update comments

gtsam/discrete/DecisionTreeFactor.cpp

@@ -548,6 +548,9 @@ namespace gtsam {
 DiscreteFactor::shared_ptr DecisionTreeFactor::restrict(
     const DiscreteValues& assignment) const {
   ADT restricted_tree = ADT::restrict(assignment);
+  // Get all the keys that are not restricted by the assignment
+  // This ensures that the new restricted factor doesn't have keys
+  // for which the information has been removed.
   DiscreteKeys restricted_keys = this->discreteKeys();
   for (auto&& kv : assignment) {
     Key key = kv.first;
@@ -557,6 +560,7 @@ DiscreteFactor::shared_ptr DecisionTreeFactor::restrict(
                        [key](const DiscreteKey& k) { return k.first == key; }),
         restricted_keys.end());
   }
+  // Create the restricted factor with the appropriate keys and tree.
   return std::make_shared<DecisionTreeFactor>(restricted_keys, restricted_tree);
 }
 

gtsam/hybrid/HybridNonlinearFactorGraph.cpp

@@ -237,8 +237,11 @@ HybridNonlinearFactorGraph HybridNonlinearFactorGraph::restrict(
       result.push_back(hf->restrict(discreteValues));
     } else if (auto df = dynamic_pointer_cast<DiscreteFactor>(f)) {
       auto restricted_df = df->restrict(discreteValues);
-      // In the case where all the discrete values have been selected,
-      // we ignore the factor since it doesn't add any information
+      // In the case where all the discrete values in the factor
+      // have been selected, we get a factor without any keys,
+      // and default values of 0.5.
+      // Since this factor no longer adds any information, we ignore it to make
+      // inference faster.
       if (restricted_df->discreteKeys().size() > 0) {
         result.push_back(restricted_df);
       }