[Model] Add time derivative quantity of the joint Jacobian J

bindings/python/multibody/data.hpp

@@ -83,6 +83,7 @@ namespace se3
         .ADD_DATA_PROPERTY(std::vector<int>,parents_fromRow,"First previous non-zero row in M (used in Cholesky)")
         .ADD_DATA_PROPERTY(std::vector<int>,nvSubtree_fromRow,"")
         .ADD_DATA_PROPERTY_READONLY_BYVALUE(Matrix6x,J,"Jacobian of joint placement")
+        .ADD_DATA_PROPERTY_READONLY_BYVALUE(Matrix6x,dJ,"Time variation of the Jacobian of joint placement (data.J).")
         .ADD_DATA_PROPERTY(container::aligned_vector<SE3>,iMf,"Body placement wrt to algorithm end effector.")
         
         .ADD_DATA_PROPERTY_READONLY_BYVALUE(Matrix6x,Ag,

src/multibody/model.hpp

@@ -456,6 +456,9 @@ namespace se3
     /// \note The columns of J corresponds to the basis of the spatial velocities of each joint and expressed at the origin of the inertial frame. In other words, if \f$ v_{J_{i}} = S_{i} \dot{q}_{i}\f$ is the relative velocity of the joint i regarding to its parent, then \f$J = \begin{bmatrix} ^{0}X_{1} S_{1} & \cdots & ^{0}X_{i} S_{i} & \cdots & ^{0}X_{\text{nj}} S_{\text{nj}} \end{bmatrix} \f$. This Jacobian has no special meaning. To get the jacobian of a precise joint, you need to call se3::getJacobian
     Matrix6x J;
     
+    /// \brief Derivative of the Jacobian with respect to the time.
+    Matrix6x dJ;
+    
     /// \brief Vector of joint placements wrt to algorithm end effector.
     container::aligned_vector<SE3> iMf;
 

src/multibody/model.hxx

@@ -252,6 +252,7 @@ namespace se3
     ,parents_fromRow((std::size_t)model.nv)
     ,nvSubtree_fromRow((std::size_t)model.nv)
     ,J(6,model.nv)
+    ,dJ(6,model.nv)
     ,iMf((std::size_t)model.njoints)
     ,com((std::size_t)model.njoints)
     ,vcom((std::size_t)model.njoints)