-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
* Renamed InvariantCheck heuristic to GoalInvariantCheck, for clarity * Some tweaks to (Goal)InvariantCheck * Re-enabled BackStateSpaceSearchTests
- Loading branch information
Showing
4 changed files
with
126 additions
and
79 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
93 changes: 93 additions & 0 deletions
93
src/SCClassicalPlanning/Planning/StateSpaceSearch/Heuristics/GoalInvariantCheck.cs
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,93 @@ | ||
| using SCClassicalPlanning.ProblemManipulation; | ||
| using SCFirstOrderLogic; | ||
| using SCFirstOrderLogic.Inference; | ||
| using SCFirstOrderLogic.SentenceManipulation; | ||
|
|
||
| namespace SCClassicalPlanning.Planning.StateSpaceSearch.Heuristics | ||
| { | ||
| /// <summary> | ||
| /// A decorator heuristic that checks whether the goal violates any known invariants | ||
| /// before invoking the inner heuristic. If any invariants are violated, returns <see cref="float.PositiveInfinity"/>. | ||
| /// Intended to be of use for early pruning of unreachable goals when backward searching. | ||
| /// <para/> | ||
| /// NB #1: This heuristic isn't driven by any particular source material, but given that it's a fairly | ||
| /// obvious idea, there could well be some terminology that I'm not using - I may rename/refactor it as and when. | ||
| /// <para/> | ||
| /// NB #2: Checking invariants obviously comes at a performance cost (though fact that goals consist only of unit | ||
| /// clauses likely mitigates this quite a lot - because it means that the negation of the query we ask our KB it | ||
| /// consists only of unit clauses). | ||
| /// The question is whether the benefit it provides outweighs the cost. I do wonder if we can somehow check | ||
| /// only the stuff that has changed. | ||
| /// <para/> | ||
| /// NB #3: Ultimately it should be possible to derive the invariants by examining the problem. | ||
| /// The simplest example of this is if a predicate doesn't appear in any effects. If this is true, the | ||
| /// the occurences of this predicate in the initial state must persist throughout the problem. | ||
| /// Might research / play with this idea at some point. | ||
| /// </summary> | ||
| public class GoalInvariantCheck | ||
| { | ||
| private readonly Func<State, Goal, float> innerHeuristic; | ||
| private readonly IKnowledgeBase knowledgeBase; | ||
|
|
||
| /// <summary> | ||
| /// Initializes a new instance of the <see cref="GoalInvariantCheck"/>. | ||
| /// </summary> | ||
| /// <param name="invariantsKnowledgeBase">A knowledge base containing all of the invariants of the problem.</param> | ||
| /// <param name="innerHeuristic">The inner heuristic to invoke if no invariants are violated by the goal.</param> | ||
| public GoalInvariantCheck(IKnowledgeBase invariantsKnowledgeBase, Func<State, Goal, float> innerHeuristic) | ||
| { | ||
| this.innerHeuristic = innerHeuristic; | ||
| this.knowledgeBase = invariantsKnowledgeBase; | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// Estimates the cost of getting from the given state to a state that satisfies the given goal. | ||
| /// </summary> | ||
| /// <param name="state">The state.</param> | ||
| /// <param name="goal">The goal.</param> | ||
| /// <returns><see cref="float.PositiveInfinity"/> if any invariants are violated by the goal. Otherwise, the cost estimated by the inner heuristic.</returns> | ||
| public float EstimateCost(State state, Goal goal) | ||
| { | ||
| // One would assume that the inner heuristic would return 0 if there are no elements | ||
| // in the goal - but its not our business to shortcut that | ||
| if (goal.Elements.Count > 0) | ||
| { | ||
| var variables = new HashSet<VariableDeclaration>(); | ||
| GoalVariableFinder.Instance.Visit(goal, variables); | ||
|
|
||
| // Annoying performance hit - goals are essentially already in CNF, but our knowledge bases want to do the conversion themselves.. Meh, never mind. | ||
| // TODO: Perhaps a ToSentence in Goal? (and others..) | ||
| var goalSentence = goal.Elements.Skip(1).Aggregate(goal.Elements.First().ToSentence(), (c, e) => new Conjunction(c, e.ToSentence())); | ||
|
|
||
| foreach (var variable in variables) | ||
| { | ||
| goalSentence = new ExistentialQuantification(variable, goalSentence); | ||
| } | ||
|
|
||
| // Note the negation here. We're not asking if the invariants mean that the goal MUST | ||
| // be true (that will of course generally not be the case!), we're asking if the goal | ||
| // CANNOT be true - that is, if its NEGATION must be true. | ||
| if (knowledgeBase.Ask(new Negation(goalSentence))) | ||
| { | ||
| return float.PositiveInfinity; | ||
| } | ||
| } | ||
|
|
||
| return innerHeuristic(state, goal); | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// Utility class to find <see cref="Constant"/> instances within the elements of a <see cref="SCClassicalPlanning.Goal"/>, and add them to a given <see cref="HashSet{T}"/>. | ||
| /// </summary> | ||
| private class GoalVariableFinder : RecursiveGoalVisitor<HashSet<VariableDeclaration>> | ||
| { | ||
| /// <summary> | ||
| /// Gets a singleton instance of the <see cref="GoalVariableFinder"/> class. | ||
| /// </summary> | ||
| public static GoalVariableFinder Instance { get; } = new(); | ||
|
|
||
| /// <inheritdoc/> | ||
| public override void Visit(VariableDeclaration variable, HashSet<VariableDeclaration> variables) => variables.Add(variable); | ||
| } | ||
| } | ||
| } |
67 changes: 0 additions & 67 deletions
67
src/SCClassicalPlanning/Planning/StateSpaceSearch/Heuristics/InvariantCheck.cs
This file was deleted.
Oops, something went wrong.