👉 Ishikawa's theorem is a result in functional analysis that establishes a connection between the spectrum of linear operators and the behavior of their eigenvalues. It states that if an operator on a finite-dimensional Hilbert space has a single-valued, continuous spectrum, then its adjoint operator also has a single-valued, continuous spectrum. This theorem provides a framework for understanding the behavior of linear operators in infinite dimensions, particularly in the study of dissipative and singular perturbation problems.
