[1] Lund Univ, Ctr Math Sci, Box 118, S-22100 Lund, Sweden
[2] Tech Univ Denmark, DTU Compute, Build 303B, DK-2800 Lyngby, Denmark
[3] Univ Copenhagen, Dept Math Sci, Univ Pk 5, DK-2100 Copenhagen, Denmark
[4] Roskilde Univ, Dept Sci & Environm, DK-4000 Roskilde, Denmark