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/****************************************************************************** |
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* Top contributors (to current version): |
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* Andrew Reynolds, Mathias Preiner |
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* |
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* This file is part of the cvc5 project. |
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* |
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* Copyright (c) 2009-2021 by the authors listed in the file AUTHORS |
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* in the top-level source directory and their institutional affiliations. |
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* All rights reserved. See the file COPYING in the top-level source |
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* directory for licensing information. |
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* **************************************************************************** |
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* |
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* Base classes for decision strategies used by theory solvers |
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* for use in the DecisionManager of TheoryEngine. |
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*/ |
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#include "cvc5_private.h" |
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#ifndef CVC5__THEORY__DECISION_STRATEGY__H |
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#define CVC5__THEORY__DECISION_STRATEGY__H |
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#include "context/cdo.h" |
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#include "expr/node.h" |
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#include "smt/env_obj.h" |
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#include "theory/valuation.h" |
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namespace cvc5 { |
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namespace theory { |
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/** |
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* Virtual base class for decision strategies. |
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*/ |
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class DecisionStrategy : protected EnvObj |
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{ |
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public: |
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DecisionStrategy(Env& env) : EnvObj(env) {} |
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virtual ~DecisionStrategy() {} |
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/** |
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* Initalize this strategy, This is called once per satisfiability call by |
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* the DecisionManager, prior to using this strategy. |
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*/ |
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virtual void initialize() = 0; |
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/** |
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* If this method returns a non-null node n, then n is the required next |
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* decision of this strategy. It must be the case that n is a literal in |
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* the current CNF stream. |
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*/ |
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virtual Node getNextDecisionRequest() = 0; |
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/** identify this strategy (for debugging) */ |
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virtual std::string identify() const = 0; |
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}; |
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/** |
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* Decision strategy finite model finding. |
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* |
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* This is a virtual base class for decision strategies that follow the |
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* "finite model finding" pattern for decisions. Such strategies have the |
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* distinguishing feature that they are interested in a stream of literals |
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* L_1, L_2, L_3, ... and so on. At any given time, they request that L_i is |
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* asserted true for a minimal i. |
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* |
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* To enforce this strategy, this class maintains a SAT-context dependent |
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* index d_curr_literal, which corresponds to the minimal index of a literal |
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* in the above list that is not asserted false. A call to |
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* getNextDecisionRequest increments this value until we find a literal L_j |
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* that is not assigned false. If L_j is unassigned, we return it as a decision, |
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* otherwise we return no decisions. |
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*/ |
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class DecisionStrategyFmf : public DecisionStrategy |
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{ |
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public: |
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DecisionStrategyFmf(Env& env, Valuation valuation); |
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virtual ~DecisionStrategyFmf() {} |
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/** initialize */ |
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void initialize() override; |
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/** get next decision request */ |
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Node getNextDecisionRequest() override; |
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/** Make the n^th literal of this strategy */ |
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virtual Node mkLiteral(unsigned n) = 0; |
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/** |
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* This method returns true iff there exists a (minimal) i such that L_i |
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* is a literal allocated by this class, and is asserted true in the current |
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* context. If it returns true, the argument i is set to this i. |
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*/ |
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bool getAssertedLiteralIndex(unsigned& i) const; |
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/** |
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* This method returns the literal L_i allocated by this class that |
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* has been asserted true in the current context and is such that i is |
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* minimal. It returns null if no such literals exist. |
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*/ |
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Node getAssertedLiteral(); |
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/** Get the n^th literal of this strategy */ |
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Node getLiteral(unsigned lit); |
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protected: |
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/** |
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* The valuation of this class, used for knowing what literals are asserted, |
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* and with what polarity. |
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*/ |
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Valuation d_valuation; |
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/** |
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* The (SAT-context-dependent) flag that is true if there exists a literal |
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* of this class that is asserted true in the current context, according to |
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* d_valuation. |
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*/ |
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context::CDO<bool> d_has_curr_literal; |
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/** |
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* The (SAT-context-dependent) index of the current literal of this strategy. |
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* This corresponds to the first literal that is not asserted false in the |
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* current context, according to d_valuation. |
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*/ |
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context::CDO<unsigned> d_curr_literal; |
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/** the list of literals of this strategy */ |
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std::vector<Node> d_literals; |
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}; |
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/** |
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* Special case of above where we only wish to allocate a single literal L_1. |
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*/ |
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class DecisionStrategySingleton : public DecisionStrategyFmf |
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{ |
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public: |
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DecisionStrategySingleton(Env& env, |
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const char* name, |
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Node lit, |
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Valuation valuation); |
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/** |
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* Make the n^th literal of this strategy. This method returns d_literal if |
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* n=0, null otherwise. |
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*/ |
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Node mkLiteral(unsigned n) override; |
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/** Get single literal */ |
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Node getSingleLiteral(); |
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/** identify */ |
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std::string identify() const override { return d_name; } |
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private: |
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/** the name of this strategy */ |
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std::string d_name; |
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/** the literal to decide on */ |
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Node d_literal; |
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}; |
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} // namespace theory |
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} // namespace cvc5 |
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#endif /* CVC5__THEORY__DECISION_STRATEGY__H */ |