1. ME S.r.l., via Giambellino 7, 35129, Padova, Italy, and Department ICEA, University of Padova, via Marzolo 9, 35131, Padova, Italy.
2. Corresponding author. Department ICEA, University of Padova, via Marzolo 9, 35131, Padova, Italy.
3. Department of Mathematics and Statistics, University of New Mexico, Albuquerque, NM 87131 USA.
4. Siebel Center for Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801 USA.