The Extent dialog box determines the extent parameters of the search and
is reached from the Strategy menu item.
14.1 Size p_1,..,p_q =
This is formally the size p1,...,pq of the regular
partition, as defined in reference 2. It must be a string of descending integers
separated by spaces or a comma. For example,
2,2,1 for partitions of the form:
A = (XiÇXj)
È(XkÇXl)ÈXm
14.2 Up to p_1 .. p_q
If this is checked, the search will generate all partitions up to and equal to the
size specified in
the previous item. The search procedure is "bottom up", that is,
from lower to higher size. Specifically, the search begins with q = 1, then q = 2 partitions
and so forth. For a given q, the pi also work their way upwards until the specified upper values are attained, while satisfying p1
³ p2
³ ... ³
pq and with
the leftmost value increasing the fastest. For example, generating up to (3,3,3)
generates the following sequence:
(1), (2), (3)
(1,1), (2,1), (3,1), (2,2), (3,2), (3,3)
(1,1,1), (2,1,1), (3,1,1), (2,2,1), (3,2,1), (3,3,1), (2,2,2), (3,2,2) (3,3,2),
(3,3,3)
14.3 A and A-
If the "A and A-" radio button is selected, partitions are generated in a
size for which represenation of both A and A- is generated by the lock and key algorithm.
That is, for a disjunctive normal form (dnf) such
A = (X1ÇX2)È(X3ÇX4)ÈX5
a corresponding dnf for A- is also generated:
A- = (not X1Ç
not X2)È(not X3Ç
not X4)È not
X5
This imposes a certain symmetry on the search and normally you would want to generate both forms; it is the recommended mode. But you can restrict to either
forms if you wish.
It is possible that the same optimal partition will result whether you use
any of these options,
but it is not necessarily the case. With the restrictive
option A or A- only, the search will probably be less extensive.
14.4 Number of float levels
If 1 is entered the cuts of all variables in the search subset are considered fixed
at the optimal level. If 2 is entered, the search allows the optimal and next ranked
optimal cuts (of attributes in the attribute set with more than one specified cut)
in the
search, alternating between the two. If 3 is entered the best 3 cuts are
allowed to float. You cannot allow more than 3 cuts to float. Note that if floating
is requested and there are many cuts for each variable, the sub-searching procedure
may make a search prohibitively large (see Appendix A2.2).
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