Author/Authors :
Ehsani، A. نويسنده Department of Mathematics, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran Ehsani, A. , Movsisyan، Y. نويسنده Department of Mathematics and Mechanics, Yerevan State University, Alex Manoogian 1, Yerevan 0025, Armenia Movsisyan, Y.