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/**
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2018, IMT Atlantique. All rights reserved.
*
* Licensed under the BSD 4-clause license.
*
* See LICENSE file in the project root for full license information.
*/
package org.chocosolver.sat;
import gnu.trove.list.TIntList;
import gnu.trove.list.array.TIntArrayList;
import gnu.trove.map.hash.TIntObjectHashMap;
import gnu.trove.map.hash.TLongIntHashMap;
import org.chocosolver.memory.IStateInt;
import org.chocosolver.sat.SatSolver.Clause;
import org.chocosolver.solver.Model;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.BoolVar;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.Variable;
import org.chocosolver.util.ESat;
import java.util.*;
import static org.chocosolver.sat.SatSolver.*;
/**
* A propagator to store and propagate no-goods.
*
* Created by cprudhom on 20/01/15.
* Project: choco.
* @author Charles Prud'homme
*/
public class PropNogoods extends Propagator {
/**
* No entry value for {@link #lit2val}, {@link #lit2pos} and {@link #var2pos}.
*/
private static final int NO_ENTRY = Integer.MAX_VALUE;
/**
* Mask to signed value.
* The 33^th bit is set to 0 for "= value" and to 1 for "<= value".
*/
private static final long BITOP = 1L << 33L;
/**
* Frontier between "= value" (below) and "<= value" (above)
*/
private static final long FRONTIER = BITOP - Integer.MAX_VALUE;
/**
* The underlying SAT solver
*/
private SatSolver sat_;
/**
* Binds couple (variable-value) to a unique literal
*/
private TLongIntHashMap[] vv2lit;
/**
* Binds variable ({@link Variable#getId()} to a unique position
*/
private int[] var2pos;
/**
* Binds literal to variable
*/
private int[] lit2pos;
/**
* Binds literal to value.
* A value is typically a signed int.
* The 32^th bit is set to 0 for "= value" and to 1 for "<= value".
*/
private long[] lit2val;
/**
* For comparison with SAT solver trail, to deal properly with backtrack
*/
private IStateInt sat_trail_;
/**
* List of early deduction literals
*/
private TIntList early_deductions_;
/**
* Local-like parameter.
* To reduce learnt no-goods.
*/
private BitSet test_eq;
/**
* Since there is no domain-clause, a fix point may not be reached by SatSolver itself.
* Stores all modified variable to make sure a fix point is reached.
*/
private Deque fp;
/**
* Local-like parameter, for #why() method only, lazily initialized.
*/
private TIntObjectHashMap> inClauses;
/**
* Store new added variables when {@link #initialized} is false
*/
private ArrayList add_var;
/**
* Indicates if this is initialized or not
*/
private boolean initialized = false;
/**
* Create a (unique) propagator for no-goods recording and propagation.
*
* @param model the model that declares the propagator
*/
public PropNogoods(Model model) {
super(new BoolVar[]{model.boolVar(true)}, PropagatorPriority.VERY_SLOW, true);
this.vars = new IntVar[0];// erase model.ONE from the variable scope
int k = 16;
this.vv2lit = new TLongIntHashMap[k];//new TIntObjectHashMap<>(16, .5f, NO_ENTRY);
this.lit2val = new long[k];//new TIntIntHashMap(16, .5f, NO_ENTRY, NO_ENTRY);
Arrays.fill(lit2val, NO_ENTRY);
this.lit2pos = new int[k];//new TIntIntHashMap(16, .5f, NO_ENTRY, NO_ENTRY);
Arrays.fill(lit2pos, NO_ENTRY);
this.var2pos = new int[k];//new TIntIntHashMap(16, .5f, NO_ENTRY, NO_ENTRY);
Arrays.fill(var2pos, NO_ENTRY);
//TODO: one satsolver per model...
sat_ = new SatSolver();
early_deductions_ = new TIntArrayList();
sat_trail_ = model.getEnvironment().makeInt();
test_eq = new BitSet();
fp = new ArrayDeque<>();
add_var = new ArrayList<>(16);
}
@Override
public void propagate(int evtmask) throws ContradictionException {
initialize();
if (!sat_.ok_) fails();
fp.clear();
sat_.cancelUntil(0); // to deal with learnt clauses, only called on coarse grain propagation
storeEarlyDeductions();
applyEarlyDeductions();
for (int i = 0; i < vars.length; ++i) {
doVariableBound(vars[i]);
}
while (fp.size() > 0) {
doVariableBound(fp.pollFirst());
}
}
@Override
public void propagate(int idxVarInProp, int mask) throws ContradictionException {
fp.clear();
doVariableBound(vars[idxVarInProp]);
while (fp.size() > 0) {
doVariableBound(fp.pollFirst());
}
}
private void doVariableBound(IntVar var) throws ContradictionException {
TLongIntHashMap map;
for (long k : (map = vv2lit[var.getId()]).keys()) {
int value = ivalue(k);
if (iseq(k)) {
if (var.contains(value)) {
if (var.isInstantiated()) {
VariableBound(map.get(k), true);
}
} else {
VariableBound(map.get(k), false);
}
} else {
if (var.getUB() <= value) {
VariableBound(map.get(k), true);
} else if (var.getLB() > value) {
VariableBound(map.get(k), false);
}
}
}
}
@Override
public ESat isEntailed() {
if (vars.length == 0) return ESat.TRUE;
if (isCompletelyInstantiated()) {
boolean OK = true;
int var, val;
long value;
boolean sign, eq;
for (int k : sat_.implies_.keys()) {
sign = sign(negated(k));
var = var(k);
IntVar ivar = vars[lit2pos[var]];
value = lit2val[var];
eq = iseq(value);
val = ivalue(value);
if ((eq && sign != ivar.contains(val))
|| (!eq && sign != ivar.getUB() <= val)) {
OK &= impliesEntailed(sat_.implies_.get(k));
}
}
OK &= clauseEntailed(sat_.clauses);
OK &= clauseEntailed(sat_.learnts);
return ESat.eval(OK);
}
return ESat.UNDEFINED;
}
private boolean impliesEntailed(TIntList lits) {
int var;
long value;
boolean sign;
IntVar ivar;
for (int l : lits.toArray()) {
sign = sign(l);
var = var(l);
ivar = vars[lit2pos[var]];
value = lit2val[var];
if (iseq(value)) {
if (sign != ivar.contains(ivalue(value))) {
return false;
}
} else {
if (sign && ivar.getLB() > ivalue(value)) {
return false;
} else if (!sign && ivar.getUB() <= ivalue(value)) {
return false;
}
}
}
return true;
}
private boolean clauseEntailed(ArrayList clauses) {
int lit, var;
long value;
boolean sign;
IntVar ivar;
for (Clause c : clauses) {
int cnt = 0;
for (int i = 0; i < c.size(); i++) {
lit = c._g(i);
sign = sign(lit);
var = var(lit);
ivar = vars[lit2pos[var]];
value = lit2val[var];
if (iseq(value)) {
if (sign != ivar.contains(ivalue(value))) {
cnt++;
} else break;
} else {
if (sign && ivar.getLB() > ivalue(value)) {
cnt++;
} else if (!sign && ivar.getUB() <= ivalue(value)) {
cnt++;
} else break;
}
}
if (cnt == c.size()) return false;
}
return true;
}
/**
* @param v a value
* @return true if the value encodes '=', false if it encodes '≤'.
*/
static boolean iseq(long v) {
return v < FRONTIER;
}
/**
* @param v a value
* @return v with `≤' information encoded into it
*/
static long leq(int v) {
return v + BITOP;
}
/**
* @param v a value
* @return the value without the '=' or '≤' information.
*/
static int ivalue(long v) {
return (int)(iseq(v)?v:v - BITOP);
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
* Initializes this propagator
*/
public void initialize() {
if (!initialized) {
if (add_var.size() > 0) {
addVariable(add_var.toArray(new IntVar[0]));
}
add_var.clear();
this.initialized = true;
}
}
/**
* Creates or returns if already existing, the literal corresponding to :
*
* ivar (eq?"=":"<=") value
*
* where "=" is selected if eq is true, "<=" otherwise.
*
* The negation of the literal is managed outside.
*
* @param ivar an integer variable
* @param value a value
* @param eq set to true to select "=", to false to select "<=".
* @return the literal corresponding to ivar (eq?"=":"<=") value
*/
public int Literal(IntVar ivar, int value, boolean eq) {
// TODO: deal with BoolVar
int vid = ivar.getId();
int var;
TLongIntHashMap map;
if (vid >= vv2lit.length) {
TLongIntHashMap[] tmp = vv2lit;
vv2lit = new TLongIntHashMap[vid + 1];
System.arraycopy(tmp, 0, vv2lit, 0, tmp.length);
int[] tmpi = var2pos;
var2pos = new int[vid + 1];
System.arraycopy(tmpi, 0, var2pos, 0, tmpi.length);
Arrays.fill(var2pos, tmpi.length, vid + 1, NO_ENTRY);
}
if ((map = vv2lit[vid]) == null) {
map = new TLongIntHashMap(16, .5f, NO_ENTRY, NO_ENTRY);
vv2lit[vid] = map;
}
int pos;
if ((pos = var2pos[vid]) == NO_ENTRY) {
if(initialized) {
addVariable(ivar);
pos = vars.length - 1;
}else {
add_var.add(ivar);
pos = add_var.size() - 1;
}
var2pos[vid] = pos;
}
long lvalue = eq ? value : leq(value);
if ((var = map.get(lvalue)) == NO_ENTRY) {
var = sat_.newVariable();
map.put(lvalue, var);
if (var >= lit2pos.length) {
int[] itmp = lit2pos;
lit2pos = new int[var + 1];
System.arraycopy(itmp, 0, lit2pos, 0, itmp.length);
Arrays.fill(lit2pos, itmp.length, var + 1, NO_ENTRY);
long[] ltmp = lit2val;
lit2val = new long[var + 1];
System.arraycopy(ltmp, 0, lit2val, 0, ltmp.length);
Arrays.fill(lit2val, ltmp.length, var + 1, NO_ENTRY);
}
lit2pos[var] = pos;
lit2val[var] = lvalue;
}
return makeLiteral(var, true);
}
/**
* var points a clause variable whom value is now to be val.
*
* @param index a clause var
* @param sign the sign of the lit
* @throws ContradictionException if inconsistency is detected
*/
void VariableBound(int index, boolean sign) throws ContradictionException {
try {
if (sat_trail_.get() < sat_.trailMarker()) {
sat_.cancelUntil(sat_trail_.get());
assert (sat_trail_.get() == sat_.trailMarker());
}
int lit = makeLiteral(index, sign);
if (!sat_.propagateOneLiteral(lit)) {
// force failure by removing the last value: flip the sign
// explanations require doing the failure
doReduce(negated(lit));
} else {
sat_trail_.set(sat_.trailMarker());
for (int i = 0; i < sat_.touched_variables_.size(); ++i) {
lit = sat_.touched_variables_.get(i);
doReduce(lit);
}
}
} finally {
sat_.touched_variables_.resetQuick(); // issue#327
}
}
/**
* Reduce the variable.
*
* @param lit literal to assign
* @throws ContradictionException if reduction leads to failure
*/
void doReduce(int lit) throws ContradictionException {
int var = var(lit);
long value = lit2val[var];
IntVar ivar = vars[lit2pos[var]];
if (iseq(value)) {
if (sign(lit)) {
ivar.instantiateTo(ivalue(value), this);
} else {
if (ivar.removeValue(ivalue(value), this)) {
fp.push(ivar);
}
}
} else {
if (sign(lit)) {
if (ivar.updateUpperBound(ivalue(value), this)) {
fp.push(ivar);
}
} else if (ivar.updateLowerBound(ivalue(value) + 1, this)) {
fp.push(ivar);
}
}
}
/**
* Add clauses to ensure domain consistency, that is:
*
* -
* [ x ≤ d ] ⇒ [ x ≤ d +1 ]
*
* -
* [ x = d ] ⇔ ([ x ≤ d ] ∧ ¬[ x ≤ d + 1])
*
*
* @param var an integer variable
* @return if clauses have been successfully added to the store.
*/
boolean declareDomainNogood(IntVar var) {
int size = var.getDomainSize();
int[] lits = new int[size * 2];
// 1. generate lits
int a = var.getLB();
int ub = var.getUB();
int i = 0;
while (a <= ub) {
lits[i] = Literal(var, a, true);
lits[i + size] = Literal(var, a, false);
i++;
a = var.nextValue(a);
}
TIntList clauses = new TIntArrayList();
boolean add = false;
// 2. add clauses
// 2a. [ x <= d ] => [ x <= d +1 ]
for (int j = size; j < 2 * size - 1; j++) {
clauses.add(negated(lits[j]));
clauses.add(lits[j + 1]);
add |= sat_.addClause(clauses);
clauses.clear();
}
// 2b. [ x = d ] <=> [ x <= d ] and not[ x <= d +1 ]
for (int k = 0; k < size - 1; k++) {
// [ x = d ] or not[ x <= d ] or [ x <= d +1 ]
clauses.add(lits[k]);
clauses.add(negated(lits[size + k]));
clauses.add(lits[size + k + 1]);
add |= sat_.addClause(clauses);
clauses.clear();
// not [ x = d ] or [ x <= d ]
clauses.add(negated(lits[k]));
clauses.add(lits[size + k]);
add |= sat_.addClause(clauses);
clauses.clear();
// not [ x = d ] or not[ x <= d +1 ]
clauses.add(negated(lits[k]));
clauses.add(negated(lits[size + k + 1]));
add |= sat_.addClause(clauses);
clauses.clear();
}
storeEarlyDeductions();
return add;
}
/**
* Add unit clause to no-goods store
*
* @param p unit clause
* @return false if failure is detected
*/
@SuppressWarnings("unused")
public boolean addNogood(int p) {
boolean result = sat_.addClause(p);
storeEarlyDeductions();
return result;
}
/**
* Add unit clause to no-goods store
*
* @param lits clause
* @return false if failure is detected
*/
@SuppressWarnings("unused")
public boolean addNogood(TIntList lits) {
boolean result = sat_.addClause(lits);
storeEarlyDeductions();
return result;
}
/**
* Add learnt clause to no-goods store
*
* @param lits clause
*/
public void addLearnt(int... lits) {
sat_.learnClause(lits);
// early deductions of learnt clause may lead to incorrect behavior on backtrack
// since early deduction is not backtrackable.
forcePropagationOnBacktrack(); // issue#327
// compare the current clauses with the previous stored one,
// just in case the current one dominates the previous none
if (sat_.nLearnt() > 1) {
Clause last = sat_.learnts.get(sat_.learnts.size() - 1);
test_eq.clear();
for (int i = last.size() - 1; i >= 0; i--) {
test_eq.set(last._g(i));
}
for (int c = sat_.learnts.size() - 2; c >= 0; c--) {
int s = test_eq.cardinality();
Clause prev = sat_.learnts.get(c);
if (last.size() > 1 && last.size() < prev.size()) {
for (int i = prev.size() - 1; i >= 0; i--) {
s -= test_eq.get(prev._g(i)) ? 1 : 0;
}
if (s == 0) { // then last dominates prev
sat_.detachLearnt(c);
}
}
}
}
}
private void storeEarlyDeductions() {
for (int i = 0; i < sat_.touched_variables_.size(); ++i) {
int lit = sat_.touched_variables_.get(i);
early_deductions_.add(lit);
}
sat_.touched_variables_.resetQuick();
}
/**
* Apply early deduction
*
* @throws ContradictionException if it fails
*/
private void applyEarlyDeductions() throws ContradictionException {
for (int i = 0; i < early_deductions_.size(); ++i) {
int lit = early_deductions_.get(i);
doReduce(lit);
}
}
}