Heuristic that uses the results of lookahead. More...
#include <lookahead.h>
Public Member Functions | |
| Literal | doSelect (Solver &s) |
| Implements the actual selection process. | |
| void | endInit (Solver &s) |
| virtual bool | notify (Solver &) |
| UnitHeuristic (const Lookahead::Params &p) | |
| void | updateVar (const Solver &s, Var v, uint32 n) |
Static Public Member Functions | |
| static UnitHeuristic * | restricted (const Lookahead::Params &p, uint32 numOps, DecisionHeuristic *other) |
| Decorates the heuristic given in other with temporary lookahead of type t. | |
Protected Types | |
| typedef SingleOwnerPtr< Lookahead > | LookPtr |
Protected Attributes | |
| LookPtr | look_ |
Detailed Description
Heuristic that uses the results of lookahead.
The heuristic creates and installs a Lookahead post propagator. It then selects the literal with the highest score, where the score is determined by counting assignments made during failed-literal detection. hybrid_lookahead simply selects the literal that derived the most literals. uniform_lookahead behaves similar to the smodels lookahead heuristic (the literal that maximizes the minimum is selected).
- See also:
- Patrik Simons: "Extending and Implementing the Stable Model Semantics" for a detailed description of the lookahead Decision Heuristics.
- Note:
- The heuristic might itself apply some lookahead but only on variables that did not fail in a previous call to Lookahead::propagateFixpoint(). I.e. if priorities are correct for all post propagators in s, the lookahead operations can't fail.
Definition at line 226 of file lookahead.h.
Member Typedef Documentation
typedef SingleOwnerPtr<Lookahead> Clasp::UnitHeuristic::LookPtr [protected] |
Definition at line 239 of file lookahead.h.
Constructor & Destructor Documentation
| Clasp::UnitHeuristic::UnitHeuristic | ( | const Lookahead::Params & | p | ) | [explicit] |
- Parameters:
-
p Lookahead parameters to apply during lookahead.
Definition at line 342 of file lookahead.cpp.
Member Function Documentation
| Literal Clasp::UnitHeuristic::doSelect | ( | Solver & | ) | [virtual] |
Implements the actual selection process.
- Precondition:
- s.numFreeVars() > 0, i.e. there is at least one variable to branch on.
- Returns:
- a literal that is currently free or
- a sentinel literal. In that case, the heuristic shall have asserted a literal!
Implements Clasp::DecisionHeuristic.
Reimplemented in Clasp::Restricted.
Definition at line 353 of file lookahead.cpp.
| void Clasp::UnitHeuristic::endInit | ( | Solver & | ) | [virtual] |
Called once after all problem constraints are known to the solver and the problem was simplified. The default-implementation is a noop.
- Parameters:
-
s The solver in which this heuristic is used.
Reimplemented from Clasp::DecisionHeuristic.
Reimplemented in Clasp::Restricted.
Definition at line 346 of file lookahead.cpp.
| virtual bool Clasp::UnitHeuristic::notify | ( | Solver & | ) | [inline, virtual] |
Reimplemented in Clasp::Restricted.
Definition at line 237 of file lookahead.h.
| UnitHeuristic * Clasp::UnitHeuristic::restricted | ( | const Lookahead::Params & | p, |
| uint32 | numOps, | ||
| DecisionHeuristic * | other | ||
| ) | [static] |
Decorates the heuristic given in other with temporary lookahead of type t.
Definition at line 434 of file lookahead.cpp.
| void Clasp::UnitHeuristic::updateVar | ( | const Solver & | , |
| Var | , | ||
| uint32 | |||
| ) | [virtual] |
Called if the state of one or more variables changed. A state change is one of:
- A previously eliminated variable is resurrected.
- A new aux variable was added.
- An aux variable was removed.
- Parameters:
-
s Solver in which the state change occurred. v The first variable affected by the change. n The range of variables affected, i.e. [v, v+n).
- Note:
- Use s.validVar(v) and s.auxVar(v) to determine the reason for the update.
Implements Clasp::DecisionHeuristic.
Reimplemented in Clasp::Restricted.
Definition at line 376 of file lookahead.cpp.
Member Data Documentation
LookPtr Clasp::UnitHeuristic::look_ [protected] |
Definition at line 240 of file lookahead.h.
The documentation for this class was generated from the following files: