Ashraf, M. M., M. Obaid Ullah, T. N. Malik, A. B. Waqas, M. Iqbal, and F. Siddiq. 2018. “Robust Extraction of Harmonics Using Heuristic Advanced Gravitational Search Algorithm-Based Least Square Estimator”. The Nucleus 54 (4):219-31. http://www.thenucleuspak.org.pk/index.php/Nucleus/article/view/273.