This paper is concerned with computing -eigenpairs of symmetric tensors.We first show that computing -eigenpairs of a symmetric tensor is equivalent to finding the nonzero solutions of a nonlinear system of equations, and then propose a modified normalized Newton method (MNNM) for it. Our proposed MNNM method is proved to be locally and cubically convergent under some suitable conditions, which greatly improves the Newton correction method and the orthogonal Newton correction method recently provided by Jaffe, Weiss and Nadler since these two methods only enjoy a quadratic rate of convergence. As an application, the unitary symmetric eigenpairs of a complex-valued symmetric tensor arising from the computation of quantum entanglement in quantum physics are calculated by the MNNM method. Some numerical results are presented to illustrate the efficiency and effectiveness of our method.
K E Y W O R D S-eigenpairs, US-eigenpairs, cubical convergence, modified normalized Newton method, Newton correction method, symmetric tensors
INTRODUCTIONThe eigenvalue problems of tensors have attracted much attention in recent years because of their applications in high-order Markov chains, 1 magnetic resonance imaging, 2 quantum entanglement, 3,4 automatical control, 5 the best rank-one approximations in statistical data analysis, 6-10 learning binary latent variable models, 11 and so on. Unlike matrices, there are various definitions of eigenvalues for tensors, including -eigenvalues, -eigenvalues, and -eigenvalues; see, for example, other works 12-18 and the references therein. In this paper, we are mainly concerned with the calculation of -eigenvalues and corresponding -eigenvectors. This kind of eigenvalues and eigenvectors has practical applications, for example, the smallest -eigenvalue can reflect the stability of a nonlinear autonomous system in automatic control, and the principal -eigenvector can depict the orientations of nerve fibers in the voxel of white matter of human brain. 5,19 Computing -eigenpairs of a third or higher order tensor is equivalent to finding nontrivial solutions of a system of inhomogeneous polynomial equations in several variables. This implies that the task in the computation of -eigenpairs of a tensor will be much more difficult when its order and dimension are very large. For this reason, some iterative methods have been developed to compute one or more -eigenpairs of the tensors with special structure, such as nonnegative tensors and symmetric tensors.Recently, for nonnegative tensors, Guo et al. 20 proposed a modified Newton iteration to compute some nonnegative -eigenpairs and showed that this method has local quadratic convergence under appropriate assumptions. Kuo et al. 21 presented a homotopy continuation method for the same purpose. For symmetric tensors, Cui, Dai and Numer Linear Algebra Appl. 2020;27:e2284.wileyonlinelibrary.com/journal/nla