Author/Authors :
Sadeghi، Gh. نويسنده Department of Mathematics and Computer Sciences, Hakim Sabzevari University, Sabzevar, Iran , , Azadifar، B. نويسنده Department of Mathematics and Computer Sciences, Hakim Sabzevari University, Sabzevar, Iran , , Maramaei، M. نويسنده Department of Mathematics and Computer Sciences, Hakim Sabzevari University, Sabzevar, Iran ,