Volume 12, Issue 1, November 2014, Pages 328–335




Hendra Cipta1, Siti Aisyah2, and Maimunah Rahmadani3
1 Graduate School of Mathematics, University of Sumatera Utara, Campus USU Medan, 20155, Indonesia
2 Graduate School of Mathematics, University of Sumatera Utara, Campus USU Medan, 20155, Indonesia
3 Graduate School of Mathematics, University of Sumatera Utara, Campus USU Medan, 20155, Indonesia