From 6c6c545d99f2542864e7fe3ea6bce3319f44905c Mon Sep 17 00:00:00 2001
From: dellaert <dellaert@cc.gatech.edu>
Date: Tue, 6 May 2014 01:33:09 -0400
Subject: [PATCH] Comments

---
 gtsam/linear/GaussianConditional.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/gtsam/linear/GaussianConditional.cpp b/gtsam/linear/GaussianConditional.cpp
index c6bd3967b..a5c651a44 100644
--- a/gtsam/linear/GaussianConditional.cpp
+++ b/gtsam/linear/GaussianConditional.cpp
@@ -119,14 +119,20 @@ namespace gtsam {
   /* ************************************************************************* */
   VectorValues GaussianConditional::solve(const VectorValues& x) const
   {
-    // Solve matrix
+    // Concatenate all vector values that correspond to parent variables
     Vector xS = x.vector(FastVector<Key>(beginParents(), endParents()));
+
+    // Update right-hand-side
     xS = getb() - get_S() * xS;
+
+    // Solve matrix
     Vector soln = get_R().triangularView<Eigen::Upper>().solve(xS);
 
     // Check for indeterminant solution
     if(soln.hasNaN()) throw IndeterminantLinearSystemException(keys().front());
 
+    // TODO, do we not have to scale by sigmas here? Copy/paste bug
+
     // Insert solution into a VectorValues
     VectorValues result;
     DenseIndex vectorPosition = 0;
@@ -142,9 +148,14 @@ namespace gtsam {
   VectorValues GaussianConditional::solveOtherRHS(
     const VectorValues& parents, const VectorValues& rhs) const
   {
+    // Concatenate all vector values that correspond to parent variables
     Vector xS = parents.vector(FastVector<Key>(beginParents(), endParents()));
+
+    // Instead of updating getb(), update the right-hand-side from the given rhs
     const Vector rhsR = rhs.vector(FastVector<Key>(beginFrontals(), endFrontals()));
     xS = rhsR - get_S() * xS;
+
+    // Solve Matrix
     Vector soln = get_R().triangularView<Eigen::Upper>().solve(xS);
 
     // Scale by sigmas