“…for which f : R n −→ R is a continuously differentiable function and bounded from below. There are many kinds of iterative methods to solve unconstrained optimization problems including the Newton method [28], the steepest descent method [29], the conjugate gradient methods [11,13,16,23], the quasi-Newton methods [9,[18][19][20], line search methods [9,22] and trust-region methods [26,34,37,40]. Conjugate gradient methods [13,16,22,24,30] are the powerful classes of iterative methods to solve unconstrained optimization problems, which are suitable especially for the large-scale problems due to the simplicity of their iterates and low memory requirements.…”