Rename efc_diagApprox -> efc_diagA.

The field now stores either an approximate or exact diagonal of the constraint matrix A, so the name is made more general.

PiperOrigin-RevId: 924244954
Change-Id: I62b2f76531fb88b7b3bf96e6769940197596702b

doc/changelog.rst

@@ -28,6 +28,10 @@ General
        (multi-threaded). The island-specific matrices ``iM, iLD, iefc_J`` were removed from the arena and are now
        allocated on the stack.
 
+     - Following the introduction of the :ref:`diagexact<option-flag-diagexact>` flag, the ``mjData`` field
+       ``efc_diagApprox`` was renamed to ``efc_diagA``, as it can now be either the exact or approximate diagonal of
+       the :math:`A` ("Delassus") matrix.
+
 Bug fixes
 ^^^^^^^^^
 - Fixed a bug in the ``mjz`` :ref:`decoder <mjpDecoder>` where unnormalized paths would fail to be read.

doc/includes/references.h

@@ -318,7 +318,7 @@ struct mjData_ {
   mjtNum* efc_pos;           // constraint position (equality, contact)          (nefc x 1)
   mjtNum* efc_margin;        // inclusion margin (contact)                       (nefc x 1)
   mjtNum* efc_frictionloss;  // frictionloss (friction)                          (nefc x 1)
-  mjtNum* efc_diagApprox;    // approximation to diagonal of A                   (nefc x 1)
+  mjtNum* efc_diagA;         // diagonal of A matrix, approximate or exact       (nefc x 1)
   mjtNum* efc_KBIP;          // stiffness, damping, impedance, imp'              (nefc x 4)
   mjtNum* efc_D;             // constraint mass                                  (nefc x 1)
   mjtNum* efc_R;             // inverse constraint mass                          (nefc x 1)