School of Population Health

Appendix 6. Skipped partitions

During a search partitions may be skipped to avoid turning the same stone twice (See 15.1). As mentioned in 15.1, no record is kept of all partitions generated so partitions are only skipped on theoretical grounds, that is, when it is presumed that a partition has already been generated or will subsequently be generated. Information on why partitions are skipped is sent to the output log during a search and a summary is written in the Search Extent Box (18.1.1). The following messages may occur:

All are skipped, subset of ...

This message arises if searching up to a given size and if both conjunctive and disjunctive forms are requested in the Search Extent Menu. because less complex partitions in the hierarchy are covered by more complex ones. Specifically, the p₁,...,p_qclass with p₁ > 1 and p_i = 1 for all i = 2,...,q is a subset of the class q,q,...,q, the number of q's being p₁. So that, for example, the class 2,2 covers the class 2,1.

Another skipping message is:

x are skipped because Less than initial specified upto

where x is the number of skipped partitions. This message arises in iterative mode when substitution of the added attribute and Boolean simplification leads to a partition that must have been covered on the initial iteration.

Another skipping message is:

n are skipped because Already covered; no added attribute

This arises in iterative mode if the partition to be generated does not contain the attribute created on the previous iteration. If it does not then there is no point in generating the partition for it must already have been generated on the initial iteration. SPAN calculates the number of such exclusions in advance of the search, by the #( Excl) entry of the Search Extent Box (see18.1.1).

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