But === The purpose of the operator is to define: * the basis for dynamic substructuring, when the complete structure has been divided into substructures; * or the basis for modal recombination, when the complete structure is treated directly. The modal base obtained by this operator is of the type: 'CLASSIQUE' if the modal base is composed of dynamic eigenmodes and static deformations calculated by the operator from an interfer_dyna_clas concept produced by DEFI_INTERF_DYNA [:ref:`U4.64.01 `]. Option DIAG_MASS allows you to recalculate a numbering for static modes so that the mass matrix is diagonal. The base is of type RITZ in the other cases. The operator produces a mode_meca concept.