New discrete example

examples/DiscreteBayesNetExample.cpp

@@ -0,0 +1,82 @@
+/* ----------------------------------------------------------------------------
+
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
+ * Atlanta, Georgia 30332-0415
+ * All Rights Reserved
+ * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
+
+ * See LICENSE for the license information
+
+ * -------------------------------------------------------------------------- */
+
+/**
+ * @file  DiscreteBayesNetExample.cpp
+ * @brief   Discrete Bayes Net example with famous Asia Bayes Network
+ * @author  Frank Dellaert
+ * @date  JULY 10, 2020
+ */
+
+#include <gtsam/discrete/DiscreteFactorGraph.h>
+#include <gtsam/discrete/DiscreteMarginals.h>
+
+#include <iomanip>
+
+using namespace std;
+using namespace gtsam;
+
+int main(int argc, char **argv) {
+  DiscreteBayesNet asia;
+  DiscreteKey Asia(0, 2), Smoking(4, 2), Tuberculosis(3, 2), LungCancer(6, 2),
+      Bronchitis(7, 2), Either(5, 2), XRay(2, 2), Dyspnea(1, 2);
+  asia.add(Asia % "99/1");
+  asia.add(Smoking % "50/50");
+
+  asia.add(Tuberculosis | Asia = "99/1 95/5");
+  asia.add(LungCancer | Smoking = "99/1 90/10");
+  asia.add(Bronchitis | Smoking = "70/30 40/60");
+
+  asia.add((Either | Tuberculosis, LungCancer) = "F T T T");
+
+  asia.add(XRay | Either = "95/5 2/98");
+  asia.add((Dyspnea | Either, Bronchitis) = "9/1 2/8 3/7 1/9");
+
+  // print
+  vector<string> pretty = {"Asia",    "Dyspnea", "XRay",       "Tuberculosis",
+                           "Smoking", "Either",  "LungCancer", "Bronchitis"};
+  auto formatter = [pretty](Key key) { return pretty[key]; };
+  asia.print("Asia", formatter);
+
+  // Convert to factor graph
+  DiscreteFactorGraph fg(asia);
+
+  // Create solver and eliminate
+  Ordering ordering;
+  ordering += Key(0), Key(1), Key(2), Key(3), Key(4), Key(5), Key(6), Key(7);
+  DiscreteBayesNet::shared_ptr chordal = fg.eliminateSequential(ordering);
+
+  // solve
+  DiscreteFactor::sharedValues mpe = chordal->optimize();
+  GTSAM_PRINT(*mpe);
+
+  // We can also build a Bayes tree (directed junction tree).
+  // The elimination order above will do fine:
+  auto bayesTree = fg.eliminateMultifrontal(ordering);
+  bayesTree->print("bayesTree", formatter);
+
+  // add evidence, we were in Asia and we have dyspnea
+  fg.add(Asia, "0 1");
+  fg.add(Dyspnea, "0 1");
+
+  // solve again, now with evidence
+  DiscreteBayesNet::shared_ptr chordal2 = fg.eliminateSequential(ordering);
+  DiscreteFactor::sharedValues mpe2 = chordal2->optimize();
+  GTSAM_PRINT(*mpe2);
+
+  // We can also sample from it
+  cout << "\n10 samples:" << endl;
+  for (size_t i = 0; i < 10; i++) {
+    DiscreteFactor::sharedValues sample = chordal2->sample();
+    GTSAM_PRINT(*sample);
+  }
+  return 0;
+}

examples/DiscreteBayesNet_FG.cpp

@@ -10,7 +10,7 @@
  * -------------------------------------------------------------------------- */
 
 /**
- * @file  DiscreteBayesNet_graph.cpp
+ * @file  DiscreteBayesNet_FG.cpp
  * @brief   Discrete Bayes Net example using Factor Graphs
  * @author  Abhijit
  * @date  Jun 4, 2012