Approximation Theory and Approximation Practice

Approximation Theory is VERY old, and engineers from decades ago used to struggle with it. Analytic, stochastic, and qualitative methods were well traveled areas until the dawn of numerics, NP computing theory, etc.

It covers a lot aspects of appr theory, while still keep understandable for most people with undergraduate math. It also includes a lot of examples for how use chebfun.