1. Department of Mathematics University of Malakand Chakdara, 18800 Dir (L), Khyber Pakhtunkhwa, Pakistan
2. Department of Mathematics, University of Swat, 01923 Swat, Khyber Pakhtunkhwa, Pakistan
3. Department of Electricity and Electronics, Institute of Research and Development of Processes, University of the Basque Country, Campus of Leioa 48940- Leioa (Bizkaia), Spain