Expose mj_makeM as a sub-component.

PiperOrigin-RevId: 763662068
Change-Id: I55ced456dca751c1de09fb35e2f73c60ffc0d626

doc/APIreference/functions.rst

@@ -748,8 +748,7 @@ Compare forward and inverse dynamics, save results in fwdinv.
 Sub components
 ^^^^^^^^^^^^^^
 
-These are sub-components of the simulation pipeline, called internally from the components above. It is very unlikely
-that the user will need to call them.
+These are sub-components of the simulation pipeline, called internally from the components above.
 
 .. _mj_sensorPos:
 
@@ -886,6 +885,18 @@ Compute actuator transmission lengths and moments.
 
 Run composite rigid body inertia algorithm (CRB).
 
+.. _mj_makeM:
+
+`mj_makeM <#mj_makeM>`__
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. mujoco-include:: mj_makeM
+
+Compute the composite rigid body inertia with :ref:`mj_crb`, add terms due
+to :ref:`tendon armature<tendon-spatial-armature>`. The joint-space inertia matrix is stored in both ``mjData.qM`` and
+``mjData.M``. These arrays represent the same quantity using different layouts (parent-based and compressed sparse row,
+respectively).
+
 .. _mj_factorM:
 
 `mj_factorM <#mj_factorM>`__

doc/APIreference/functions_override.rst

@@ -113,8 +113,14 @@ Integrates the simulation state using an implicit-in-velocity integrator (either
 
 .. _Subcomponents:
 
-These are sub-components of the simulation pipeline, called internally from the components above. It is very unlikely
-that the user will need to call them.
+These are sub-components of the simulation pipeline, called internally from the components above.
+
+.. _mj_makeM:
+
+Compute the composite rigid body inertia with :ref:`mj_crb`, add terms due
+to :ref:`tendon armature<tendon-spatial-armature>`. The joint-space inertia matrix is stored in both ``mjData.qM`` and
+``mjData.M``. These arrays represent the same quantity using different layouts (parent-based and compressed sparse row,
+respectively).
 
 .. _mj_factorM:
 

doc/XMLreference.rst

@@ -2918,8 +2918,8 @@ Attributes may be applied or ignored depending on the lighting model being used.
 .. _body-light-directional:
 
 :at:`directional`: :at-val:`[false, true], "false"`
-   This is a deprecated legacy attribute. Please use :ref:`light <light-type>` type instead. If set to "true", and no
-   type is specified, this will change the light type to be directional.
+   This is a deprecated legacy attribute. Please use :ref:`light <body-light-type>` type instead. If set to "true", and
+   no type is specified, this will change the light type to be directional.
 
 .. _body-light-castshadow:
 

doc/changelog.rst

@@ -14,6 +14,9 @@ General
 - Replaced the :ref:`directional<body-light-directional>` (boolean) field for lights with a
   :ref:`type<body-light-type>` field (of type :ref:`mjtLightType<mjtLightType>`) to allow for additional lighting
   types.
+- Added new sub-component :ref:`mj_makeM` which combines the :ref:`mj_crb` call with additional logic to support the
+  introduction in 3.3.1 of :ref:`tendon armature<tendon-spatial-armature>`. In addition to the traditional
+  ``mjData.qM``, :ref:`mj_makeM` also computes ``mjData.M``, a CSR representation of the same matrix.
 
 Simulate
 ^^^^^^^^

doc/computation/index.rst

@@ -1692,7 +1692,7 @@ The stages below compute quantities that depend on the generalized positions ``m
 4. Compute quantities related to :ref:`flex<deformable-flex>` objects: :ref:`mj_flex`
 5. Compute the tendon lengths and moment arms. This includes the computation of minimal-length paths for spatial
    tendons: :ref:`mj_tendon`
-6. Compute the composite rigid body inertias and joint-space inertia matrix: :ref:`mj_crb`
+6. Compute the composite rigid body inertias and joint-space inertia matrix: :ref:`mj_makeM`
 7. Compute the sparse factorization of the joint-space inertia matrix: :ref:`mj_factorM`
 8. Construct the list of active contacts. This includes both broad-phase and near-phase collision detection:
    :ref:`mj_collision`

doc/includes/references.h

@@ -267,7 +267,7 @@ struct mjData_ {
   int*    moment_colind;     // column indices in sparse Jacobian                (nJmom x 1)
   mjtNum* actuator_moment;   // actuator moments                                 (nJmom x 1)
 
-  // computed by mj_fwdPosition/mj_crb
+  // computed by mj_fwdPosition/mj_makeM
   mjtNum* crb;               // com-based composite inertia and mass             (nbody x 10)
   mjtNum* qM;                // inertia (sparse)                                 (nM x 1)
   mjtNum* M;                 // reduced inertia (compressed sparse row)          (nC x 1)
@@ -3068,6 +3068,7 @@ void mj_flex(const mjModel* m, mjData* d);
 void mj_tendon(const mjModel* m, mjData* d);
 void mj_transmission(const mjModel* m, mjData* d);
 void mj_crb(const mjModel* m, mjData* d);
+void mj_makeM(const mjModel* m, mjData* d);
 void mj_factorM(const mjModel* m, mjData* d);
 void mj_solveM(const mjModel* m, mjData* d, mjtNum* x, const mjtNum* y, int n);
 void mj_solveM2(const mjModel* m, mjData* d, mjtNum* x, const mjtNum* y,