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deleteffc(?Var, +List, -Rest)
Select from List the variable Var which has the smallest domain and most
constraints and return the rest of the list.
- -Var
- A variable.
- -Rest
- A term unifying with a list of domain variables or integers.
- +List
- A list of domain variables or integers.
Description
This predicate is used in the labeling procedures. When we look for the
instantiation of a list of domain variables which is consistent with a
set of constraints, it is better to start with instantiations which are
most likely to fail, because this will cut down the size of the search
space considerably. The predicate deleteffc/3 selects among the
variables with the smallest domain that one which has most constraints
attached to it. This choice is based on the heuristics that variables
with more constraints are more likely to fail when instantiated.
If several variables are equally eligible, the leftmost one in the
list is taken. Constants are treated like variables of domain size
one with no constraints attached. The list Rest is the same as
List except that the selected element is missing. In particular,
any existing list order is preserved.
Fail Conditions
Fails if List is nil.
Resatisfiable
No.
See Also
constraints_number / 2, deleteff / 3, indomain / 1, fd_search : search / 6