Concept

Support 𝑓 is unimodal on [𝑎,𝑏] and let 𝑥1,𝑥2 two points within [𝑎,𝑏] where 𝑥1<𝑥2.
Discard [𝑎,𝑥1) or (𝑥2,𝑏] depend on 𝑓(𝑥1)>𝑓(𝑥2) or opposite.
Repeat this process.

Cost

convergence rate is only linear, with constant 𝐶0.618.