equilibrateMuscles() not called in osim.py?

[fwillett]

I think that equilibrateMuscles() should be called in osim.py when initializing the simulation? I noticed it wasn't being called and, when I added it, it helped some of our reaching simulations a lot by fixing bad startup behavior in the muscles.

I think it needs to be called in OsimModel's init function like this (at the end):

    state = self.model.initSystem()
    self.model.equilibrateMuscles(state)

and in reset() like this (at the beginning):

    self.state = self.model.initializeState()
    self.model.equilibrateMuscles(self.state)

[kidzik]

Thanks! Indeed that might affect the starting point, we will revise that in the upcoming release.

[adwardlee]

Is it necessary to add this function? I think it was not used in the competition last year either?

[carmichaelong]

It wasn't used in last year's version, but it's more important this year because the dictionary has information about the muscle states, such as fiber length and force, which may change greatly during startup due to equilibrateMuscles(). Furthermore, it brings the first step in the simulation more in line with the rest of the simulation, since equilibrateMuscles() is inherently called with each integration step.

[AdamStelmaszczyk]

@kidzik When this will be fixed?

[kidzik]

This is a minor issue (affecting only the first step of the simulation) which will be fixed most likely in the second round.

[AdamStelmaszczyk]

It's not that minor as it seems, many algorithms calculate mean and standard deviation of the observations to normalize the input. It's broken when the values in the first step are huge.

[kidzik]

We run equilibrateMuscles now in the reset function https://github.com/stanfordnmbl/osim-rl/blob/master/osim/env/osim.py#L237