1. Department of Mathematics Southwestern University of Finance and Economics Chengdu China
2. Faculty of Mathematics Federal University of Pará Salinópolis Brazil
3. Universidade Estadual do Maranhão Cidade Universitária Paulo VI, Av. Lourenço Vieira da Silva Maranhão, São Luís Brazil
4. Institute of Exact and Natural Sciences Federal University of Pará Belém Brazil