* add a Make* expression type builder to allow the

construction of generic expressions working
  for both dense and sparse matrix. A nicer solution
  would be to use CwiseBinaryOp for any kind of matrix.
  To this end we either need to change the overall design
  so that the base class(es) depends on the kind of matrix,
  or we could add a template parameter to each expression
  type (e.g., int Kind = ei_traits<MatrixType>::Kind)
  allowing to specialize each expression for each kind of matrix.
* Extend AutoDiffScalar to work with sparse vector expression
  for the derivatives.

Eigen/Sparse

@@ -110,6 +110,7 @@ namespace Eigen {
 #include "src/Sparse/SparseLLT.h"
 #include "src/Sparse/SparseLDLT.h"
 #include "src/Sparse/SparseLU.h"
+#include "src/Sparse/SparseExpressionMaker.h"
 
 #ifdef EIGEN_CHOLMOD_SUPPORT
 # include "src/Sparse/CholmodSupport.h"