When an NDF is first created, all its components start out in an undefined state and they become defined only when values have been assigned to them. Note that with the exception of the history component (see §), there is no separate concept of component ``creation'' in the NDF_ system - i.e. there is no need to ``create'' a component before assigning a value to it, and a component cannot ``exist'' without also having a value. The method by which values are assigned depends on the individual component, and is discussed in later sections.
The opposite process, i.e. of resetting a component to become undefined, is more straightforward and is the same for all components. It is performed by the routine NDF_RESET, which takes the name of a component or a list of components in the same way as NDF_STATE. For example:
CALL NDF_RESET( INDF, 'Data,Variance,Units', STATUS )
would reset the state of the three named components, making their values
unavailable and therefore effectively erasing them.