gradient ascent simulation-based optimization robotics local search
under mild conditions this function will be differentiable as a function of the parameter vector 



θ


{\displaystyle \theta }

. If the gradient of 



ρ


{\displaystyle \rho }

 was known, one could use gradient ascent. Since an analytic expression for the gradient is not available, only a noisy estimate is available. Such an estimate can be constructed in many ways, giving rise to algorithms such as Williams' REINFORCE method (which is known as the likelihood ratio method in the simulation-based optimization literature). Policy search methods have been used in the robotics context. Many policy search methods may get stuck in local optima (as they are based on local search).
