Distinct eigenvalues, Perturbation, Geometric multiplicity, Algebraic multiplicity
In 2016, Farrell presented an upper bound for the number of distinct eigenvalues of a perturbed matrix. Xu (2017), and Wang and Wu (2016) introduced upper bounds which are sharper than Farrell's bound. In this paper, the upper bounds given by Xu, and Wang and Wu are improved.
Moon, Sunyo and Park, Seungkook.
"Upper Bound for the Number of Distinct Eigenvalues of a Perturbed Matrix",
Electronic Journal of Linear Algebra,
Volume 34, pp. 115-124.