Graphical models are widely used to encode conditional independence constraints and causal assumptions, the directed acyclic graph (DAG) being one of the most common families of models. However, DAGs are not closed under marginalization: that is, if a distribution is Markov with respect to a DAG, several of its marginals might not be representable with another DAG unless one discards some of the structural independencies. Acyclic directed mixed graphs (ADMGs) generalize DAGs so that closure under marginalization is possible. In a previous work, we showed how to perform Bayesian inference to infer the posterior distribution of the parameters of a given Gaussian ADMG model, where the graph is fixed. In this paper, we extend this procedure to allow for priors over graph structures.Key words: Graphical models, Bayesian inference, sparsity.
Acyclic Directed Mixed Graph ModelsDirected acyclic graphs (DAGs) provide a practical language to encode conditional independence constraints (see, e.g., [8]). However, such a family is not closed under marginalization. As an illustration of this concept, consider the following DAG:This model entails several conditional independencies. For instance, it encodes constraints such as Y 2 ⊥ ⊥ Y 4 , as well asDirected graphical models are non-monotonic independence models, in the sense that conditioning on extra variables can destroy and re-create independencies, as the sequence { / 0, {Y 3 }, {Y 3 , X}} has demonstrated.