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bab.hh
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1 /* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
2 /*
3  * Main authors:
4  * Christian Schulte <schulte@gecode.org>
5  *
6  * Contributing authors:
7  * Guido Tack <tack@gecode.org>
8  *
9  * Copyright:
10  * Christian Schulte, 2004
11  * Guido Tack, 2004
12  *
13  * Last modified:
14  * $Date: 2015-03-20 15:37:34 +0100 (Fri, 20 Mar 2015) $ by $Author: schulte $
15  * $Revision: 14471 $
16  *
17  * This file is part of Gecode, the generic constraint
18  * development environment:
19  * http://www.gecode.org
20  *
21  * Permission is hereby granted, free of charge, to any person obtaining
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41 
42 #ifndef __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
43 #define __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
44 
45 #include <gecode/search.hh>
46 #include <gecode/search/support.hh>
47 #include <gecode/search/worker.hh>
49 
50 namespace Gecode { namespace Search { namespace Sequential {
51 
53  class BAB : public Worker {
54  private:
56  Options opt;
58  Path path;
60  Space* cur;
62  unsigned int d;
64  int mark;
66  Space* best;
67  public:
69  BAB(Space* s, const Options& o);
71  Space* next(void);
73  Statistics statistics(void) const;
75  void reset(Space* s);
77  NoGoods& nogoods(void);
79  ~BAB(void);
80  };
81 
83  BAB::BAB(Space* s, const Options& o)
84  : opt(o), path(opt.nogoods_limit), d(0), mark(0), best(NULL) {
85  if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
86  fail++;
87  cur = NULL;
88  if (!o.clone)
89  delete s;
90  } else {
91  cur = snapshot(s,opt);
92  }
93  }
94 
96  BAB::next(void) {
97  /*
98  * The engine maintains the following invariant:
99  * - If the current space (cur) is not NULL, the path always points
100  * to exactly that space.
101  * - If the current space (cur) is NULL, the path always points
102  * to the next space (if there is any).
103  *
104  * This invariant is needed so that no-goods can be extracted properly
105  * when the engine is stopped or has found a solution.
106  *
107  * An additional invariant maintained by the engine is:
108  * For all nodes stored at a depth less than mark, there
109  * is no guarantee of betterness. For those above the mark,
110  * betterness is guaranteed.
111  *
112  */
113  start();
114  while (true) {
115  if (stop(opt))
116  return NULL;
117  // Recompute and add constraint if necessary
118  while (cur == NULL) {
119  if (path.empty())
120  return NULL;
121  cur = path.recompute(d,opt.a_d,*this,*best,mark);
122  if (cur != NULL)
123  break;
124  path.next();
125  }
126  node++;
127  switch (cur->status(*this)) {
128  case SS_FAILED:
129  fail++;
130  delete cur;
131  cur = NULL;
132  path.next();
133  break;
134  case SS_SOLVED:
135  // Deletes all pending branchers
136  (void) cur->choice();
137  delete best;
138  best = cur;
139  cur = NULL;
140  path.next();
141  mark = path.entries();
142  return best->clone();
143  case SS_BRANCH:
144  {
145  Space* c;
146  if ((d == 0) || (d >= opt.c_d)) {
147  c = cur->clone();
148  d = 1;
149  } else {
150  c = NULL;
151  d++;
152  }
153  const Choice* ch = path.push(*this,cur,c);
154  cur->commit(*ch,0);
155  break;
156  }
157  default:
158  GECODE_NEVER;
159  }
160  }
161  GECODE_NEVER;
162  return NULL;
163  }
164 
166  BAB::statistics(void) const {
167  return *this;
168  }
169 
170  forceinline void
172  delete best;
173  best = NULL;
174  path.reset();
175  d = 0;
176  mark = 0;
177  delete cur;
178  if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
179  delete s;
180  cur = NULL;
181  } else {
182  cur = s;
183  }
184  Worker::reset();
185  }
186 
188  BAB::nogoods(void) {
189  return path;
190  }
191 
192  forceinline
193  BAB::~BAB(void) {
194  path.reset();
195  delete best;
196  delete cur;
197  }
198 
199 }}}
200 
201 #endif
202 
203 // STATISTICS: search-sequential
unsigned int a_d
Create a clone during recomputation if distance is greater than a_d (adaptive distance) ...
Definition: search.hh:458
Space must be branched (at least one brancher left)
Definition: core.hpp:1303
Search engine statistics
Definition: search.hh:136
unsigned int c_d
Create a clone after every c_d commits (commit distance)
Definition: search.hh:456
Space * clone(bool share=true, CloneStatistics &stat=unused_clone) const
Clone space.
Definition: core.hpp:2854
Search engine options
Definition: search.hh:449
const Choice * push(Worker &stat, Space *s, Space *c)
Push space c (a clone of s or NULL)
Definition: path.hh:222
Depth-first path (stack of edges) supporting recomputation.
Definition: path.hh:61
~BAB(void)
Destructor.
Definition: bab.hh:193
unsigned long int fail
Number of failed nodes in search tree.
Definition: search.hh:139
void path(Home home, int offset, const IntVarArgs &x, IntVar s, IntVar e, IntConLevel icl)
Post propagator such that x forms a Hamiltonian path.
Definition: circuit.cpp:128
void * mark(void *p)
Return marked pointer for p.
BAB(Space *s, const Options &o)
Initialize with space s and search options o.
Definition: bab.hh:83
Computation spaces.
Definition: core.hpp:1362
Implementation of depth-first branch-and-bound search engine.
Definition: bab.hh:53
NoGoods & nogoods(void)
Return no-goods.
Definition: bab.hh:188
Gecode::IntSet d(v, 7)
int entries(void) const
Return number of entries on stack.
Definition: path.hh:270
void start(void)
Reset stop information.
Definition: worker.hh:78
Gecode::FloatVal c(-8, 8)
Space * next(void)
Search for next better solution
Definition: bab.hh:96
Options opt
The options.
Definition: test.cpp:101
Statistics statistics(void) const
Return statistics.
Definition: bab.hh:166
Space * recompute(unsigned int &d, unsigned int a_d, Worker &s)
Recompute space according to path.
Definition: path.hh:290
void commit(const Choice &c, unsigned int a, CommitStatistics &stat=unused_commit)
Commit choice c for alternative a.
Definition: core.hpp:2862
bool clone
Whether engines create a clone when being initialized.
Definition: search.hh:452
void reset(void)
Reset stack.
Definition: path.hh:284
Search worker statistics
Definition: worker.hh:48
Choice for performing commit
Definition: core.hpp:1036
No-goods recorded from restarts.
Definition: core.hpp:1240
#define forceinline
Definition: config.hpp:132
void next(void)
Generate path for next node.
Definition: path.hh:234
SpaceStatus status(StatusStatistics &stat=unused_status)
Query space status.
Definition: core.cpp:252
Space * snapshot(Space *s, const Options &o, bool share=true)
Clone space s dependening on options o.
Definition: support.hh:73
unsigned long int node
Number of nodes expanded.
Definition: search.hh:141
const unsigned int nogoods_limit
Depth limit for no-good generation during search.
Definition: search.hh:107
Space is failed
Definition: core.hpp:1301
const Choice * choice(void)
Create new choice for current brancher.
Definition: core.cpp:366
#define GECODE_NEVER
Assert that this command is never executed.
Definition: macros.hpp:60
bool stop(const Options &o)
Check whether engine must be stopped.
Definition: worker.hh:83
bool empty(void) const
Test whether path is empty.
Definition: path.hh:251
void reset(void)
Reset.
Definition: statistics.hpp:43
Space is solved (no brancher left)
Definition: core.hpp:1302