OKlibrary  0.2.1.6
ActiveClauseSets.hpp File Reference

Plans for the concept of an active clause-set. More...

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Detailed Description

Plans for the concept of an active clause-set.

Todo:
The following needs to be updated.
  • See supermodule Satisfiability/ProblemInstances.
  • See supermodule ComputerAlgebra/Satisfiability.
  • This file shall be partially moved to Satisfiability/ProblemInstances/ActiveClauseSets/concepts/plans and partially to Satisfiability/ProblemInstances/ClauseSets/concepts/plans.
Todo:
Dictionary: (The following is out-dated! "clause" -> "active clause" and "clause-set" -> "active clause-set")
  1. "clause" generalised to "constraint" enhanced to "active clause-set" (semantically like a constraint, but can be viewed as a clause-set)
  2. "clause-set" generalised to "constraint satisfaction problem" enhanced to "alliance of active clause-sets".

Ordinary clause-sets however should now be treated as active clause-sets, and not as alliances of active clause-sets, since alliances of active clause-sets assume that there constituents are intelligent but not numerous.

Todo:
Update with Concepts/plans/ClauseSets.hpp (transferring ideas from there to here or the other way around (?!)).
Todo:
Partial assignment (see Concepts/plans/PartialAssignments.hpp)
  • An active clause-set (ACLS F in the sequel) has a connection to the main partial assignment:
    • it can process the new assignments
    • and it can undo them.
  • The concept of partial assignments needs to support this. Actually, speaking of "partial assignments" might be a bit misleading, since literals for us are kind of arbitrary constraints ?!
  • A problem here is, that we might have different types of literals (for example unary and binary literals), and because of static typing then we need actually a tuple of partial assignments, collected into the "super-assignment" phi.
Todo:
Evaluation
  • The current partial assignment phi can be evaluated (written phi(F)), returning a 4-valued object:
    • 0 if all total assignments extending phi falsify F
    • 1 if all total assignments extending phi satisify F
    • 0/1 if there are total assignments extending phi falsifing and satisfying F
    • unknown (can not be returned if all variables of F got a unique value).
  • So we need to extend Boost::tribool by a "4-valued logic"; we need literature on that (see verification of circuits).
Todo:
Implied literals
  • The literal type of F is the same as for the associated partial assignment.
  • Processing the new assignment creates a list of implied literals (or should this be a partial assignment?).
  • If there are for example literals for equality, then this included implied equivalences.
Todo:
Support for local search
  • Given a total assignment for the variables, an alteration is produced which satisfies F or comes as close as possible to that. (Total assignment means that all variables are fixed; perhaps here we should consider only unary literals?)
  • For autarky search, here it must also be possible to disable variables; this is easiest understand by referring to an underlying clause-model.
Todo:
Causes of conflict
  • For partial assignments, let "phi' <= phi" be true if var(phi') <= var(phi) and for all in var(phi') the literals phi'(v) weakens phi(v) (the set of allowed values of phi'(v) contains the set of allowed values of phi(v)).
  • Now if phi(F) = 0, then phi' is computed with phi' <= phi and phi'(F) = 0.
Todo:
Autarkies: What is an appropriate notions of autarkies? Easiest is to refer to some underlying clause-model ?!
Todo:
For a "strong ACLS" all above operations are poly-time in the number of variables, and are always complete (no "unknow" for evaluation, all implied literals and equivalences, the changed total assignment is satisfying). XXX This should be now "active clauses".
Todo:
Should we have statistics for an underlying clause-model? XXX This seems to be the point of speaking of "active clause-sets".
Todo:
CNF versus DNF
  • Regarding QBF for example, we should allow to represent conditions as CNFs and as DNFs (that is, as sets of (partial) falsifying assignments resp. (partial) satisfying assignments), potentially also allowing mixed representations.
  • One could also regard partial representations, that is, the condition itself recognises the satisfying and the falsying total assignments, but it might have only some partial CNF- or DNF-clauses "in it" (those found until now).

Definition in file ActiveClauseSets.hpp.