Golden Section Search

Concept

Support $f$ is unimodal on $[a,b]$ and let $x_1,x_2$ two points within $[a,b]$ where $x_1<x_2$.
Discard $[a,x_1)$ or $(x_2,b]$ depend on $f(x_1)>f(x_2)$ or opposite.
Repeat this process.

Cost

convergence rate is only linear, with constant $C\approx 0.618$.