1. Department of Mathematics, Khorramabad Branch, Islamic Azad University, Khorramabad 6817816645, Iran
2. Department of Mathematics, Shiraz Branch, Islamic Azad University, Shiraz 71993-1, Iran
3. COPPEAD Graduate Business School, Federal University of Rio de Janeiro, Rua Paschoal Lemme, 355, Rio de Janeiro 21941-901, Brazil
4. School of Management, University of Bradford, Bradford BD7 1DP, UK