COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/hugo/preflow.h @ 919:6153d9cf78c6

Last change on this file since 919:6153d9cf78c6 was 911:89a4fbb99cad, checked in by Alpar Juttner, 20 years ago

Fix many doxygen command bugs.

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1/* -*- C++ -*-
2 * src/hugo/preflow.h - Part of HUGOlib, a generic C++ optimization library
3 *
4 * Copyright (C) 2004 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Combinatorial Optimization Research Group, EGRES).
6 *
7 * Permission to use, modify and distribute this software is granted
8 * provided that this copyright notice appears in all copies. For
9 * precise terms see the accompanying LICENSE file.
10 *
11 * This software is provided "AS IS" with no warranty of any kind,
12 * express or implied, and with no claim as to its suitability for any
13 * purpose.
14 *
15 */
16
17#ifndef HUGO_PREFLOW_H
18#define HUGO_PREFLOW_H
19
20#include <vector>
21#include <queue>
22
23#include <hugo/invalid.h>
24#include <hugo/maps.h>
25
26/// \file
27/// \ingroup flowalgs
28/// Implementation of the preflow algorithm.
29
30namespace hugo {
31
32  /// \addtogroup flowalgs
33  /// @{                                                   
34
35  ///%Preflow algorithms class.
36
37  ///This class provides an implementation of the \e preflow \e
38  ///algorithm producing a flow of maximum value in a directed
39  ///graph. The preflow algorithms are the fastest max flow algorithms
40  ///up to now. The \e source node, the \e target node, the \e
41  ///capacity of the edges and the \e starting \e flow value of the
42  ///edges should be passed to the algorithm through the
43  ///constructor. It is possible to change these quantities using the
44  ///functions \ref setSource, \ref setTarget, \ref setCap and \ref
45  ///setFlow.
46  ///
47  ///After running \ref hugo::Preflow::phase1() "phase1()"
48  ///or \ref hugo::Preflow::run() "run()", the actual flow
49  ///value can be obtained by calling \ref flowValue(). The minimum
50  ///value cut can be written into a <tt>bool</tt> node map by
51  ///calling \ref minCut(). (\ref minMinCut() and \ref maxMinCut() writes
52  ///the inclusionwise minimum and maximum of the minimum value cuts,
53  ///resp.)
54  ///
55  ///\param Graph The directed graph type the algorithm runs on.
56  ///\param Num The number type of the capacities and the flow values.
57  ///\param CapMap The capacity map type.
58  ///\param FlowMap The flow map type.
59  ///
60  ///\author Jacint Szabo
61  template <typename Graph, typename Num,
62            typename CapMap=typename Graph::template EdgeMap<Num>,
63            typename FlowMap=typename Graph::template EdgeMap<Num> >
64  class Preflow {
65  protected:
66    typedef typename Graph::Node Node;
67    typedef typename Graph::NodeIt NodeIt;
68    typedef typename Graph::EdgeIt EdgeIt;
69    typedef typename Graph::OutEdgeIt OutEdgeIt;
70    typedef typename Graph::InEdgeIt InEdgeIt;
71
72    typedef typename Graph::template NodeMap<Node> NNMap;
73    typedef typename std::vector<Node> VecNode;
74
75    const Graph* g;
76    Node s;
77    Node t;
78    const CapMap* capacity;
79    FlowMap* flow;
80    int n;      //the number of nodes of G
81   
82    typename Graph::template NodeMap<int> level; 
83    typename Graph::template NodeMap<Num> excess;
84
85    // constants used for heuristics
86    static const int H0=20;
87    static const int H1=1;
88
89    public:
90
91    ///Indicates the property of the starting flow map.
92
93    ///Indicates the property of the starting flow map. The meanings are as follows:
94    ///- \c ZERO_FLOW: constant zero flow
95    ///- \c GEN_FLOW: any flow, i.e. the sum of the in-flows equals to
96    ///the sum of the out-flows in every node except the \e source and
97    ///the \e target.
98    ///- \c PRE_FLOW: any preflow, i.e. the sum of the in-flows is at
99    ///least the sum of the out-flows in every node except the \e source.
100    ///- \c NO_FLOW: indicates an unspecified edge map. \c flow will be
101    ///set to the constant zero flow in the beginning of
102    ///the algorithm in this case.
103    ///
104    enum FlowEnum{
105      NO_FLOW,
106      ZERO_FLOW,
107      GEN_FLOW,
108      PRE_FLOW
109    };
110
111    ///Indicates the state of the preflow algorithm.
112
113    ///Indicates the state of the preflow algorithm. The meanings are as follows:
114    ///- \c AFTER_NOTHING: before running the algorithm or at an unspecified state.
115    ///- \c AFTER_PREFLOW_PHASE_1: right after running \c phase1
116    ///- \c AFTER_PREFLOW_PHASE_2: after running \ref phase2()
117    ///
118    enum StatusEnum {
119      AFTER_NOTHING,
120      AFTER_PREFLOW_PHASE_1,     
121      AFTER_PREFLOW_PHASE_2
122    };
123   
124    protected:
125      FlowEnum flow_prop;
126    StatusEnum status; // Do not needle this flag only if necessary.
127   
128  public:
129    ///The constructor of the class.
130
131    ///The constructor of the class.
132    ///\param _G The directed graph the algorithm runs on.
133    ///\param _s The source node.
134    ///\param _t The target node.
135    ///\param _capacity The capacity of the edges.
136    ///\param _flow The flow of the edges.
137    ///Except the graph, all of these parameters can be reset by
138    ///calling \ref setSource, \ref setTarget, \ref setCap and \ref
139    ///setFlow, resp.
140      Preflow(const Graph& _G, Node _s, Node _t,
141              const CapMap& _capacity, FlowMap& _flow) :
142        g(&_G), s(_s), t(_t), capacity(&_capacity),
143        flow(&_flow), n(_G.nodeNum()), level(_G), excess(_G,0),
144        flow_prop(NO_FLOW), status(AFTER_NOTHING) { }
145
146
147                                                                             
148    ///Runs the preflow algorithm. 
149
150    ///Runs the preflow algorithm.
151    ///
152    void run() {
153      phase1(flow_prop);
154      phase2();
155    }
156   
157    ///Runs the preflow algorithm. 
158   
159    ///Runs the preflow algorithm.
160    ///\pre The starting flow map must be
161    /// - a constant zero flow if \c fp is \c ZERO_FLOW,
162    /// - an arbitrary flow if \c fp is \c GEN_FLOW,
163    /// - an arbitrary preflow if \c fp is \c PRE_FLOW,
164    /// - any map if \c fp is NO_FLOW.
165    ///If the starting flow map is a flow or a preflow then
166    ///the algorithm terminates faster.
167    void run(FlowEnum fp) {
168      flow_prop=fp;
169      run();
170    }
171     
172    ///Runs the first phase of the preflow algorithm.
173
174    ///The preflow algorithm consists of two phases, this method runs the
175    ///first phase. After the first phase the maximum flow value and a
176    ///minimum value cut can already be computed, though a maximum flow
177    ///is not yet obtained. So after calling this method \ref flowValue
178    ///and \ref minCut gives proper results.
179    ///\warning \ref minMinCut and \ref maxMinCut do not
180    ///give minimum value cuts unless calling \ref phase2.
181    ///\pre The starting flow must be
182    /// - a constant zero flow if \c fp is \c ZERO_FLOW,
183    /// - an arbitary flow if \c fp is \c GEN_FLOW,
184    /// - an arbitary preflow if \c fp is \c PRE_FLOW,
185    /// - any map if \c fp is NO_FLOW.
186    void phase1(FlowEnum fp)
187    {
188      flow_prop=fp;
189      phase1();
190    }
191
192   
193    ///Runs the first phase of the preflow algorithm.
194
195    ///The preflow algorithm consists of two phases, this method runs the
196    ///first phase. After the first phase the maximum flow value and a
197    ///minimum value cut can already be computed, though a maximum flow
198    ///is not yet obtained. So after calling this method \ref flowValue
199    ///and \ref MinCut() gives proper results.
200    ///\warning \ref minCut(), \ref minMinCut() and \ref maxMinCut() do not
201    ///give minimum value cuts unless calling \ref phase2().
202    void phase1()
203    {
204      int heur0=(int)(H0*n);  //time while running 'bound decrease'
205      int heur1=(int)(H1*n);  //time while running 'highest label'
206      int heur=heur1;         //starting time interval (#of relabels)
207      int numrelabel=0;
208
209      bool what_heur=1;
210      //It is 0 in case 'bound decrease' and 1 in case 'highest label'
211
212      bool end=false;
213      //Needed for 'bound decrease', true means no active
214      //nodes are above bound b.
215
216      int k=n-2;  //bound on the highest level under n containing a node
217      int b=k;    //bound on the highest level under n of an active node
218
219      VecNode first(n, INVALID);
220      NNMap next(*g, INVALID);
221
222      NNMap left(*g, INVALID);
223      NNMap right(*g, INVALID);
224      VecNode level_list(n,INVALID);
225      //List of the nodes in level i<n, set to n.
226
227      preflowPreproc(first, next, level_list, left, right);
228
229      //Push/relabel on the highest level active nodes.
230      while ( true ) {
231        if ( b == 0 ) {
232          if ( !what_heur && !end && k > 0 ) {
233            b=k;
234            end=true;
235          } else break;
236        }
237
238        if ( first[b]==INVALID ) --b;
239        else {
240          end=false;
241          Node w=first[b];
242          first[b]=next[w];
243          int newlevel=push(w, next, first);
244          if ( excess[w] > 0 ) relabel(w, newlevel, first, next, level_list,
245                                       left, right, b, k, what_heur);
246
247          ++numrelabel;
248          if ( numrelabel >= heur ) {
249            numrelabel=0;
250            if ( what_heur ) {
251              what_heur=0;
252              heur=heur0;
253              end=false;
254            } else {
255              what_heur=1;
256              heur=heur1;
257              b=k;
258            }
259          }
260        }
261      }
262      flow_prop=PRE_FLOW;
263      status=AFTER_PREFLOW_PHASE_1;
264    }
265    // Heuristics:
266    //   2 phase
267    //   gap
268    //   list 'level_list' on the nodes on level i implemented by hand
269    //   stack 'active' on the active nodes on level i     
270    //   runs heuristic 'highest label' for H1*n relabels
271    //   runs heuristic 'bound decrease' for H0*n relabels, starts with 'highest label'
272    //   Parameters H0 and H1 are initialized to 20 and 1.
273
274
275    ///Runs the second phase of the preflow algorithm.
276
277    ///The preflow algorithm consists of two phases, this method runs
278    ///the second phase. After calling \ref phase1 and then
279    ///\ref phase2 the methods \ref flowValue, \ref minCut,
280    ///\ref minMinCut and \ref maxMinCut give proper results.
281    ///\pre \ref phase1 must be called before.
282    void phase2()
283    {
284
285      int k=n-2;  //bound on the highest level under n containing a node
286      int b=k;    //bound on the highest level under n of an active node
287
288   
289      VecNode first(n, INVALID);
290      NNMap next(*g, INVALID);
291      level.set(s,0);
292      std::queue<Node> bfs_queue;
293      bfs_queue.push(s);
294
295      while ( !bfs_queue.empty() ) {
296
297        Node v=bfs_queue.front();
298        bfs_queue.pop();
299        int l=level[v]+1;
300
301        for(InEdgeIt e(*g,v); e!=INVALID; ++e) {
302          if ( (*capacity)[e] <= (*flow)[e] ) continue;
303          Node u=g->tail(e);
304          if ( level[u] >= n ) {
305            bfs_queue.push(u);
306            level.set(u, l);
307            if ( excess[u] > 0 ) {
308              next.set(u,first[l]);
309              first[l]=u;
310            }
311          }
312        }
313
314        for(OutEdgeIt e(*g,v); e!=INVALID; ++e) {
315          if ( 0 >= (*flow)[e] ) continue;
316          Node u=g->head(e);
317          if ( level[u] >= n ) {
318            bfs_queue.push(u);
319            level.set(u, l);
320            if ( excess[u] > 0 ) {
321              next.set(u,first[l]);
322              first[l]=u;
323            }
324          }
325        }
326      }
327      b=n-2;
328
329      while ( true ) {
330
331        if ( b == 0 ) break;
332        if ( first[b]==INVALID ) --b;
333        else {
334          Node w=first[b];
335          first[b]=next[w];
336          int newlevel=push(w,next, first);
337         
338          //relabel
339          if ( excess[w] > 0 ) {
340            level.set(w,++newlevel);
341            next.set(w,first[newlevel]);
342            first[newlevel]=w;
343            b=newlevel;
344          }
345        }
346      } // while(true)
347      flow_prop=GEN_FLOW;
348      status=AFTER_PREFLOW_PHASE_2;
349    }
350
351    /// Returns the value of the maximum flow.
352
353    /// Returns the value of the maximum flow by returning the excess
354    /// of the target node \c t. This value equals to the value of
355    /// the maximum flow already after running \ref phase1.
356    Num flowValue() const {
357      return excess[t];
358    }
359
360
361    ///Returns a minimum value cut.
362
363    ///Sets \c M to the characteristic vector of a minimum value
364    ///cut. This method can be called both after running \ref
365    ///phase1 and \ref phase2. It is much faster after
366    ///\ref phase1.  \pre M should be a bool-valued node-map. \pre
367    ///If \ref minCut() is called after \ref phase2() then M should
368    ///be initialized to false.
369    template<typename _CutMap>
370    void minCut(_CutMap& M) const {
371      switch ( status ) {
372        case AFTER_PREFLOW_PHASE_1:
373        for(NodeIt v(*g); v!=INVALID; ++v) {
374          if (level[v] < n) {
375            M.set(v, false);
376          } else {
377            M.set(v, true);
378          }
379        }
380        break;
381        case AFTER_PREFLOW_PHASE_2:
382        minMinCut(M);
383        break;
384        case AFTER_NOTHING:
385        break;
386      }
387    }
388
389    ///Returns the inclusionwise minimum of the minimum value cuts.
390
391    ///Sets \c M to the characteristic vector of the minimum value cut
392    ///which is inclusionwise minimum. It is computed by processing a
393    ///bfs from the source node \c s in the residual graph.  \pre M
394    ///should be a node map of bools initialized to false.  \pre \ref
395    ///phase2 should already be run.
396    template<typename _CutMap>
397    void minMinCut(_CutMap& M) const {
398
399      std::queue<Node> queue;
400      M.set(s,true);
401      queue.push(s);
402     
403      while (!queue.empty()) {
404        Node w=queue.front();
405        queue.pop();
406       
407        for(OutEdgeIt e(*g,w) ; e!=INVALID; ++e) {
408          Node v=g->head(e);
409          if (!M[v] && (*flow)[e] < (*capacity)[e] ) {
410            queue.push(v);
411            M.set(v, true);
412          }
413        }
414       
415        for(InEdgeIt e(*g,w) ; e!=INVALID; ++e) {
416          Node v=g->tail(e);
417          if (!M[v] && (*flow)[e] > 0 ) {
418            queue.push(v);
419            M.set(v, true);
420          }
421        }
422      }
423    }
424   
425    ///Returns the inclusionwise maximum of the minimum value cuts.
426
427    ///Sets \c M to the characteristic vector of the minimum value cut
428    ///which is inclusionwise maximum. It is computed by processing a
429    ///backward bfs from the target node \c t in the residual graph.
430    ///\pre \ref phase2() or run() should already be run.
431    template<typename _CutMap>
432    void maxMinCut(_CutMap& M) const {
433
434      for(NodeIt v(*g) ; v!=INVALID; ++v) M.set(v, true);
435
436      std::queue<Node> queue;
437
438      M.set(t,false);
439      queue.push(t);
440
441      while (!queue.empty()) {
442        Node w=queue.front();
443        queue.pop();
444
445        for(InEdgeIt e(*g,w) ; e!=INVALID; ++e) {
446          Node v=g->tail(e);
447          if (M[v] && (*flow)[e] < (*capacity)[e] ) {
448            queue.push(v);
449            M.set(v, false);
450          }
451        }
452
453        for(OutEdgeIt e(*g,w) ; e!=INVALID; ++e) {
454          Node v=g->head(e);
455          if (M[v] && (*flow)[e] > 0 ) {
456            queue.push(v);
457            M.set(v, false);
458          }
459        }
460      }
461    }
462
463    ///Sets the source node to \c _s.
464
465    ///Sets the source node to \c _s.
466    ///
467    void setSource(Node _s) {
468      s=_s;
469      if ( flow_prop != ZERO_FLOW ) flow_prop=NO_FLOW;
470      status=AFTER_NOTHING;
471    }
472
473    ///Sets the target node to \c _t.
474
475    ///Sets the target node to \c _t.
476    ///
477    void setTarget(Node _t) {
478      t=_t;
479      if ( flow_prop == GEN_FLOW ) flow_prop=PRE_FLOW;
480      status=AFTER_NOTHING;
481    }
482
483    /// Sets the edge map of the capacities to _cap.
484
485    /// Sets the edge map of the capacities to _cap.
486    ///
487    void setCap(const CapMap& _cap) {
488      capacity=&_cap;
489      status=AFTER_NOTHING;
490    }
491
492    /// Sets the edge map of the flows to _flow.
493
494    /// Sets the edge map of the flows to _flow.
495    ///
496    void setFlow(FlowMap& _flow) {
497      flow=&_flow;
498      flow_prop=NO_FLOW;
499      status=AFTER_NOTHING;
500    }
501
502
503  private:
504
505    int push(Node w, NNMap& next, VecNode& first) {
506
507      int lev=level[w];
508      Num exc=excess[w];
509      int newlevel=n;       //bound on the next level of w
510
511      for(OutEdgeIt e(*g,w) ; e!=INVALID; ++e) {
512        if ( (*flow)[e] >= (*capacity)[e] ) continue;
513        Node v=g->head(e);
514
515        if( lev > level[v] ) { //Push is allowed now
516         
517          if ( excess[v]<=0 && v!=t && v!=s ) {
518            next.set(v,first[level[v]]);
519            first[level[v]]=v;
520          }
521
522          Num cap=(*capacity)[e];
523          Num flo=(*flow)[e];
524          Num remcap=cap-flo;
525         
526          if ( remcap >= exc ) { //A nonsaturating push.
527           
528            flow->set(e, flo+exc);
529            excess.set(v, excess[v]+exc);
530            exc=0;
531            break;
532
533          } else { //A saturating push.
534            flow->set(e, cap);
535            excess.set(v, excess[v]+remcap);
536            exc-=remcap;
537          }
538        } else if ( newlevel > level[v] ) newlevel = level[v];
539      } //for out edges wv
540
541      if ( exc > 0 ) {
542        for(InEdgeIt e(*g,w) ; e!=INVALID; ++e) {
543         
544          if( (*flow)[e] <= 0 ) continue;
545          Node v=g->tail(e);
546
547          if( lev > level[v] ) { //Push is allowed now
548
549            if ( excess[v]<=0 && v!=t && v!=s ) {
550              next.set(v,first[level[v]]);
551              first[level[v]]=v;
552            }
553
554            Num flo=(*flow)[e];
555
556            if ( flo >= exc ) { //A nonsaturating push.
557
558              flow->set(e, flo-exc);
559              excess.set(v, excess[v]+exc);
560              exc=0;
561              break;
562            } else {  //A saturating push.
563
564              excess.set(v, excess[v]+flo);
565              exc-=flo;
566              flow->set(e,0);
567            }
568          } else if ( newlevel > level[v] ) newlevel = level[v];
569        } //for in edges vw
570
571      } // if w still has excess after the out edge for cycle
572
573      excess.set(w, exc);
574     
575      return newlevel;
576    }
577   
578   
579   
580    void preflowPreproc(VecNode& first, NNMap& next,
581                        VecNode& level_list, NNMap& left, NNMap& right)
582    {
583      for(NodeIt v(*g); v!=INVALID; ++v) level.set(v,n);
584      std::queue<Node> bfs_queue;
585     
586      if ( flow_prop == GEN_FLOW || flow_prop == PRE_FLOW ) {
587        //Reverse_bfs from t in the residual graph,
588        //to find the starting level.
589        level.set(t,0);
590        bfs_queue.push(t);
591       
592        while ( !bfs_queue.empty() ) {
593         
594          Node v=bfs_queue.front();
595          bfs_queue.pop();
596          int l=level[v]+1;
597         
598          for(InEdgeIt e(*g,v) ; e!=INVALID; ++e) {
599            if ( (*capacity)[e] <= (*flow)[e] ) continue;
600            Node w=g->tail(e);
601            if ( level[w] == n && w != s ) {
602              bfs_queue.push(w);
603              Node z=level_list[l];
604              if ( z!=INVALID ) left.set(z,w);
605              right.set(w,z);
606              level_list[l]=w;
607              level.set(w, l);
608            }
609          }
610         
611          for(OutEdgeIt e(*g,v) ; e!=INVALID; ++e) {
612            if ( 0 >= (*flow)[e] ) continue;
613            Node w=g->head(e);
614            if ( level[w] == n && w != s ) {
615              bfs_queue.push(w);
616              Node z=level_list[l];
617              if ( z!=INVALID ) left.set(z,w);
618              right.set(w,z);
619              level_list[l]=w;
620              level.set(w, l);
621            }
622          }
623        } //while
624      } //if
625
626
627      switch (flow_prop) {
628        case NO_FLOW: 
629        for(EdgeIt e(*g); e!=INVALID; ++e) flow->set(e,0);
630        case ZERO_FLOW:
631        for(NodeIt v(*g); v!=INVALID; ++v) excess.set(v,0);
632       
633        //Reverse_bfs from t, to find the starting level.
634        level.set(t,0);
635        bfs_queue.push(t);
636       
637        while ( !bfs_queue.empty() ) {
638         
639          Node v=bfs_queue.front();
640          bfs_queue.pop();
641          int l=level[v]+1;
642         
643          for(InEdgeIt e(*g,v) ; e!=INVALID; ++e) {
644            Node w=g->tail(e);
645            if ( level[w] == n && w != s ) {
646              bfs_queue.push(w);
647              Node z=level_list[l];
648              if ( z!=INVALID ) left.set(z,w);
649              right.set(w,z);
650              level_list[l]=w;
651              level.set(w, l);
652            }
653          }
654        }
655       
656        //the starting flow
657        for(OutEdgeIt e(*g,s) ; e!=INVALID; ++e) {
658          Num c=(*capacity)[e];
659          if ( c <= 0 ) continue;
660          Node w=g->head(e);
661          if ( level[w] < n ) {
662            if ( excess[w] <= 0 && w!=t ) { //putting into the stack
663              next.set(w,first[level[w]]);
664              first[level[w]]=w;
665            }
666            flow->set(e, c);
667            excess.set(w, excess[w]+c);
668          }
669        }
670        break;
671
672        case GEN_FLOW:
673        for(NodeIt v(*g); v!=INVALID; ++v) excess.set(v,0);
674        {
675          Num exc=0;
676          for(InEdgeIt e(*g,t) ; e!=INVALID; ++e) exc+=(*flow)[e];
677          for(OutEdgeIt e(*g,t) ; e!=INVALID; ++e) exc-=(*flow)[e];
678          excess.set(t,exc);
679        }
680
681        //the starting flow
682        for(OutEdgeIt e(*g,s); e!=INVALID; ++e) {
683          Num rem=(*capacity)[e]-(*flow)[e];
684          if ( rem <= 0 ) continue;
685          Node w=g->head(e);
686          if ( level[w] < n ) {
687            if ( excess[w] <= 0 && w!=t ) { //putting into the stack
688              next.set(w,first[level[w]]);
689              first[level[w]]=w;
690            }   
691            flow->set(e, (*capacity)[e]);
692            excess.set(w, excess[w]+rem);
693          }
694        }
695       
696        for(InEdgeIt e(*g,s); e!=INVALID; ++e) {
697          if ( (*flow)[e] <= 0 ) continue;
698          Node w=g->tail(e);
699          if ( level[w] < n ) {
700            if ( excess[w] <= 0 && w!=t ) {
701              next.set(w,first[level[w]]);
702              first[level[w]]=w;
703            } 
704            excess.set(w, excess[w]+(*flow)[e]);
705            flow->set(e, 0);
706          }
707        }
708        break;
709
710        case PRE_FLOW: 
711        //the starting flow
712        for(OutEdgeIt e(*g,s) ; e!=INVALID; ++e) {
713          Num rem=(*capacity)[e]-(*flow)[e];
714          if ( rem <= 0 ) continue;
715          Node w=g->head(e);
716          if ( level[w] < n ) flow->set(e, (*capacity)[e]);
717        }
718       
719        for(InEdgeIt e(*g,s) ; e!=INVALID; ++e) {
720          if ( (*flow)[e] <= 0 ) continue;
721          Node w=g->tail(e);
722          if ( level[w] < n ) flow->set(e, 0);
723        }
724       
725        //computing the excess
726        for(NodeIt w(*g); w!=INVALID; ++w) {
727          Num exc=0;
728          for(InEdgeIt e(*g,w); e!=INVALID; ++e) exc+=(*flow)[e];
729          for(OutEdgeIt e(*g,w); e!=INVALID; ++e) exc-=(*flow)[e];
730          excess.set(w,exc);
731         
732          //putting the active nodes into the stack
733          int lev=level[w];
734            if ( exc > 0 && lev < n && Node(w) != t ) {
735              next.set(w,first[lev]);
736              first[lev]=w;
737            }
738        }
739        break;
740      } //switch
741    } //preflowPreproc
742
743
744    void relabel(Node w, int newlevel, VecNode& first, NNMap& next,
745                 VecNode& level_list, NNMap& left,
746                 NNMap& right, int& b, int& k, bool what_heur )
747    {
748
749      int lev=level[w];
750
751      Node right_n=right[w];
752      Node left_n=left[w];
753
754      //unlacing starts
755      if ( right_n!=INVALID ) {
756        if ( left_n!=INVALID ) {
757          right.set(left_n, right_n);
758          left.set(right_n, left_n);
759        } else {
760          level_list[lev]=right_n;
761          left.set(right_n, INVALID);
762        }
763      } else {
764        if ( left_n!=INVALID ) {
765          right.set(left_n, INVALID);
766        } else {
767          level_list[lev]=INVALID;
768        }
769      }
770      //unlacing ends
771
772      if ( level_list[lev]==INVALID ) {
773
774        //gapping starts
775        for (int i=lev; i!=k ; ) {
776          Node v=level_list[++i];
777          while ( v!=INVALID ) {
778            level.set(v,n);
779            v=right[v];
780          }
781          level_list[i]=INVALID;
782          if ( !what_heur ) first[i]=INVALID;
783        }
784
785        level.set(w,n);
786        b=lev-1;
787        k=b;
788        //gapping ends
789
790      } else {
791
792        if ( newlevel == n ) level.set(w,n);
793        else {
794          level.set(w,++newlevel);
795          next.set(w,first[newlevel]);
796          first[newlevel]=w;
797          if ( what_heur ) b=newlevel;
798          if ( k < newlevel ) ++k;      //now k=newlevel
799          Node z=level_list[newlevel];
800          if ( z!=INVALID ) left.set(z,w);
801          right.set(w,z);
802          left.set(w,INVALID);
803          level_list[newlevel]=w;
804        }
805      }
806    } //relabel
807
808  };
809} //namespace hugo
810
811#endif //HUGO_PREFLOW_H
812
813
814
815
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