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.