[1] Politecn Milan, Dipartimento Matemat, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy
[2] Tohoku Univ, Grad Sch Informat Sci, Sendai, Miyagi 9808579, Japan
[3] Hankyong Natl Univ, Dept Appl Math, 327 Jungang Ro, Anseong 17579, Gyeonggi Do, South Korea
[4] Hankyong Natl Univ, Inst Integrated Math Sci, 327 Jungang Ro, Anseong 17579, Gyeonggi Do, South Korea