SNESLINESEARCHL2#

Secant search in the L2 norm of the function or the objective function, if it is provided with SNESSetObjective(). Attempts to solve $\min_{\lambda} f(x + \lambda y)$ using the secant method with the initial bracketing of $\lambda$ between [0,damping]. Differences of $f()$ are used to approximate the first and second derivative of $f()$ with respect to $\lambda$, $f'()$ and $f''()$. The secant method is run for maxit iterations.

When an objective function is provided $f(w)$ is the objective function otherwise $f(w) = ||F(w)||^2$. $x$ is the current step and $y$ is the search direction.

This has no checks on whether the secant method is actually converging.