https://se.mathworks.com/help/control/ref/frdmodel.abs.html
abs - Entrywise magnitude of frequency response - MATLAB
This MATLAB function computes the magnitude of the frequency response contained in the FRD model sys.
frequency responseabsmagnitudematlab
https://arxiv.org/abs/2405.14494v1
[2405.14494v1] Entrywise error bounds for low-rank approximations of kernel matrices
Abstract page for arXiv paper 2405.14494v1: Entrywise error bounds for low-rank approximations of kernel matrices