various work on the Sparse module:

* added some glue to Eigen/Core (SparseBit, ei_eval, Matrix)
* add two new sparse matrix types:
   HashMatrix: based on std::map (for random writes)
   LinkedVectorMatrix: array of linked vectors
   (for outer coherent writes, e.g. to transpose a matrix)
* add a SparseSetter class to easily set/update any kind of matrices, e.g.:
   { SparseSetter<MatrixType,RandomAccessPattern> wrapper(mymatrix);
     for (...) wrapper->coeffRef(rand(),rand()) = rand(); }
* automatic shallow copy for RValue
* and a lot of mess !
plus:
* remove the remaining ArrayBit related stuff
* don't use alloca in product for very large memory allocation

Eigen/src/Core/util/Constants.h

@@ -138,10 +138,8 @@ const unsigned int LowerTriangularBit = 0x400;
 
 /** \ingroup flags
   *
-  * means the object is just an array of scalars, and operations on it are regarded as operations
-  * on every of these scalars taken separately.
-  */
-const unsigned int ArrayBit = 0x800;
+  * means the expression includes sparse matrices and the sparse path has to be taken. */
+const unsigned int SparseBit = 0x800;
 
 /** \ingroup flags
   *
@@ -155,7 +153,7 @@ const unsigned int HereditaryBits = RowMajorBit
                                   | EvalBeforeNestingBit
                                   | EvalBeforeAssigningBit
                                   | LargeBit
-                                  | ArrayBit;
+                                  | SparseBit;
 
 // Possible values for the Mode parameter of part() and of extract()
 const unsigned int Upper = UpperTriangularBit;
@@ -173,7 +171,7 @@ enum { Aligned=0, UnAligned=1 };
 enum { ConditionalJumpCost = 5 };
 enum CornerType { TopLeft, TopRight, BottomLeft, BottomRight };
 enum DirectionType { Vertical, Horizontal };
-enum ProductEvaluationMode { NormalProduct, CacheFriendlyProduct, DiagonalProduct };
+enum ProductEvaluationMode { NormalProduct, CacheFriendlyProduct, DiagonalProduct, SparseProduct };
 
 enum {
   InnerVectorization,
@@ -188,5 +186,14 @@ enum {
   NoUnrolling
 };
 
+enum {
+  Dense   = 0,
+  Sparse  = SparseBit
+};
+
+const int FullyCoherentAccessPattern  = 0x1;
+const int InnerCoherentAccessPattern  = 0x2 | FullyCoherentAccessPattern;
+const int OuterCoherentAccessPattern  = 0x4 | InnerCoherentAccessPattern;
+const int RandomAccessPattern         = 0x8 | OuterCoherentAccessPattern;
 
 #endif // EIGEN_CONSTANTS_H

Eigen/src/Core/util/Meta.h

@@ -175,7 +175,9 @@ template<int _Rows, int _Cols> struct ei_size_at_compile_time
   enum { ret = (_Rows==Dynamic || _Cols==Dynamic) ? Dynamic : _Rows * _Cols };
 };
 
-template<typename T> class ei_eval
+template<typename T, int Sparseness = ei_traits<T>::Flags&SparseBit> class ei_eval;
+
+template<typename T> class ei_eval<T,Dense>
 {
     typedef typename ei_traits<T>::Scalar _Scalar;
     enum {_Rows = ei_traits<T>::RowsAtCompileTime,