Authors
Pirapong Singsathid
Deparment of Mathematics, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand
Pikul Puphasuk
Deparment of Mathematics, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand
Jeerayut Wetweerapong
Deparment of Mathematics, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand