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Add implicit integrator.

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Added analytic derivatives of smooth (unconstrained) dynamics forces, with respect to velocities:
  - Centripetal and Coriolis forces computed by the Recursive Newton-Euler algorithm.
  - Damping and fluid-drag passive forces.
  - Actuation forces.

A new implicit-in-velocity integrator is implemented using the analytic derivatives. This integrator lies between the Euler and Runge Kutta integrators in terms of both stability and computational cost.

PiperOrigin-RevId: 450377010
Change-Id: Ie192b441876c22e732fb749333926f296e0a09cc
This commit is contained in:
DeepMind
2022-05-23 01:21:24 -07:00
committed by Copybara-Service
parent 1913a02b40
commit 64bc6d27b2
30 changed files with 1974 additions and 51 deletions
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test/engine/testdata/derivative/energy_conserving_pendulum.xml
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<mujoco>
<option integrator="implicit">
<flag constraint="disable" energy="enable"/>
</option>
<worldbody>
<light pos="0 0 1"/>
<geom type="plane" size="1 1 .01" pos="0 0 -1"/>
<body pos="0.15 0 0">
<joint type="hinge" axis="0 1 0"/>
<geom type="capsule" size="0.02" fromto="0 0 0 .1 0 0"/>
<body pos="0.1 0 0">
<joint type="slide" axis="1 0 0" stiffness="200"/>
<geom type="capsule" size="0.015" fromto="-.1 0 0 .1 0 0"/>
<body pos=".1 0 0">
<joint type="ball"/>
<geom type="box" size=".02" fromto="0 0 0 0 .1 0"/>
<body pos="0 .1 0">
<joint axis="1 0 0"/>
<geom type="capsule" size="0.02" fromto="0 0 0 0 .1 0"/>
</body>
</body>
</body>
</body>
</worldbody>
</mujoco>