org.chocosolver.solver.learn.LazyImplications Maven / Gradle / Ivy
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2022, 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.solver.learn;
import org.chocosolver.memory.IStateInt;
import org.chocosolver.solver.Cause;
import org.chocosolver.solver.ICause;
import org.chocosolver.solver.Model;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.objects.ValueSortedMap;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableRangeSet;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableSetUtils;
import java.util.Comparator;
import java.util.HashMap;
/**
* This implication graph is lazily built.
* It maintains the list of events invoked during propagation on each variable,
* and maintains a copy of each domain.
*
* Data is stored in a stack, where each entry is a tuple:
*
< v, D, c, m, p, n>
* where :
*
* - v is the variable modified,
* - D is its current domain,
* - c is the cause (most of the time, a propagator),
* - m is the mask of event that triggers the modification,
* - p is a pointer to the previous entry on v in the stack
* - n is a pointer to the next entry on v in the stack (if any)
*
*
* Note that, under some conditions, two entries can be merged into a single one.
*
* Project: choco-solver.
* @author Charles Prud'homme
* @since 25/01/2017.
*/
public class LazyImplications extends Implications {
/**
* An entry < v, D, c, m, p, n> where :
*
* - v is the variable modified,
* - D is its current domain,
* - c is the cause (most of the time, a propagator),
* - m is the mask event that triggers the modification,
* - i is the index of this entry in the stack
* - p is a pointer to the previous entry on v in the stack
*
*
* Invar: (p < n) xor ("root entry")
*/
static class Entry implements Comparator {
// modified variable
IntVar v;
// domain after modification
IntIterableRangeSet d;
// who causes the modification
ICause c;
// mask of the event
int m;
int e;
// index of this in the stack
int i;
// index of direct predecessor (same variable)
int p;
// decision level
int dl;
@Override
public String toString() {
return String.format("<%s, %s, %s, %s, %d, %d, %d>", v.getName(), d, c, m, i, p, dl);
}
Entry() {
d = new IntIterableRangeSet();
}
public void set(IntVar v, ICause c, int m, int e, int i, int p, int dl) {
this.v = v;
this.c = c;
this.m = m;
this.e = e;
this.i = i;
this.p = p;
this.dl = dl;
}
public IntIterableRangeSet getD() {
return d;
}
void setPrev(int p) {
this.p = p;
}
@Override
public int compare(Entry o1, Entry o2) {
return o1.i - o2.i;
}
}
/**
* Ordered list of entries.
*/
Entry[] entries;
/**
* Pointer, per variable, to the root entry {@link #entries}
*/
final HashMap rootEntries;
/**
* Number of entries stored -- backtrackable
*/
private final IStateInt size;
/**
* Number of active entries in {@link #entries}
*/
private int nbEntries;
/**
* Inform when a decision level changes
*/
private boolean tagDl;
/**
* Create lazily built implication graph
* @param model the model that uses this
*/
LazyImplications(Model model) {
nbEntries = 0;
size = model.getEnvironment().makeInt(0);
size._set(0, 0); // to force history manually -- required when created during the search
entries = new Entry[16];
rootEntries = new HashMap<>(16, .5f);
init(model);
}
@Override
public void init(Model model) {
IntVar[] ivars = model.retrieveIntVars(true);
for (IntVar var : ivars) {
ensureCapacity();
Entry root = entries[nbEntries] = new Entry();
root.set(var, Cause.Null, IntEventType.VOID.getMask(), 0, nbEntries, nbEntries,1);
root.getD().copyFrom(var);
root.d.lock();
var.createLit(root.d);
rootEntries.put(var, root);
nbEntries++;
}
size.set(nbEntries);
}
@Override
public void reset(){
synchronize(rootEntries.size());
}
/**
* @return true if links between nodes in this graph are correct
*/
private boolean checkIntegrity() {
for (Entry r : rootEntries.values()) {
int dec = nbEntries;
Entry prev = entries[r.p];
if(prev.i > dec) return false;
while (dec > 0 && prev != r) {
prev = entries[prev.p];
dec--;
}
if (dec == 0) return false;
}
return true;
}
/**
* Remove node below upto in the graph, and reconnect the new leaves with their root node.
* @param upto last correct node
*/
private void synchronize(int upto) {
for (int p = upto; p < nbEntries; p++) {
Entry e = entries[p];
e.getD().unlock();
Entry root = rootEntries.get(e.v);
if (root.p >= upto) {
root.setPrev(e.p);
}
}
nbEntries = upto;
assert !XParameters.DEBUG_INTEGRITY || checkIntegrity();
}
@Override
public void tagDecisionLevel() {
tagDl = true;
}
@Override
public void undoLastEvent() {
Entry toUndo = entries[--nbEntries];
rootEntries.get(toUndo.v).p = toUndo.p;
}
/**
* Make sure that a new entry can be added into this graph
*/
private void ensureCapacity() {
if (nbEntries >= entries.length) {
int oldCapacity = entries.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
Entry[] entBigger = new Entry[newCapacity];
System.arraycopy(entries, 0, entBigger, 0, oldCapacity);
entries = entBigger;
}
}
/**
* Return true if two entries, based on the same variable, can be merged.
* It depends on {@link XParameters#MERGE_CONDITIONS} which can be set to:
*
* -
* 0: merge is disabled
*
* -
* 1: merge two consecutive entries with the same variable and cause
*
* -
* 2: merge two entries with the same variable and cause,
* as long as they are done in the same filtering call.
*
*
*
* @param prev previous entry to merge with
* @param cause cause of the current event to merge into prev
* @return true if two entries can be merged into a single one.
*/
@SuppressWarnings("ConstantConditions")
private boolean mergeConditions(Entry prev, ICause cause) {
switch (XParameters.MERGE_CONDITIONS){
default:
case 0:
return false;
case 1:
return nbEntries - 1 == prev.i && cause == prev.c;
}
}
/**
* Merge two consecutive entries as long as they are based on the same variable and cause.
* The domain and mask are merged.
* @param evt event received
* @param one value removed, new lower bound, new upper bound or singleton value, wrt to evt
* @param nentry entry to merge with
*/
private void mergeEntry(IntEventType evt, int one, Entry nentry){
nentry.m |= evt.getMask();
nentry.getD().unlock();
mergeDomain(nentry.getD(), evt, one);
nentry.getD().lock();
}
/**
* Update a domain wrt a given event and its specialization
* @param dom domain to update
* @param mask event mask
* @param one an int (value removed, new bound, or singleton)
*/
private static void mergeDomain(IntIterableRangeSet dom, IntEventType mask, int one) {
switch (mask) {
case VOID:
case BOUND:
throw new Error("Unknown case "+ mask);
case INSTANTIATE:
dom.retainBetween(one, one);
break;
case REMOVE:
dom.remove(one);
break;
case INCLOW:
dom.removeBetween(dom.min(), one - 1);
break;
case DECUPP:
dom.removeBetween(one + 1, dom.max());
break;
}
}
/**
* Create a domain wrt a given event and its specialization
* @param to domain to create
* @param from domain to read
* @param mask event mask
* @param one an int (value removed, new bound, or singleton)
*/
private static void createDomain(IntIterableRangeSet to, IntIterableRangeSet from, IntEventType mask, int one) {
switch (mask) {
case VOID:
case BOUND:
throw new Error("Unknown case VOID");
case REMOVE:
IntIterableSetUtils.unionOf(to, from);
to.remove(one);
break;
case INCLOW:
IntIterableSetUtils.intersection(to, from, one, from.max());
break;
case DECUPP:
IntIterableSetUtils.intersection(to, from, from.min(), one);
break;
case INSTANTIATE:
IntIterableSetUtils.intersection(to, from, one, one);
break;
}
}
/**
* Create a new entry in this graph
* @param var a variable
* @param cause the cause of var modification
* @param evt the type of event received
* @param one value removed, new lower bound, new upper bound or singleton value, wrt to evt
* @param root its root node
* @param prev its predecessor
*/
private void addEntry(IntVar var, ICause cause, IntEventType evt, int one,
Entry root, Entry prev){
ensureCapacity();
// create entry
Entry nentry = entries[nbEntries];
if (nentry == null) {
nentry = entries[nbEntries] = new Entry();
} else {
nentry.getD().clear();
}
int dl = entries[nbEntries-1].dl;
if(tagDl){
tagDl = false;
dl++;
}
nentry.set(var, cause, evt.getMask(), one, nbEntries, prev.i, dl);
// make a (weak) copy of prev domain and update it wrt to current event
createDomain(nentry.getD(), prev.d, evt, one);
nentry.getD().lock();
// connect everything
root.setPrev(nbEntries);
size.add(1);
nbEntries++;
}
/**
* @implSpec
* Consecutive events for the same couple (variable, cause) are merged into a single one.
*/
@Override
public void pushEvent(IntVar var, ICause cause, IntEventType evt, int one, int two, int three) {
int size_ = size.get();
if (nbEntries != size_) {
synchronize(size_);
}
Entry root = rootEntries.get(var);
if (root == null) {
throw new Error("Unknown variable. This happens when a constraint is added after the call to `solver.setLearningClause();`");
}
int pidx = root.p;
Entry prev = entries[pidx];
assert prev != null;
assert prev.v == var;
if(mergeConditions(prev, cause)){
mergeEntry(evt, one, prev);
}else{
addEntry(var, cause, evt, one, root, prev);
}
assert !XParameters.DEBUG_INTEGRITY || checkIntegrity();
}
/**
* Find the right-most node, before p, in this,
* such that var matches the node.
* @param var a variable
* @return right-most position of var between [0,p] in this
*/
int rightmostNode(int limit, IntVar var) {
if(var.isBool()){
Entry root = rootEntries.get(var);
int ri = root.i;
assert ri < limit :"impossible right-most search";
// consider the case where the variable failed
if(root.p >= limit){
root = entries[root.p];
}
return root.p < limit ? root.p : ri;
}else {
// two ways of looking for the node
// 1. reverse-iteration over all nodes, starting from 'limit-1'
int pos = limit - 1;
// 2. reverse-iteration over nodes of var, starting from 'root.p'
// (presumably far away from limit)
int prev = rootEntries.get(var).p;
while (pos > 0 && entries[pos].v != var && prev > limit) {
pos--;
prev = entries[prev].p;
}
return prev > limit ? pos: prev;
}
}
@Override
public int size() {
return size.get();
}
@Override
public void collectNodesFromConflict(ContradictionException cft, ValueSortedMap front) {
if (cft.v != null) {
Entry root = rootEntries.get(cft.v);
assert entries[root.p].c == cft.c;
front.put((IntVar) cft.v, root.p);
} else {
cft.c.forEachIntVar(v -> {
Entry root = rootEntries.get(v);
front.put(root.v, root.p);
});
}
}
@Override
public void predecessorsOf(int p, ValueSortedMap front) {
Entry entry = entries[p];
ICause cause = entry.c;
// add the predecessor of 'p'
front.put(entry.v, entry.p);
cause.forEachIntVar(v -> findPredecessor(front, v, p));
}
/**
* Find the direct predecessor of a node, declared on variable vi, starting from node at
* position p.
* If a variable-based node already exists in front, then this node is used to look for the predecessor,
* assuming that it is below p (otherwise, this node the predecessor we are looking for).
* Otherwise, there is no node based on vi in front and the rightmost node above
* p, starting from the predecessor of its root node, is added.
* @param front the set to update
* @param vi the variable to look the predecessor for
* @param p the rightmost position of the node (below means outdated node).
*/
public void findPredecessor(ValueSortedMap front, IntVar vi, int p) {
int cpos = front.getValueOrDefault(vi, Integer.MAX_VALUE);
if(cpos < Integer.MAX_VALUE) {
while (cpos > p) {
cpos = entries[cpos].p;
}
front.replace(vi, cpos);
}else {
front.put(vi, rightmostNode(p, vi));
}
}
@Override
public ICause getCauseAt(int idx) {
return entries[idx].c;
}
@Override
public int getEventMaskAt(int idx) {
return entries[idx].m;
}
@Override
public IntVar getIntVarAt(int idx) {
return entries[idx].v;
}
@Override
public int getValueAt(int idx) {
assert XParameters.MERGE_CONDITIONS == 0;
return entries[idx].e;
}
@Override
public int getDecisionLevelAt(int idx) {
return entries[idx].dl;
}
@Override
public IntIterableRangeSet getDomainAt(int idx) {
return entries[idx].d;
}
@Override
public int getPredecessorOf(int idx) {
return entries[idx].p;
}
@Override
public IntIterableRangeSet getRootDomain(IntVar var) {
return rootEntries.get(var).d;
}
@Override
public void copyComplementSet(IntVar var, IntIterableRangeSet set, IntIterableRangeSet dest) {
dest.copyFrom(rootEntries.get(var).d);
dest.removeAll(set);
}
}
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