As with other NDF components, the history component has a state, which is represented by one of the two values .TRUE. or .FALSE.. If the state is .FALSE., the history component is not defined, and the NDF contains no history information and no reference can be made to its history component. However, if the state is .TRUE., then the history component is defined and enquiries can be made about it. In this case, history records may also be present which describe the past processing history of the NDF. If it is a new NDF, however, it is possible that no such records may yet have been written to the history component.
The state of an NDF's history component can be determined using the NDF_STATE routine by specifying a component name of `History', thus:
CALL NDF_STATE( INDF, 'History', STATE, STATUS )
The state information is returned via the LOGICAL argument STATE.