1. Institute of Production and Supply Chain Management, Technische Universität Darmstadt, Darmstadt, Germany;
2. Department of Mathematics and Statistics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, Thailand;
3. Applied Analysis Research Unit, Department of Mathematics and Statistics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, Thailand;
4. Centre of Excellence in Mathematics, Commission of Higher Education, Bangkok, Thailand