improve DiscreteConditional::argmax method to accept parent values

gtsam/discrete/DiscreteConditional.cpp

@@ -235,16 +235,16 @@ DecisionTreeFactor::shared_ptr DiscreteConditional::likelihood(
 }
 
 /* ************************************************************************** */
-size_t DiscreteConditional::argmax() const {
+size_t DiscreteConditional::argmax(const DiscreteValues& parentsValues) const {
   size_t maxValue = 0;
   double maxP = 0;
+  DiscreteValues values = parentsValues;
+
   assert(nrFrontals() == 1);
-  assert(nrParents() == 0);
-  DiscreteValues frontals;
   Key j = firstFrontalKey();
   for (size_t value = 0; value < cardinality(j); value++) {
-    frontals[j] = value;
-    double pValueS = (*this)(frontals);
+    values[j] = value;
+    double pValueS = (*this)(values);
     // Update MPE solution if better
     if (pValueS > maxP) {
       maxP = pValueS;

gtsam/discrete/DiscreteConditional.h

@@ -217,7 +217,7 @@ class GTSAM_EXPORT DiscreteConditional
    * @brief Return assignment that maximizes distribution.
    * @return Optimal assignment (1 frontal variable).
    */
-  size_t argmax() const;
+  size_t argmax(const DiscreteValues& parentsValues = DiscreteValues()) const;
 
   /// @}
   /// @name Advanced Interface

gtsam/discrete/tests/testDiscreteConditional.cpp

@@ -289,6 +289,29 @@ TEST(DiscreteConditional, choose) {
   EXPECT(assert_equal(expected3, *actual3, 1e-9));
 }
 
+/* ************************************************************************* */
+// Check argmax on P(C|D) and P(D)
+TEST(DiscreteConditional, Argmax) {
+  DiscreteKey C(2, 2), D(4, 2);
+  DiscreteConditional D_cond(D, "1/3");
+  DiscreteConditional C_given_DE((C | D) = "1/4 1/1");
+
+  // Case 1: No parents
+  size_t actual1 = D_cond.argmax();
+  EXPECT_LONGS_EQUAL(1, actual1);
+
+  // Case 2: Given parent values
+  DiscreteValues given;
+  given[D.first] = 1;
+  size_t actual2 = C_given_DE.argmax(given);
+  // Should be 0 since D=1 gives 0.5/0.5
+  EXPECT_LONGS_EQUAL(0, actual2);
+  
+  given[D.first] = 0;
+  size_t actual3 = C_given_DE.argmax(given);
+  EXPECT_LONGS_EQUAL(1, actual3);
+}
+
 /* ************************************************************************* */
 // Check markdown representation looks as expected, no parents.
 TEST(DiscreteConditional, markdown_prior) {