the parameters in a way that enhances the likelihood of the training data.
- Performing accurate inference and parameter adjustments is a difficult undertaking due to the complex interdependencies within the model.
- Boltzmann machines utilize the training algorithms Contrastive Divergence and Persistent Contrastive Divergence, which often incorporate Markov Chain Monte Carlo strategies.

– BMs have demonstrated their usefulness in several applications, such as reducing dimensionality, acquiring features, and producing models.*Applications*- In order to enhance the efficiency of training and constructing representations, restricted Boltzmann machines (RBMs) and deep belief networks (DBNs) have been employed.
- RBMs, which share similarities with Boltzmann machines, have a limited network structure that enhances the learning process.

Boltzmann machines have played a significant role in the advancement of deep learning models and have been instrumental in the comprehension of probabilistic modeling and self-directed learning.

### Boltzmann Machines -A Probabilistic Graphical Models

Boltzmann Machines – A kind of imaginary recurrent neural network and this normally gets interpreted from the probabilistic graphical models. Shortly and concisely, a neural network is fully connected and consists of visible and hidden units. It operates in asynchronous mode with stochastic updates for each of its units.

Sir Geoffrey Hinton, the “Godfather of Deep Learning” coined *Boltzmann *Machine in 1985 for the first time. A well-known figure and personality in the deep learning community Sir Geoffrey Hinton also a professor at the University of Toronto.

It works by updating each of its units in a stochastic manner without requiring synchronization, thus preventing the occurrence of local minima. Simulated annealing is used along with stochastic nodes to further enhance this process.

These machines are also called probability distributions on high-dimensional binary vectors. It’s a generative unsupervised model used for probability distribution from an original dataset. A great, demanding, or hungry tool for computation power, however, by restricting its network topology, the behavior can be controlled.

It is indeed an algorithm that is useful for dimensionality reduction, classification, regression, collaborative filtering, feature learning, and topic modeling.

## Restricted Boltzmann Machines

Boltzmann machines are probability distributions on high dimensional binary vectors which are analogous to Gaussian Markov Random Fields in that they are fully determined by first and second-order moments.

It is used for pattern storage and retrieval. As per Wiki* “A Boltzmann machine is also called stochastic Hopfield network with hidden units) is a type of stochastic recurrent neural network and Markov random field.” *RBM itself has many applications, some of which are listed below

- Collaborative filtering
- Multiclass classification
- Information retrieval
- Motion capture modelling
- Segmentation
- Modelling natural images

Deep belief nets use the Boltzmann machine especially the Restricted Boltzmann machine as a key component but first order weight updates.

In short and in simple words we can say this – The Boltzmann machine, a type of stochastic spin-glass model with an external field, has been subject to various nomenclatures including the Sherrington-Kirkpatrick model with an external field and the Ising-Lenz-Little model. The present work provides a demonstration of a deviation from the conventional Sherrington-Kirkpatrick model, which pertains to the realm of stochastic Ising models.

**Books + Other readings Referred**

- Open Internet
- Hands-on personal research work @
*AILabPage*

**Points to Note:**

All credits, if any, remain with the original contributor. We have now elaborated on BMs in little detail in our post. You can find earlier posts on Machine Learning: The Helicopter View, Supervised Machine Learning, Unsupervised Machine Learning, and Reinforcement Learning here.

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**Conclusion** – While BMs were useful in the past, certain deep learning architectures, such as convolutional neural networks (CNNs) and recurrent neural networks (RNNs), have taken precedence over others because of their effectiveness in various applications, as opposed to the computationally intensive training required for the former. Deep learning, in short, is going much beyond machine learning and its algorithms that are either supervised or unsupervised. In DL, it uses many layers of nonlinear processing units for feature extraction and transformation. In the RBM, hidden units are connected only indirectly through visible units.

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