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erwincoumans / tiny-differentiable-simulator

Tiny Differentiable Simulator is a header-only C++ and CUDA physics library for reinforcement learning and robotics with zero dependencies.
Apache License 2.0
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The effect of accelerations on the velocities is added twice #200

Closed jotix16 closed 2 years ago

jotix16 commented 2 years ago

Considering the example in ant_environment.h or laikago_environment.h, the Semi-Implicit-Euler integration takes place in the following snippet

https://github.com/erwincoumans/tiny-differentiable-simulator/blob/c1a9e06de33756bceacfaddeecc6bc4b6c98560c/examples/environments/ant_environment.h#L196-L200

First integrate_euler_qdd(*mb_, dt); is called to add the effect of accelerations into change of velocities, then tds::integrate_euler(*mb_, dt); is called to integrate once again.

But if we look into integrator.hpp, we find the integration of acceleration on both functions, i.e in integrate_euler(..):

https://github.com/erwincoumans/tiny-differentiable-simulator/blob/c1a9e06de33756bceacfaddeecc6bc4b6c98560c/src/dynamics/integrator.hpp#L95-L98

and in integrate_euler_qdd(..) https://github.com/erwincoumans/tiny-differentiable-simulator/blob/c1a9e06de33756bceacfaddeecc6bc4b6c98560c/src/dynamics/integrator.hpp#L173-L175

Is this meant to be like this or is this an error and it should be taken care of?

erwincoumans commented 2 years ago

The accelerations should be cleared to zero after 'integrate_euler_qdd', isn't it?

  Algebra::set_zero(mb.qdd());
jotix16 commented 2 years ago

Missed that one. Thank you, I am closing the issue.