M Said Alghabra authored Aug 02, 2023 and David Frank committed Aug 02, 2023

This commits adds an interface for line search methods and implements 
a couple of important algorithms. These include versions based on the
Armijo, Strong Wolfe, and Goldstein condition, and Barzilai-Borwein.

Line search methods can be an important condition to improve convergence,
and be necessary for certain types of solvers such as BFGS.

A future commit will integrate these line search methods into the
gradient-based solvers.