1. Division of Computational Mathematics and Physics, FSCN, Mid Sweden Univ., SE-851 70, Sundsvall, SE (Corresponding author), e-mail: sverker.edvardsson@miun.se
2. Division of Computational Mathematics and Physics, FSCN, Mid Sweden Univ., SE-851 70, Sundsvall, SE, e-mail: per.gradin@miun.se
3. Division of Computational Mathematics and Physics, FSCN, Mid Sweden Univ., SE-851 70, Sundsvall, SE, e-mail: per.isaksson@miun.se
4. Division of Computational Mathematics and Physics, FSCN, Mid Sweden Univ., SE-851 70, Sundsvall, SE, e-mail: marten.gulliksson@miun.se