“…However, it is imperative to recognize that while the pure Newton method is restricted to local convergence and lacks the ability to discern between local minima, maxima, and saddle points, the trustregion algorithm demonstrates a more resilient behavior, as evidenced by Absil et al (2007), ensuring convergence to stationary points irrespective of initial conditions. Since optimization on a compact manifold can be conceptualized as a general nonlinear optimization problem with constraints, the extension of the trust-region algorithm from Euclidean space to manifold settings has been a subject of direct pursuit and extensive investigation, yielding successful applications (Absil et al, 2004(Absil et al, , 2007Baker et al, 2008;Boumal and Absil, 2011;Heidel and Schulz, 2018;Ishteva et al, 2011;Li et al, 2021;Sato, 2015;Sato and Sato, 2018;Yang et al, 2019;Zhang, 2012). Particularly noteworthy is the Riemannian trust-region (RTR) approach proposed by Ishteva et al (2011) for achieving the best rank-(R 1 , R 2 , R 3 ) approximation of third-order tensors, a problem framed as the minimization of a cost function over a product of three Grassmann manifolds.…”