:term:`CFOUR_UPDATE_HESSIAN <CFOUR_UPDATE_HESSIAN (CFOUR)>`
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

      Specifies whether or not the Hessian update is carried out. OFF (= 0) uses the initial Hessian (however supplied, either the default guess or a ``FCMINT`` file), ON (= 1) updates it during subsequent optimization cycles. (not in current public version).

      * **Type**: :ref:`boolean <op_c_boolean>`
      * **Default**: true