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/******************************************************************************
* Top contributors (to current version):
* Michael Chang, Yancheng Ou
*
* This file is part of the cvc5 project.
*
* Copyright (c) 2009-2021 by the authors listed in the file AUTHORS
* in the top-level source directory and their institutional affiliations.
* All rights reserved. See the file COPYING in the top-level source
* directory for licensing information.
* ****************************************************************************
*
* Optimizer for Integer type.
*/
#include "omt/integer_optimizer.h"
#include "options/smt_options.h"
#include "smt/smt_engine.h"
using namespace cvc5::smt;
namespace cvc5::omt {
OptimizationResult OMTOptimizerInteger::optimize(SmtEngine* optChecker,
TNode target,
bool isMinimize)
{
// linear search for integer goal
// the smt engine to which we send intermediate queries
// for the linear search.
NodeManager* nm = optChecker->getNodeManager();
optChecker->push();
Result intermediateSatResult = optChecker->checkSat();
// Model-value of objective (used in optimization loop)
Node value;
if (intermediateSatResult.isUnknown()
|| intermediateSatResult.isSat() == Result::UNSAT)
{
return OptimizationResult(intermediateSatResult, value);
}
// node storing target > old_value (used in optimization loop)
Node increment;
Kind incrementalOperator = kind::NULL_EXPR;
if (isMinimize)
{
// if objective is minimize,
// then assert optimization_target < current_model_value
incrementalOperator = kind::LT;
}
else
{
// if objective is maximize,
// then assert optimization_target > current_model_value
incrementalOperator = kind::GT;
}
Result lastSatResult = intermediateSatResult;
// Workhorse of linear search:
// This loop will keep incrmenting/decrementing the objective until unsat
// When unsat is hit,
// the optimized value is the model value just before the unsat call
while (intermediateSatResult.isSat() == Result::SAT)
{
lastSatResult = intermediateSatResult;
value = optChecker->getValue(target);
Assert(!value.isNull());
increment = nm->mkNode(incrementalOperator, target, value);
optChecker->assertFormula(increment);
intermediateSatResult = optChecker->checkSat();
}
optChecker->pop();
return OptimizationResult(lastSatResult, value);
}
OptimizationResult OMTOptimizerInteger::minimize(SmtEngine* optChecker,
TNode target)
{
return this->optimize(optChecker, target, true);
}
OptimizationResult OMTOptimizerInteger::maximize(SmtEngine* optChecker,
TNode target)
{
return this->optimize(optChecker, target, false);
}
} // namespace cvc5::omt
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