Rename C sparse structure to M in mjdata, improve docstrings.

PiperOrigin-RevId: 758636638
Change-Id: If78acc423601d2911f514929b27f7b6d0af9ef58

mjx/mujoco/mjx/_src/io.py

@@ -629,10 +629,10 @@ def _make_data_c(
       'B_rownnz': (m.nbody, np.int32),
       'B_rowadr': (m.nbody, np.int32),
       'B_colind': (m.nB, np.int32),
-      'C_rownnz': (m.nv, np.int32),
-      'C_rowadr': (m.nv, np.int32),
-      'C_colind': (m.nC, np.int32),
-      'mapM2C': (m.nC, np.int32),
+      'M_rownnz': (m.nv, np.int32),
+      'M_rowadr': (m.nv, np.int32),
+      'M_colind': (m.nC, np.int32),
+      'mapM2M': (m.nC, np.int32),
       'D_rownnz': (m.nv, np.int32),
       'D_rowadr': (m.nv, np.int32),
       'D_diag': (m.nv, np.int32),

mjx/mujoco/mjx/_src/smooth_test.py

@@ -92,7 +92,7 @@ class SmoothTest(absltest.TestCase):
     dx = jax.jit(mjx.factor_m)(mx, mjx.put_data(m, d))
     qLDLegacy = np.zeros(mx.nM)  # pylint:disable=invalid-name
     for i in range(m.nC):
-      qLDLegacy[d.mapM2C[i]] = d.qLD[i]
+      qLDLegacy[d.mapM2M[i]] = d.qLD[i]
     _assert_eq(qLDLegacy, dx._impl.qLD, 'qLD')
     _assert_attr_eq(d, dx._impl, 'qLDiagInv')
     # com_vel

mjx/mujoco/mjx/_src/types.py

@@ -985,10 +985,10 @@ class DataC(PyTreeNode):
   B_rownnz: jax.Array  # pylint:disable=invalid-name
   B_rowadr: jax.Array  # pylint:disable=invalid-name
   B_colind: jax.Array  # pylint:disable=invalid-name
-  C_rownnz: jax.Array  # pylint:disable=invalid-name
-  C_rowadr: jax.Array  # pylint:disable=invalid-name
-  C_colind: jax.Array  # pylint:disable=invalid-name
-  mapM2C: jax.Array  # pylint:disable=invalid-name
+  M_rownnz: jax.Array  # pylint:disable=invalid-name
+  M_rowadr: jax.Array  # pylint:disable=invalid-name
+  M_colind: jax.Array  # pylint:disable=invalid-name
+  mapM2M: jax.Array  # pylint:disable=invalid-name
   D_rownnz: jax.Array  # pylint:disable=invalid-name
   D_rowadr: jax.Array  # pylint:disable=invalid-name
   D_diag: jax.Array  # pylint:disable=invalid-name