diff --git a/gtsam/linear/Preconditioner.h b/gtsam/linear/Preconditioner.h
index 623b29863..31901db3f 100644
--- a/gtsam/linear/Preconditioner.h
+++ b/gtsam/linear/Preconditioner.h
@@ -70,21 +70,20 @@ public:
   Preconditioner() {}
   virtual ~Preconditioner() {}
 
-  /* Computation Interfaces */
+  /* 
+  * Abstract interface for raw vectors. VectorValues is a speed bottleneck
+  * and Yong-Dian has profiled preconditioners (outside GTSAM) with the the
+  * three methods below. In GTSAM, unfortunately, we are still using the
+  * VectorValues methods called in iterative-inl.h
+  */
 
-  /* implement x = L^{-1} y */
+  /// implement x = L^{-1} y
   virtual void solve(const Vector& y, Vector &x) const = 0;
-//  virtual void solve(const VectorValues& y, VectorValues &x) const = 0;
 
-  /* implement x = L^{-T} y */
+  /// implement x = L^{-T} y
   virtual void transposeSolve(const Vector& y, Vector& x) const = 0;
-//  virtual void transposeSolve(const VectorValues& y, VectorValues &x) const = 0;
 
-//  /* implement x = L^{-1} L^{-T} y */
-//  virtual void fullSolve(const Vector& y, Vector &x) const = 0;
-//  virtual void fullSolve(const VectorValues& y, VectorValues &x) const = 0;
-
-  /* build/factorize the preconditioner */
+  /// build/factorize the preconditioner
   virtual void build(
     const GaussianFactorGraph &gfg,
     const KeyInfo &info,
@@ -113,14 +112,7 @@ public:
 
   /* Computation Interfaces for raw vector */
   virtual void solve(const Vector& y, Vector &x) const { x = y; }
-//  virtual void solve(const VectorValues& y, VectorValues& x) const { x = y; }
-
   virtual void transposeSolve(const Vector& y, Vector& x) const { x = y; }
-//  virtual void transposeSolve(const VectorValues& y, VectorValues& x) const { x = y; }
-
-//  virtual void fullSolve(const Vector& y, Vector &x) const { x = y; }
-//  virtual void fullSolve(const VectorValues& y, VectorValues& x) const { x = y; }
-
   virtual void build(
     const GaussianFactorGraph &gfg,
     const KeyInfo &info,
@@ -145,8 +137,6 @@ public:
   /* Computation Interfaces for raw vector */
   virtual void solve(const Vector& y, Vector &x) const;
   virtual void transposeSolve(const Vector& y, Vector& x) const ;
-//  virtual void fullSolve(const Vector& y, Vector &x) const ;
-
   virtual void build(
     const GaussianFactorGraph &gfg,
     const KeyInfo &info,
diff --git a/gtsam/linear/SubgraphPreconditioner.h b/gtsam/linear/SubgraphPreconditioner.h
index e440f32e4..7995afedc 100644
--- a/gtsam/linear/SubgraphPreconditioner.h
+++ b/gtsam/linear/SubgraphPreconditioner.h
@@ -285,15 +285,18 @@ namespace gtsam {
     /*****************************************************************************/
     /* implement virtual functions of Preconditioner */
 
-    /* Computation Interfaces for Vector */
-    virtual void solve(const Vector& y, Vector &x) const;
-    virtual void transposeSolve(const Vector& y, Vector& x) const ;
+    /// implement x = R^{-1} y
+    void solve(const Vector& y, Vector &x) const override;
 
-    virtual void build(
+    /// implement x = R^{-T} y
+    void transposeSolve(const Vector& y, Vector& x) const override;
+
+    /// build/factorize the preconditioner
+    void build(
       const GaussianFactorGraph &gfg,
       const KeyInfo &info,
       const std::map<Key,Vector> &lambda
-      ) ;
+      ) override;
     /*****************************************************************************/
   };
 
@@ -310,9 +313,9 @@ namespace gtsam {
 
 
   /* sort the container and return permutation index with default comparator */
-   template <typename Container>
-   std::vector<size_t> sort_idx(const Container &src)
-   {
+  template <typename Container>
+  std::vector<size_t> sort_idx(const Container &src)
+  {
      typedef typename Container::value_type T;
      const size_t n = src.size() ;
      std::vector<std::pair<size_t,T> > tmp;
@@ -329,6 +332,6 @@ namespace gtsam {
        idx.push_back(tmp[i].first) ;
      }
      return idx;
-   }
+  }
 
 } // namespace gtsam