Fix DecisionTreeFactor division

gtsam/discrete/DecisionTreeFactor.h

@@ -18,6 +18,7 @@
 
 #pragma once
 
+#include <gtsam/discrete/Signature.h>
 #include <gtsam/discrete/AlgebraicDecisionTree.h>
 #include <gtsam/discrete/DiscreteFactor.h>
 #include <gtsam/discrete/DiscreteKey.h>
@@ -116,6 +117,10 @@ namespace gtsam {
     DecisionTreeFactor(const DiscreteKey& key, const std::vector<double>& row)
         : DecisionTreeFactor(DiscreteKeys{key}, row) {}
 
+    /// Construct from Signature
+    DecisionTreeFactor(const Signature& signature)
+        : DecisionTreeFactor(signature.discreteKeys(), signature.cpt()) {}
+
     /** Construct from a DiscreteConditional type */
     explicit DecisionTreeFactor(const DiscreteConditional& c);
 
@@ -156,7 +161,15 @@ namespace gtsam {
 
     /// divide by factor f (safely)
     DecisionTreeFactor operator/(const DecisionTreeFactor& f) const {
-      return apply(f, safe_div);
+      KeyVector diff;
+      std::set_difference(this->keys().begin(), this->keys().end(),
+                          f.keys().begin(), f.keys().end(),
+                          std::back_inserter(diff));
+      DiscreteKeys keys;
+      for (Key key : diff) {
+        keys.push_back({key, this->cardinality(key)});
+      }
+      return DecisionTreeFactor(keys, apply(f, safe_div));
     }
 
     /// Convert into a decision tree

gtsam/discrete/tests/testDecisionTreeFactor.cpp

@@ -69,6 +69,15 @@ TEST(DecisionTreeFactor, constructors) {
   EXPECT_DOUBLES_EQUAL(0.8, f4(x121), 1e-9);
 }
 
+/* ************************************************************************* */
+TEST(DecisionTreeFactor, Divide) {
+  DiscreteKey A(0, 2), S(1, 2);
+  DecisionTreeFactor pA(A % "99/1"), pS(S % "50/50");
+  DecisionTreeFactor joint = pA * pS;
+  DecisionTreeFactor s = joint / pA;
+  EXPECT(assert_equal(pS, s));
+}
+
 /* ************************************************************************* */
 TEST(DecisionTreeFactor, Error) {
   // Declare a bunch of keys
@@ -217,27 +226,21 @@ void maybeSaveDotFile(const DecisionTreeFactor& f, const string& filename) {
 #endif
 }
 
-/** Convert Signature into CPT */
-DecisionTreeFactor create(const Signature& signature) {
-  DecisionTreeFactor p(signature.discreteKeys(), signature.cpt());
-  return p;
-}
-
 /* ************************************************************************* */
 // test Asia Joint
 TEST(DecisionTreeFactor, joint) {
   DiscreteKey A(0, 2), S(1, 2), T(2, 2), L(3, 2), B(4, 2), E(5, 2), X(6, 2),
       D(7, 2);
 
   gttic_(asiaCPTs);
-  DecisionTreeFactor pA = create(A % "99/1");
-  DecisionTreeFactor pS = create(S % "50/50");
-  DecisionTreeFactor pT = create(T | A = "99/1 95/5");
-  DecisionTreeFactor pL = create(L | S = "99/1 90/10");
-  DecisionTreeFactor pB = create(B | S = "70/30 40/60");
-  DecisionTreeFactor pE = create((E | T, L) = "F T T T");
-  DecisionTreeFactor pX = create(X | E = "95/5 2/98");
-  DecisionTreeFactor pD = create((D | E, B) = "9/1 2/8 3/7 1/9");
+  DecisionTreeFactor pA(A % "99/1");
+  DecisionTreeFactor pS(S % "50/50");
+  DecisionTreeFactor pT(T | A = "99/1 95/5");
+  DecisionTreeFactor pL(L | S = "99/1 90/10");
+  DecisionTreeFactor pB(B | S = "70/30 40/60");
+  DecisionTreeFactor pE((E | T, L) = "F T T T");
+  DecisionTreeFactor pX(X | E = "95/5 2/98");
+  DecisionTreeFactor pD((D | E, B) = "9/1 2/8 3/7 1/9");
 
   // Create joint
   gttic_(asiaJoint);