Two efficient spectral hybrid CG methods based on memoryless BFGS direction and Dai–Liao conjugacy condition

The spectral conjugate gradient (CG) method is one of the effective methods for solving unconstrained optimization problems. In this work, we introduce a composite hybrid CG parameter which is a convex combination of two new adaptive hybrid CG parameters. To derive the optimal choice of the combination coefficient in our proposed composite CG parameter, two approaches to calculating it are introduced. One is to minimize the distance between the hybrid CG direction and the self-scaling memoryless BFGS direction and the other is to apply the Dai–Liao conjugacy condition. Further, to make the search direction have better theoretical performance, two effective spectral hybrid CG methods are generated. Our proposed methods ensure the sufficient descent property regardless of the line search. And the global convergence results for general non-convex functions are established under some fundamental assumptions and Wolfe line search. Numerical experiments on solving unconstrained optimization problems illustrate the effectiveness of our proposed methods.