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Iterative algorithm with structured diagonal Hessian approximation for solving nonlinear least squares problems

Nonlinear least-squares problems are a special class of unconstrained optimization problems in which their gradient and Hessian have special structures. In this paper, we exploit these structures and proposed a matrix-free algorithm with a diagonal Hessian approximation for solving nonlinear least-squares problems. We devise appropriate safeguarding strategies to ensure the Hessian matrix is positive definite throughout the iteration process. The proposed algorithm generates descent direction and is globally convergent. Preliminary numerical experiments show that the proposed method is competitive with a recently developed similar method.