1. Université Clermont Auvergne, Clermont Auvergne INP, CNRS, Institut Pascal, F-63000 Clermont-Ferrand, France.
2. INSA Rouen Normandie, Normandie Univ, LMI UR 3226, F-76000 Rouen, France.
3. Department of Mathematics, University of California at Los Angeles, Los Angeles, CA 90095 USA.