GEW ZGV computation

Compute zero-group-velocity (ZGV) points of guided elastic waves (GEWs).

Three different computational techniques to locate ZGV points on dispersion curves are implemented. They are all based on the discretized waveguide problem.

• Newton-type iteration: super fast but needs initial guesses.
• Method of fixed relative distance (MFRD): scans a wavenumber interval without initial guesses and is likely to locate all ZGV points but is substantially slower. It refines computed approximations with the Newton-type iteration.
• Direct method: does not need initial guesses and guarantees to find all ZGV points. It is slow and can, therefore, only be used with rather small matrices.