# What is the application for using the Boltzmann Machines?

I've came across this post from wikipedia about Boltzmann machines, which concludes that it is not a model that is usually used in practice, and that its' constrained version (i.e. where the network resembles a bipartite graph) is more usable.

My question is - what the Boltzmann machines are used for, and why is the constrained version is more usable than the unconstrained one?

The idea behind the Boltzmann Machine is that it represents a closed system where an energy flows from one part to another, i.e. heat dissipation, and models the decrease in the entropy of a closed model - while the model starts with relatively low entropy (i.e. when there is a separation between 'hot' and 'cold' parts), it tends to the state of equilibrium, or high entropy (i.e. all the items of the same energy, or 'heat'). Those networks are a type of Hopfield networks, which are used for associative memory modelling (here is the link from wikipedia).
2. The answer for the first question is also in part an answer for the second, but in addition to it, Constrained Boltzmann Networks may model a more realistic scenarios, where nodes are divided into two separate groups, and the edges between them may represent weight of data flow, etc.