Access underlying dynamics function

[theophilegervet]

Hi,

How could we access the dynamics function of an environment? Given arbitrary state and action, I would like to retrieve the function used to compute the next state (without going through env.step()).

I'm trying to run the cross-entropy method with the true dynamics, but currently I have to duplicate the environment and use step() to propagate my particles. This is super slow and it would be much more convenient to be able to do this in parallel with the dynamics function.

Thank you very much!

[christopherhesse]

You should be able to get these for the toy environments, since they have the transition probabilities. For more advanced environments, some sort of get_state()/set_state() seems the most doable, and is unlikely to be terribly fast.

I think it's unlikely that we'll be able to provide anything better than get_state()/set_state() for most environments, and we don't even support that for most environments currently: #402