Sampled Differential Dynamic Programming

We present SaDDP, a sampled version of the widely used differential dynamic programming (DDP) control algorithm. We contribute through establishing a novel connection between two major branches of robotics control research, that is, gradient-based methods such as DDP, and Monte Carlo methods such as path integral control (PI) that utilize random simulated trajectory rollouts. One of our key observations is that the Taylor-expansion, central to DDP, can be reformulated in terms of second-order statistics computed of the sampled trajectories. SaDDP makes few assumptions about the controlled system and works with black-box dynamics simulations with non-smooth contacts. Our simulation results show that the method outperforms PI and CMA-ES in both a simple linear-quadratic problem, and a multilink arm reaching task with obstacles.