  This paper introduces DiffTOP, which utilizes Differentiable Trajectory
OPtimization as the policy representation to generate actions for deep
reinforcement and imitation learning. Trajectory optimization is a powerful and
widely used algorithm in control, parameterized by a cost and a dynamics
function. The key to our approach is to leverage the recent progress in
differentiable trajectory optimization, which enables computing the gradients
of the loss with respect to the parameters of trajectory optimization. As a
result, the cost and dynamics functions of trajectory optimization can be
learned end-to-end. DiffTOP addresses the ``objective mismatch'' issue of prior
model-based RL algorithms, as the dynamics model in DiffTOP is learned to
directly maximize task performance by differentiating the policy gradient loss
through the trajectory optimization process. We further benchmark DiffTOP for
imitation learning on standard robotic manipulation task suites with
high-dimensional sensory observations and compare our method to feed-forward
policy classes as well as Energy-Based Models (EBM) and Diffusion. Across 15
model-based RL tasks and 35imitation learning tasks with high-dimensional image
and point cloud inputs, DiffTOP outperforms prior state-of-the-art methods in
both domains.
