Abbas Yakubu, Usman, et al. “Secant Condition Free of a Spectral Hestenses-Stiefel (SHS) Conjugate Gradient Method and Its Sufficient Descent Properties”. International Journal of Engineering & Technology, vol. 7, no. 3.28, Aug. 2018, pp. 312-5, https://doi.org/10.14419/ijet.v7i3.28.23467.