[Probability] Polytree


  • (1) singly connected, (2) no loops, (3) at most one path between any two nodes
  • Efficient algorithms for exact inference


Screen Shot 2018-10-29 at 1.29.49 AMScreen Shot 2018-10-29 at 1.29.56 AMScreen Shot 2018-10-29 at 1.30.09 AMScreen Shot 2018-10-29 at 1.30.17 AM


  • Termination
    • Root node does not have parents, so probability will be given.
    • Leaf node does not have children, so no recursive call can happen down stream.
    • Computing Evidence node’s probability is trivial, because it can be done by recursive call of marginalization. (Trivial)
  • Runtime analysis
    • Linear in number of nodes and in size of CPTs.
  • Problem solving in general
    • Start off with Bayes rule if the order is wierd, Product rule to remove something, Marginalization if something is missing…



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