Abstract: This specification describes machine-learning systems and methods for modelling physical and/or biological systems that apply the principle of maximum entropy to restricted Boltzmann machines. According to a first aspect of this specification, there is described a method for modelling a complex system using machine learning. The method includes: obtaining training data representing the complex system; determining one or more parameters of a parametrised physical model representing the complex system using the training data; and predicting one or more properties of the complex system and/or behaviour of the complex system from the parametrised physical model.