Examples of GibbsAsk

aima.core.probability.bayes.approx.GibbsAsk

Artificial Intelligence A Modern Approach (3rd Edition): page 537.

 function GIBBS-ASK(X, e, bn, N) returns an estimate of P(X|e) local variables: N, a vector of counts for each value of X, initially zero Z, the nonevidence variables in bn x, the current state of the network, initially copied from e initialize x with random values for the variables in Z for j = 1 to N do for each Z_i in Z do set the value of Z_i in x by sampling from P(Z_i|mb(Z_i)) N[x] <- N[x] + 1 where x is the value of X in x return NORMALIZE(N)

Figure 14.16 The Gibbs sampling algorithm for approximate inference in Bayesian networks; this version cycles through the variables, but choosing variables at random also works.

Note: The implementation has been extended to handle queries with multiple variables.
@author Ciaran O'Reilly @author Ravi Mohan

  public static void bayesGibbsAskDemo() {
    System.out.println("DEMO: Bayes Gibbs Ask N = " + NUM_SAMPLES);
    System.out.println("=====================");
    demoToothacheCavityCatchModel(new FiniteBayesModel(
        BayesNetExampleFactory.constructToothacheCavityCatchNetwork(),
        new BayesInferenceApproxAdapter(new GibbsAsk(), NUM_SAMPLES)));
    demoBurglaryAlarmModel(new FiniteBayesModel(
        BayesNetExampleFactory.constructBurglaryAlarmNetwork(),
        new BayesInferenceApproxAdapter(new GibbsAsk(), NUM_SAMPLES)));
    System.out.println("=====================");
  }

    AssignmentProposition[] e = new AssignmentProposition[] { new AssignmentProposition(
        ExampleRV.SPRINKLER_RV, Boolean.TRUE) };
    MockRandomizer r = new MockRandomizer(new double[] { 0.5, 0.5, 0.5,
        0.5, 0.5, 0.5, 0.6, 0.5, 0.5, 0.6, 0.5, 0.5 });


    GibbsAsk ga = new GibbsAsk(r);


    double[] estimate = ga.gibbsAsk(
        new RandomVariable[] { ExampleRV.RAIN_RV }, e, bn, 3)
        .getValues();


    Assert.assertArrayEquals(new double[] { 0.3333333333333333,
        0.6666666666666666 }, estimate, DELTA_THRESHOLD);

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Examples of GibbsAsk

Examples of aima.core.probability.bayes.approx.GibbsAsk

Examples of aima.core.probability.bayes.approx.GibbsAsk