Preparing to Record History Information

Unlike other NDF components, the history component does not become defined simply by writing to it (i.e. by the act of recording new history information). This is because recording of history information is not always required. It can, for instance, lead to the use of large amounts of file space or of additional processing time which is not justified, so resetting the history component (setting its state to .FALSE. - see §) provides the user of an application with one way of disabling history recording when it is not required. In general, one does not want this action negated by the next application which attempts to record further history information.

Before history information can be recorded in an NDF, it is therefore necessary to explicitly define a history component to receive it. The NDF_HCRE routine will perform this, as follows:

      CALL NDF_HCRE( INDF, STATUS )

NDF_HCRE will return without error if a history component is already defined. Otherwise, it will initialise a new one, making the NDF receptive to new history records (although there will initially be none of these present).

In addition, if the ``NDF_AUTO_HISTORY'' environment variable or ``AUTO_HISTORY'' tuning parameter is set to a non-zero integer (see NDF_TUNE), then a History component will be added automatically to NDFs created using either NDF_CREAT or NDF_NEW.