Implicitfast integration for MJX.

PiperOrigin-RevId: 664889120
Change-Id: Id3bd3916fe821ab2af79c52e53e14837ae829b2a

doc/changelog.rst

@@ -23,17 +23,19 @@ MJX
 7. Added velocity-dependent sensors: ``JOINTVEL``, ``ACTUATORVEL``, ``BALLANGVEL``.
 8. Changed default policy to avoid placing unused (MuJoCo-only) arrays on device.
 9. Added ``device`` parameter to ``mjx.make_data`` to bring it to parity with ``mjx.put_model`` and ``mjx.put_data``.
+10. Added support for :ref:`implicitfast integration<geIntegration>` for all cases except
+    :doc:`fluid drag <computation/fluid>`.
 
 Bug fixes
 ^^^^^^^^^
-10.  Fixed a performance regression introduced in 3.1.7 in mesh Bounding Volume Hierarchies (:github:issue:`1875`,
+11. Fixed a performance regression introduced in 3.1.7 in mesh Bounding Volume Hierarchies (:github:issue:`1875`,
     contribution by :github:user:`michael-ahn`).
-11. Fixed a bug wherein, for models that have both muscles and stateless actuators and used one of the implicit
+12. Fixed a bug wherein, for models that have both muscles and stateless actuators and used one of the implicit
     integrators, wrong derivatives would be computed.
 
 Python bindings
 ^^^^^^^^^^^^^^^
-12. Added support for engine plugins in :ref:`mjSpec` (:github:issue:`1903`).
+13. Added support for engine plugins in :ref:`mjSpec` (:github:issue:`1903`).
 
 
 Version 3.2.2 (Aug 8, 2024)

doc/mjx.rst

@@ -202,7 +202,7 @@ The following features are **fully supported** in MJX:
    * - :ref:`Equality <mjtEq>`
      - ``CONNECT``, ``WELD``, ``JOINT``, ``TENDON``
    * - :ref:`Integrator <mjtIntegrator>`
-     - ``EULER``, ``RK4``
+     - ``EULER``, ``RK4``, ``IMPLICITFAST`` (``IMPLICITFAST`` not supported with :doc:`fluid drag <computation/fluid>`)
    * - :ref:`Cone <mjtCone>`
      - ``PYRAMIDAL``, ``ELLIPTIC``
    * - :ref:`Condim <coContact>`
@@ -229,7 +229,7 @@ The following features are **in development** and coming soon:
    * - :ref:`Constraint <mjtConstraint>`
      - :ref:`Frictionloss <coFriction>`, ``FRICTION_DOF``
    * - :ref:`Integrator <mjtIntegrator>`
-     - ``IMPLICIT``, ``IMPLICITFAST``
+     - ``IMPLICIT``
    * - Dynamics
      - :ref:`Inverse <mj_inverse>`
    * - :ref:`Actuator Dynamics <mjtDyn>`