void realizeInstance(const SBStateDigest& sbs) const {
// Initialize cache entries that will never be changed at later stages.
SBTreeVelocityCache& vc = sbs.updTreeVelocityCache();
SBDynamicsCache& dc = sbs.updDynamicsCache();
SBTreeAccelerationCache& ac = sbs.updTreeAccelerationCache();
updY(dc) = SpatialMat(Mat33(0));
updA_GB(ac) = 0;
}
void realizeDynamics(const SBArticulatedBodyInertiaCache& abc,
const SBStateDigest& sbs) const {
// Mobilizer-specific.
const SBTreePositionCache& pc = sbs.getTreePositionCache();
const SBTreeVelocityCache& vc = sbs.getTreeVelocityCache();
SBDynamicsCache& dc = sbs.updDynamicsCache();
// Mobilizer independent.
calcJointIndependentDynamicsVel(pc,abc,vc,dc);
}