* added innerSize / outerSize functions to MatrixBase

* added complete implementation of sparse matrix product
  (with a little glue in Eigen/Core)
* added an exhaustive bench of sparse products including GMM++ and MTL4
  => Eigen outperforms in all transposed/density configurations !

bench/BenchSparseUtil.h

@@ -0,0 +1,75 @@
+
+#include <Eigen/Array>
+#include <Eigen/Sparse>
+#include <bench/BenchTimer.h>
+
+
+
+using namespace std;
+using namespace Eigen;
+USING_PART_OF_NAMESPACE_EIGEN
+
+#ifndef SIZE
+#define SIZE 1024
+#endif
+
+#ifndef DENSITY
+#define DENSITY 0.01
+#endif
+
+#ifndef SCALAR
+#define SCALAR float
+#endif
+
+typedef SCALAR Scalar;
+typedef Matrix<Scalar,Dynamic,Dynamic> DenseMatrix;
+typedef SparseMatrix<Scalar> EigenSparseMatrix;
+
+void fillMatrix(float density, int rows, int cols,  EigenSparseMatrix& dst)
+{
+  dst.startFill(rows*cols*density);
+  for(int j = 0; j < cols; j++)
+  {
+    for(int i = 0; i < rows; i++)
+    {
+      Scalar v = (ei_random<float>(0,1) < density) ? ei_random<Scalar>() : 0;
+      if (v!=0)
+        dst.fill(i,j) = v;
+    }
+  }
+  dst.endFill();
+}
+
+void eiToDense(const EigenSparseMatrix& src, DenseMatrix& dst)
+{
+  dst.setZero();
+  for (int j=0; j<src.cols(); ++j)
+    for (EigenSparseMatrix::InnerIterator it(src.derived(), j); it; ++it)
+      dst(it.index(),j) = it.value();
+}
+
+#ifndef NOGMM
+#include "gmm/gmm.h"
+typedef gmm::csc_matrix<Scalar> GmmSparse;
+typedef gmm::col_matrix< gmm::wsvector<Scalar> > GmmDynSparse;
+void eiToGmm(const EigenSparseMatrix& src, GmmSparse& dst)
+{
+  GmmDynSparse tmp(src.rows(), src.cols());
+  for (int j=0; j<src.cols(); ++j)
+    for (EigenSparseMatrix::InnerIterator it(src.derived(), j); it; ++it)
+      tmp(it.index(),j) = it.value();
+  gmm::copy(tmp, dst);
+}
+#endif
+
+#ifndef NOMTL
+#include <boost/numeric/mtl/mtl.hpp>
+typedef mtl::compressed2D<Scalar> MtlSparse;
+void eiToMtl(const EigenSparseMatrix& src, MtlSparse& dst)
+{
+  mtl::matrix::inserter<MtlSparse> ins(dst);
+  for (int j=0; j<src.cols(); ++j)
+    for (EigenSparseMatrix::InnerIterator it(src.derived(), j); it; ++it)
+      ins[it.index()][j] = it.value();
+}
+#endif