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/********************* */
/*! \file symmetry_breaker.cpp
** \verbatim
** Top contributors (to current version):
** Paul Meng, Andrew Reynolds
** This file is part of the CVC4 project.
** Copyright (c) 2009-2018 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.\endverbatim
**
** \brief Symmetry breaker module
**/
#include "preprocessing/passes/symmetry_breaker.h"
#include "preprocessing/passes/symmetry_detect.h"
using namespace std;
using namespace CVC4::kind;
namespace CVC4 {
namespace preprocessing {
namespace passes {
Node SymmetryBreaker::generateSymBkConstraints(const vector<vector<Node>>& parts)
{
vector<Node> constraints;
NodeManager* nm = NodeManager::currentNM();
for (const vector<Node>& part : parts)
{
if (part.size() >= 2)
{
Kind kd = getOrderKind(part[0]);
if (kd == UNDEFINED_KIND)
{
// no symmetry breaking possible
continue;
}
if (kd != EQUAL)
{
for (unsigned int i = 0; i < part.size() - 1; ++i)
{
// Generate less than or equal to constraints: part[i] <= part[i+1]
Node constraint = nm->mkNode(kd, part[i], part[i + 1]);
constraints.push_back(constraint);
Trace("sym-bk")
<< "[sym-bk] Generate a symmetry breaking constraint: "
<< constraint << endl;
}
}
else if (part.size() >= 3)
{
for (unsigned int i = 0; i < part.size(); ++i)
{
for (unsigned int j = i + 2; j < part.size(); ++j)
{
// Generate consecutive constraints v_i = v_j => v_i = v_{j-1},
// for all 0 <= i < j-1 < j < part.size()
Node constraint = nm->mkNode(IMPLIES,
nm->mkNode(kd, part[i], part[j]),
nm->mkNode(kd, part[i], part[j - 1]));
constraints.push_back(constraint);
Trace("sym-bk")
<< "[sym-bk] Generate a symmetry breaking constraint: "
<< constraint << endl;
}
if (i >= 1)
{
for (unsigned int j = i + 1; j < part.size(); ++j)
{
Node lhs = nm->mkNode(kd, part[i], part[j]);
Node rhs = nm->mkNode(kd, part[i], part[i - 1]);
int prev_seg_start_index = 2*i - j - 1;
// Since prev_seg_len is always less than i - 1, we just need to make
// sure prev_seg_len is greater than or equal to 0
if(prev_seg_start_index >= 0)
{
rhs = nm->mkNode(
OR,
rhs,
nm->mkNode(kd, part[i - 1], part[prev_seg_start_index]));
}
// Generate length order constraints
// v_i = v_j => (v_{i} = v_{i-1} OR v_{i-1} = x_{(i-1)-(j-i)})
// for all 1 <= i < j < part.size() and (i-1)-(j-i) >= 0
Node constraint = nm->mkNode(IMPLIES, lhs, rhs);
constraints.push_back(constraint);
Trace("sym-bk")
<< "[sym-bk] Generate a symmetry breaking constraint: "
<< constraint << endl;
}
}
}
}
}
}
if(constraints.empty())
{
return d_trueNode;
}
else if(constraints.size() == 1)
{
return constraints[0];
}
return nm->mkNode(AND, constraints);
}
Kind SymmetryBreaker::getOrderKind(Node node)
{
TypeNode tn = node.getType();
if (tn.isBoolean())
{
return IMPLIES;
}
else if (tn.isReal())
{
return LEQ;
}
else if (tn.isBitVector())
{
return BITVECTOR_ULE;
}
if (tn.isFirstClass())
{
return EQUAL;
}
return UNDEFINED_KIND;
}
SymBreakerPass::SymBreakerPass(PreprocessingPassContext* preprocContext)
: PreprocessingPass(preprocContext, "sym-break"){};
PreprocessingPassResult SymBreakerPass::applyInternal(
AssertionPipeline* assertionsToPreprocess)
{
Trace("sym-break-pass") << "Apply symmetry breaker pass..." << std::endl;
// detect symmetries
std::vector<std::vector<Node>> sterms;
symbreak::SymmetryDetect symd;
symd.computeTerms(sterms, assertionsToPreprocess->ref());
if (Trace.isOn("sym-break-pass") || Trace.isOn("sb-constraint"))
{
if (sterms.empty())
{
Trace("sym-break-pass") << "Detected no symmetric terms." << std::endl;
}
else
{
Trace("sb-constraint") << "; found symmetry" << std::endl;
Trace("sym-break-pass") << "Detected symmetric terms:" << std::endl;
for (const std::vector<Node>& p : sterms)
{
Trace("sym-break-pass") << " " << p << std::endl;
}
}
}
// construct the symmetry breaking constraint
Trace("sym-break-pass") << "Construct symmetry breaking constraint..."
<< std::endl;
SymmetryBreaker symb;
Node sbConstraint = symb.generateSymBkConstraints(sterms);
// add symmetry breaking constraint to the set of assertions
Trace("sym-break-pass") << "...got: " << sbConstraint << std::endl;
// if not true
if (!sbConstraint.isConst())
{
Trace("sb-constraint") << "(symmetry-break " << sbConstraint << ")"
<< std::endl;
// add to assertions
assertionsToPreprocess->push_back(sbConstraint);
}
return PreprocessingPassResult::NO_CONFLICT;
}
} // namespace passes
} // namespace preprocessing
} // namespace CVC4
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