From c11d7885e132ba824eec73b191fc638a0b5d978d Mon Sep 17 00:00:00 2001
From: dellaert <dellaert@cc.gatech.edu>
Date: Mon, 13 Oct 2014 11:55:16 +0200
Subject: [PATCH] Comments

---
 gtsam_unstable/nonlinear/Expression-inl.h | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/gtsam_unstable/nonlinear/Expression-inl.h b/gtsam_unstable/nonlinear/Expression-inl.h
index 0bc552985..6f78832b9 100644
--- a/gtsam_unstable/nonlinear/Expression-inl.h
+++ b/gtsam_unstable/nonlinear/Expression-inl.h
@@ -552,10 +552,16 @@ struct GenerateFunctionalNode: Argument<T, A, Base::N + 1>, Base {
 
   /// Construct an execution trace for reverse AD
   void trace(const Values& values, Record* record, char*& raw) const {
-    Base::trace(values, record, raw);
+    Base::trace(values, record, raw); // recurse
+    // Write an Expression<A> execution trace in record->trace
+    // Iff Constant or Leaf, this will not write to raw, only to trace.
+    // Iff the expression is functional, write all Records in raw buffer
+    // Return value of type T is recorded in record->value
     record->Record::This::value = This::expression->traceExecution(values,
         record->Record::This::trace, raw);
-    raw = raw + This::expression->traceSize();
+    // raw is never modified by traceExecution, but if traceExecution has
+    // written in the buffer, the next caller expects we advance the pointer
+    raw += This::expression->traceSize();
   }
 };
 
@@ -590,12 +596,6 @@ struct FunctionalNode {
         return static_cast<JacobianTrace<T, A, N> const &>(*this).value;
       }
 
-      /// Access Trace
-      template<class A, size_t N>
-      ExecutionTrace<A>& trace() {
-        return static_cast<JacobianTrace<T, A, N>&>(*this).trace;
-      }
-
       /// Access Jacobian
       template<class A, size_t N>
       typename Jacobian<T, A>::type& jacobian() {