In BacktrackKit, a refiner is implemented as a record that must contain:
A member called name, which is a string giving the name of the constraint;
A member called largest_required_point, which is an integer which gives the smallest size partition this refiner will work on. For example, given a set we would expect this to be the largest element of the set.
A member called constraint, which is a constraint object, such that the refiner is refining for the permutations that satisfy the constraint.
A member called refine, which is a record; more information is given below.
A constraint may also optionally contain any of the following members:
A member called btdata. The data in this member will be automatically saved and restored on backtrack.
refineThe refine member of a constraint is a record that contains functions which, if present, will be called to inform the constraint of behaviour as search progresses, and to give the constraint the opportunity to influence the search. The permissible functions are given described below.
These functions will always be passed at least two arguments: firstly the constraint itself, and then the partition stack. Details of any further arguments are described with the relevant function, below.
initialise (required). This is called when search begins. Note that, since the refine.initialise function is called for all relevant constraints at the beginning of search, the partition may have already been split by some earlier constraint by the time that refine.initialise is called for a later constraint.
At most one of the following two functions will generally be implemented.
changed - Will be called after one or more splits in the partition occur.
fixed - Will be called after one or more points in the partition became fixed.
rBaseFinished - The rBase has been created (is passed the rbase). Constraints which care about this can use this to remember the rBase construction is finished.
‣ DummyRefiner( constraint ) | ( attribute ) |
This wraps a constraint in a refiner that doesn't do any refining.
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