A geometric view on learning Bayesian network structures

Milan Studený, Jiří Vomlel, Raymond Hemmecke

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

We recall the basic idea of an algebraic approach to learning Bayesian network (BN) structures, namely to represent every BN structure by a certain (uniquely determined) vector, called a standard imset. The main result of the paper is that the set of standard imsets is the set of vertices (=extreme points) of a certain polytope. Motivated by the geometric view, we introduce the concept of the geometric neighborhood for standard imsets, and, consequently, for BN structures. Then we show that it always includes the inclusion neighborhood, which was introduced earlier in connection with the greedy equivalence search (GES) algorithm. The third result is that the global optimum of an affine function over the polytope coincides with the local optimum relative to the geometric neighborhood. To illustrate the new concept by an example, we describe the geometric neighborhood in the case of three variables and show it differs from the inclusion neighborhood. This leads to a simple example of the failure of the GES algorithm if data are not " generated" from a perfectly Markovian distribution. The point is that one can avoid this failure if the search technique is based on the geometric neighborhood instead. We also found out what is the geometric neighborhood in the case of four and five variables.

Original languageEnglish
Pages (from-to)573-586
Number of pages14
JournalInternational Journal of Approximate Reasoning
Volume51
Issue number5
DOIs
StatePublished - Jun 2010

Keywords

  • GES algorithm
  • Geometric neighborhood
  • Inclusion neighborhood
  • Learning Bayesian networks
  • Standard imset

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