In DDPG: Add support for vector actions

[oysteinsolheim]

Currently only scalar actions are supported, how far up on the priority list is it to expand on this?

[findmyway]

I think it's relatively easy to support actions of a vector in DDPG, but the main issue here is that we lack environments with this kind of actions 😰

Do you know any environments that are good testbeds for DDPG with multiple actions? @jbrea

[jbrea]

Do you know any environments that are good testbeds for DDPG with multiple actions?

There is e.g. Mujoco, but I don't have a license.
There are also some environments in Gym (GymEnv in RLEnvironments), e.g. I think most of the bullet envs.
And I think it would also be cool to create some environments with RigidBodySims...
But I don't know right now which environment would be the simplest to just run a couple of tests.

[findmyway]

I may improve existing algorithms to support vector actions in the near future. Ref JuliaReinforcementLearning/ReinforcementLearningZoo.jl#102

Action space We include tasks with both discrete and continuous action spaces, and of varying action
dimension with up to 56 dimensions in the initial release of RL Unplugged.