Space Filling Curve sparse matrix reordering implementations

This is a collection of codes for Space Filling Curve renumbering of sparse matrices. Main code of SFC-renumbering is based on a work by Rakowsky and Fuchs (2011) (http://hdl.handle.net/10013/epic.39576.d001). There is a C++-interface to R, and a demontrator of improved cache-efficiency for Matrix Vector product (SparseM, CSR-fornmat) with a pseudo FE-matrix created on the fly from a FE-like 2D-mesh. We include an R-script applying SFC on the matrix structure, depicted in a 2D-graph representation, rather than on a FE-like mesh. This is achieved by a very fast graph-layout in 2D by pivotMDS on the matrix adjacency structure