Process flow split points
define positions in the flow where
variations in parameter values or process steps occur. Recomputing new
experiments only from split points on is a powerful strategy to
minimize the total computational effort and to yield results more
quickly. Split points are generated by comparing runs to be submitted
against the split tree of all existing runs of a given process and
determining the most similar one that contains valid output data.
Comparison is based on
the complete tool parameter set actually used to invoke the tool
rather than a potentially incomplete - with respect to the
computation of output data - specification of process
steps.
Figure 6.2 shows three runs with parameter modification
at the second and the third step. As the specifications - and thus the
results - of the first steps of all runs and of the second steps of
runs two and three are identical, they need not be computed.
Split points are defined to reflect the flow of data taking place.
Figure 6.2:
Reduction of total computation by splitting.
Splitting avoids recomputation of results
that remain unchanged across different runs.
When comparing step parameter sets, the numerical accuracy of the
comparison has to be limited to an appropriate relative difference,
i.e., two floating point numbers are treated as equal when their
relative difference is smaller that a given number. In VISTA/SFC,
this epsilon is adjustable by the user (see
Figure 6.1), a value of 
has proven to be
well-suited for most applications.