1. Constantin Brancusi University, Republicii 1, Targu-Jiu, Romania
2. Faculty of Basic Education Banking University, Ho Chi Minh city, Vietnam
3. Division of Computational Mathematics and Engineering, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam
4. Faculty of Mathematics and Statistics, Ton Duc Thang University, Ho Chi Minh City, Vietnam