1. MOX-Laboratory for Modeling and Scientific Computing, Department of Mathematics, Politecnico di Milano, P.za Leonardo da Vinci, Milano, Italy
2. CMCS, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
3. MOX-Laboratory for Modeling and Scientific Computing, Department of Mathematics, Politecnico di Milano, Piazza Leonardo da Vinci, Milano, Italy (on leave)