Later
Assumptions made about artifacts later than those in the data can greatly influence the outcome of any seriation. Feature values for later artifacts are essentially blank and like blanks it is not always obvious how to interpret them. We could assume that later feature values are simply unknown, or we could assume that a feature is absent for later artifacts or we could assume that the feature value is zero. Whatever convention we are using, we need to let OptiPath know by setting the feature parameter Later in the Features table.
Later values can be interpreted three different ways: as unknowns, as absences or as zeroes. When choosing a value for Later, the options are Unknown, Absent and Zero.
If the feature parameter Later is set to Unknown, feature values for later artifacts (later than the latest artifact in your data) are assumed to be unknown and the feature will have no effect in the computation of distance between an artifact and those that came after the artifacts in the data set. This means this feature's contribution to the distance, including any transition penalty, is zero.
If the feature parameter Later is set to Absent, feature values for later artifacts are treated like absences and will affect the computation of transition penalties but otherwise they are treated like unknown values and have no effect in computing distance between artifacts.
If the feature parameter Later is set to Zero, feature values for later artifacts will be interpreted according to the setting for the feature parameter Zeroes. You can indicate that later artifacts should be assumed to have both a value of zero and an absence by telling OptiPath to interpret later artifacts as having a value of zero and to interpret zeroes as both a value and an absence (see Zeroes).
Each setting for Later can lead to different results in seriation. For more information see Setting the Earlier, Later, Blanks, Zeroes and Transition Parameters.