Efficient computation of high index Sturm-Liouville eigenvalues for problems in physics
This work provides efficient numerical methods for physicists and engineers who need to compute many eigenvalues of Sturm-Liouville problems, reducing computational cost.
The paper addresses the computational challenge of computing high-index eigenvalues in Sturm-Liouville problems, which becomes difficult due to oscillatory solutions. It presents coefficient approximation methods combined with Magnus or Neumann integrators that achieve uniform accuracy across the spectrum, enabling large step sizes even for high eigenvalues.
Finding the eigenvalues of a Sturm-Liouville problem can be a computationally challenging task, especially when a large set of eigenvalues is computed, or just when particularly large eigenvalues are sought. This is a consequence of the highly oscillatory behaviour of the solutions corresponding to high eigenvalues, which forces a naive integrator to take increasingly smaller steps. We will discuss some techniques that yield uniform approximation over the whole eigenvalue spectrum and can take large steps even for high eigenvalues. In particular, we will focus on methods based on coefficient approximation which replace the coefficient functions of the Sturm-Liouville problem by simpler approximations and then solve the approximating problem. The use of (modified) Magnus or Neumann integrators allows to extend the coefficient approximation idea to higher order methods.