- Add private function `mj_arenaAlloc`. This is used internally to allocate memory from the arena.
- Add private function `mj_nefc` to count constraints. This function returns a tight upper bound on `d->nefc`. The number of counted constraints can be slightly bigger than exact `d->nefc` in the case of constraints with empty Jacobian, as when placing a frictional tendon between two world sites.
- Add new `memory` attribute to the `size` XML element for specification of arena memory size. This attribute is mutually exclusive with `nstack` and `njmax` specifications, which are now deprecated (but left around for the time being for legacy compatibility).
- Move `d->stack` to the end of the new arena space. The stack now grows in reverse from the end.
PiperOrigin-RevId: 479341539
Change-Id: Ie019c202e0908577ffc6f833a37920858116f667
- Add `qH` and `qHDiagInv` to `mjData` to save factorized modified inertia.
- Add `mj_EulerSkip`, `mj_implicitSkip`, to `engine_forward.c`.
- Using the above functions, implement `mj_stepSkip` in `engine_derivative.c`.
- Add `mjd_stepFD` and `mjd_transitionFD` to `engine_derivative.c` to compute `mj_step` Jacobians.
- Exploit "Skip" functionality for speed.
- Correctly handle quaternion derivatives.
- Handle warmstarts and control limits.
PiperOrigin-RevId: 456584811
Change-Id: Iee8541f11e7b66feb8f431cb102d9bbe65461f79
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
Yuval Tassa