Gradient and diagonal Hessian approximations using quadratic interpolation models and aligned regular bases

Abstract

This work investigates finite differences and the use of (diagonal) quadratic interpolation models to obtain approximations to the first and (non-mixed) second derivatives of a function. Here, it is shown that if a particular set of points is used in the interpolation model, then the solution to the associated linear system (i.e., approximations to the gradient and diagonal of the Hessian) can be obtained in $\mathcal {O}(n)$ computations, which is the same cost as finite differences, and is a saving over the $\mathcal {O}(n^{3})$ cost when solving a general unstructured linear system. Moreover, if the interpolation points are chosen in a particular way, then the gradient approximation is $\mathcal {O}(h^{2})$ accurate, where h is related to the distance between the interpolation points. Numerical examples confirm the theoretical results.