On Some Applications of Lidskii's Theorem

Lidskii's theory is considered one of the most important and recent theories for calculating the following categories and the relationship between them and the eigenvalues. This theory provides an easier way to prove the existence of the eigenvalues, and hence to prove the existence of solutions for some kind of problems. This thesis article to prove that there are solutions to some problems for which the computation of eigenvalues is very complex and to prove that the existence of eigenvalues is also complex, in our work we try to take advantage of the fact that calculating the trace is much easier than calculating eigenvalues. Lidskii's theorem gives the relationship between Trace and eigenvalues and gives us a way to prove the existence of eigenvalues.

Almost Exact Computation of Eigenvalues in Approximate Differential Problems

Differential eigenvalue problems arise in many fields of Mathematics and Physics, often arriving, as auxiliary problems, when solving partial differential equations. In this work, we present a method for eigenvalues computation following the Tau method philosophy and using Tau Toolbox tools. This Matlab toolbox was recently presented and here we explore its potential use and suitability for this problem. The first step is to translate the eigenvalue differential problem into an algebraic approximated eigenvalues problem. In a second step, making use of symbolic computations, we arrive at the exact polynomial expression of the determinant of the algebraic problem matrix, allowing us to get high accuracy approximations of differential eigenvalues.