1. Function minimization by conjugate gradients
2. E. Polak, and G. Ribiere, Revue Françoise Informant, Reserche Opertionelle 16, 35–43 (1969).
3. Methods of conjugate gradients for solving linear systems
4. Y. Liu and C. Storey, J. Comput. Appl. Math. 69, pp. 129–137 (1992).
5. R. Fletcher, Practical Method of Optimization, Vol. 1: Unconstrained Optimization (John Wiley & Sons, New York, 1987).