/// \brief Vector of subtree mass. In other words, mass[j] is the mass of the subtree supported by joint \f$ j \f$. The element mass[0] corresponds to the total mass of the model.
std::vector<Scalar>mass;
/// \brief Jacobien of center of mass.
/// \brief Jacobian of center of mass.
/// \note This Jacobian maps the joint velocity vector to the velocity of the center of mass, expressed in the inertial frame. In other words, \f$ v_{\text{CoM}} = J_{\text{CoM}} \dot{q}\f$.
