Hi, itkMatrix has been reworked. it doesn't derive from vnl_matrix_fixed anymore, now it contains a vnl_matrix_fixed. The product operations are defined for : - itkPoint - itkVector - itkCovariantVector - itkMatrix - vnl_matrix - vnl_vector Access to the internal vnl_matrix can be get through GetVnlMatrix(). it can be initalized with SetIdentity(); and accept assigments from itkMatrix vnl_matrix Luis