Last change on this file since 1025:3b1ad8bc21da was 986:e997802b855c, checked in by Alpar Juttner, 20 years ago

Naming changes:

• tail -> source
File size: 11.0 KB
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1#ifndef LEMON_PREFLOW_PUSH_HH
2#define LEMON_PREFLOW_PUSH_HH
3
4//#include <algorithm>
5#include <list>
6#include <vector>
7#include <queue>
8//#include "pf_hiba.hh"
9//#include <marci_list_graph.hh>
10//#include <marci_graph_traits.hh>
11#include <invalid.h>
12//#include <reverse_bfs.hh>
13
14using namespace std;
15
16namespace lemon {
17
18  template <typename Graph, typename T>
19  class preflow_push {
20
21    //Useful typedefs
22    typedef typename Graph::Node Node;
23    typedef typename Graph::NodeIt NodeIt;
24    typedef typename Graph::Edge Edge;
25    typedef typename Graph::OutEdgeIt OutEdgeIt;
26    typedef typename Graph::InEdgeIt InEdgeIt;
27
28
29    //---------------------------------------------
30    //Parameters of the algorithm
31    //---------------------------------------------
32    //Fully examine an active node until excess becomes 0
33    enum node_examination_t {examine_full, examine_to_relabel};
34    //No more implemented yet:, examine_only_one_edge};
35    node_examination_t node_examination;
36    //Which implementation to be used
37    enum implementation_t {impl_fifo, impl_highest_label};
38    //No more implemented yet:};
39    implementation_t implementation;
40    //---------------------------------------------
41    //Parameters of the algorithm
42    //---------------------------------------------
43
44  private:
45    //input
46    Graph& G;
47    Node s;
48    Node t;
49    typename Graph::EdgeMap<T> &capacity;
50
51    //output
52    typename Graph::EdgeMap<T> preflow;
53    T maxflow_value;
54
55    //auxiliary variables for computation
56    //The number of the nodes
57    int number_of_nodes;
58    //A nodemap for the level
59    typename Graph::NodeMap<int> level;
60    //A nodemap for the excess
61    typename Graph::NodeMap<T> excess;
62
63    //Number of nodes on each level
64    vector<int> num_of_nodes_on_level;
65
66    //For the FIFO implementation
67    list<Node> fifo_nodes;
68    //For 'highest label' implementation
69    int highest_active;
70    //int second_highest_active;
71    vector< list<Node> > active_nodes;
72
73  public:
74
75    //Constructing the object using the graph, source, sink and capacity vector
76    preflow_push(
77                      Graph& _G,
78                      Node _s,
79                      Node _t,
80                      typename Graph::EdgeMap<T> & _capacity)
81      : G(_G), s(_s), t(_t),
82        capacity(_capacity),
83        preflow(_G),
84        //Counting the number of nodes
85        //number_of_nodes(count(G.first<EachNodeIt>())),
86        number_of_nodes(G.nodeNum()),
87
88        level(_G),
89        excess(_G)//,
90        // Default constructor: active_nodes()
91    {
92      //Simplest parameter settings
93      node_examination = examine_full;//examine_to_relabel;//
94      //Which implementation to be usedexamine_full
95      implementation = impl_highest_label;//impl_fifo;
96
97      //
98      num_of_nodes_on_level.resize(2*number_of_nodes-1);
99      num_of_nodes_on_level.clear();
100
101      switch(implementation){
102      case impl_highest_label :{
103        active_nodes.clear();
104        active_nodes.resize(2*number_of_nodes-1);
105
106        break;
107      }
108      default:
109        break;
110      }
111
112    }
113
114    //Returns the value of a maximal flow
115    T run();
116
117    typename Graph::EdgeMap<T>  getmaxflow(){
118      return preflow;
119    }
120
121
122  private:
123    //For testing purposes only
124    //Lists the node_properties
125    void write_property_vector(typename Graph::NodeMap<T> a,
126                               //node_property_vector<Graph, T> a,
127                               char* prop_name="property"){
128      for(NodeIt i=G.template first<NodeIt>(); G.valid(i); G.next(i)) {
129        cout<<"Node id.: "<<G.id(i)<<", "<<prop_name<<" value: "<<a[i]<<endl;
130      }
131      cout<<endl;
132    }
133
134    //Modifies the excess of the node and makes sufficient changes
135    void modify_excess(const Node& a ,T v){
136      //T old_value=excess[a];
137      excess[a] += v;
138    }
139
140    //This private procedure is supposed to modify the preflow on edge j
141    //by value v (which can be positive or negative as well)
142    //and maintain the excess on the target and source
143    //Here we do not check whether this is possible or not
144    void modify_preflow(Edge j, const T& v){
145
146      //Modifiyng the edge
147      preflow[j] += v;
148
149
150      //Modifiyng the target
151      modify_excess(G.target(j),v);
152
153      //Modifiyng the source
154      modify_excess(G.source(j),-v);
155
156    }
157
158    //Gives the active node to work with
159    //(depending on the implementation to be used)
160    Node get_active_node(){
161
162
163      switch(implementation) {
164      case impl_highest_label : {
165
166        //First need to find the highest label for which there's an active node
167        while( highest_active>=0 && active_nodes[highest_active].empty() ){
168          --highest_active;
169        }
170
171        if( highest_active>=0) {
172
173
174          Node a=active_nodes[highest_active].front();
175          active_nodes[highest_active].pop_front();
176
177          return a;
178        }
179        else {
180          return INVALID;
181        }
182
183        break;
184
185      }
186      case impl_fifo : {
187
188        if( ! fifo_nodes.empty() ) {
189          Node a=fifo_nodes.front();
190          fifo_nodes.pop_front();
191          return a;
192        }
193        else {
194          return INVALID;
195        }
196        break;
197      }
198      }
199      //
200      return INVALID;
201    }
202
203    //Puts node 'a' among the active nodes
204    void make_active(const Node& a){
205      //s and t never become active
206      if (a!=s && a!= t){
207        switch(implementation){
208        case impl_highest_label :
209          active_nodes[level[a]].push_back(a);
210          break;
211        case impl_fifo :
212          fifo_nodes.push_back(a);
213          break;
214        }
215
216      }
217
218      //Update highest_active label
219      if (highest_active<level[a]){
220        highest_active=level[a];
221      }
222
223    }
224
225    //Changes the level of node a and make sufficent changes
226    void change_level_to(Node a, int new_value){
227      int seged = level[a];
228      level.set(a,new_value);
229      --num_of_nodes_on_level[seged];
230      ++num_of_nodes_on_level[new_value];
231    }
232
233    //Collection of things useful (or necessary) to do before running
234
235    void preprocess(){
236
237      //---------------------------------------
238      //Initialize parameters
239      //---------------------------------------
240
241      //Setting starting preflow, level and excess values to zero
242      //This can be important, if the algorithm is run more then once
243      for(NodeIt i=G.template first<NodeIt>(); G.valid(i); G.next(i)) {
244        level.set(i,0);
245        excess.set(i,0);
246        for(OutEdgeIt j=G.template first<OutEdgeIt>(i); G.valid(j); G.next(j))
247          preflow.set(j, 0);
248      }
249      num_of_nodes_on_level[0]=number_of_nodes;
250      highest_active=0;
251      //---------------------------------------
252      //Initialize parameters
253      //---------------------------------------
254
255
256      //------------------------------------
257      //This is the only part that uses BFS
258      //------------------------------------
259
260      /*Reverse_bfs from t, to find the starting level.*/
262      change_level_to(t,0);
263
264      std::queue<Node> bfs_queue;
265      bfs_queue.push(t);
266
267      while (!bfs_queue.empty()) {
268
269        Node v=bfs_queue.front();
270        bfs_queue.pop();
271        int l=level[v]+1;
272
273        InEdgeIt e;
274        for(G.first(e,v); G.valid(e); G.next(e)) {
275          Node w=G.source(e);
276          if ( level[w] == number_of_nodes && w != s ) {
277            bfs_queue.push(w);
278            //Node first=level_list[l];
279            //if ( G.valid(first) ) left.set(first,w);
280            //right.set(w,first);
281            //level_list[l]=w;
282            change_level_to(w, l);
283            //level.set(w, l);
284          }
285        }
286      }
287      change_level_to(s,number_of_nodes);
288      //level.set(s,number_of_nodes);
289
290      /*
291      //Setting starting level values using reverse bfs
292      reverse_bfs<Graph> rev_bfs(G,t);
293      rev_bfs.run();
294      //write_property_vector(rev_bfs.dist,"rev_bfs");
295      for(NodeIt i=G.template first<NodeIt>(); G.valid(i); G.next(i)) {
296        change_level_to(i,rev_bfs.dist(i));
297        //level.put(i,rev_bfs.dist.get(i));
298      }
299      */
300      //------------------------------------
301      //This is the only part that uses BFS
302      //------------------------------------
303
304
305      //Starting level of s
306      change_level_to(s,number_of_nodes);
307      //level.put(s,number_of_nodes);
308
309
310      //we push as much preflow from s as possible to start with
311      for(OutEdgeIt j=G.template first<OutEdgeIt>(s); G.valid(j); G.next(j)){
312        modify_preflow(j,capacity[j] );
313        make_active(G.target(j));
314        int lev=level[G.target(j)];
315        if(highest_active<lev){
316          highest_active=lev;
317        }
318      }
319      //cout<<highest_active<<endl;
320    }
321
322
323    //If the preflow is less than the capacity on the given edge
324    //then it is an edge in the residual graph
325    bool is_admissible_forward_edge(Edge j, int& new_level){
326
327      if (capacity[j]>preflow[j]){
328        if(level[G.source(j)]==level[G.target(j)]+1){
329          return true;
330        }
331        else{
332          if (level[G.target(j)] < new_level)
333            new_level=level[G.target(j)];
334        }
335      }
336      return false;
337    }
338
339    //If the preflow is greater than 0 on the given edge
340    //then the edge reversd is an edge in the residual graph
341    bool is_admissible_backward_edge(Edge j, int& new_level){
342
343      if (0<preflow[j]){
344        if(level[G.source(j)]==level[G.target(j)]-1){
345
346          return true;
347        }
348        else{
349          if (level[G.source(j)] < new_level)
350            new_level=level[G.source(j)];
351        }
352
353      }
354      return false;
355    }
356
357
358  };  //class preflow_push
359
360  template<typename Graph, typename T>
361    T preflow_push<Graph, T>::run() {
362
363    preprocess();
364    //write_property_vector(level,"level");
365    T e,v;
366    Node a;
367    while (a=get_active_node(), G.valid(a)){
368
369      //cout<<G.id(a)<<endl;
370      //write_property_vector(excess,"excess");
371      //write_property_vector(level,"level");
372
373
374      bool go_to_next_node=false;
375      e = excess[a];
376      while (!go_to_next_node){
377        //Initial value for the new level for the active node we are dealing with
378        int new_level=2*number_of_nodes;
379        //write_property_vector(excess,"excess");
380        //write_property_vector(level,"level");
381        //cout<<G.id(a)<<endl;
382        //Out edges from node a
383        {
384          OutEdgeIt j=G.template first<OutEdgeIt>(a);
385          while (G.valid(j) && e){
386
388              v=min(e,capacity[j] - preflow[j]);
389              e -= v;
390              //New node might become active
391              if (excess[G.target(j)]==0){
392                make_active(G.target(j));
393              }
394              modify_preflow(j,v);
395            }
396            G.next(j);
397          }
398        }
399        //In edges to node a
400        {
401          InEdgeIt j=G.template first<InEdgeIt>(a);
402          while (G.valid(j) && e){
404              v=min(e,preflow[j]);
405              e -= v;
406              //New node might become active
407              if (excess[G.source(j)]==0){
408                make_active(G.source(j));
409              }
410              modify_preflow(j,-v);
411            }
412            G.next(j);
413          }
414        }
415
416        //if (G.id(a)==999)
417        //cout<<new_level<<" e: "<<e<<endl;
418        //cout<<G.id(a)<<" "<<new_level<<endl;
419
420        if (0==e){
421          //Saturating push
422          go_to_next_node=true;
423        }
424        else{//If there is still excess in node a
425
426          //change_level_to(a,new_level+1);
427
428          //Level remains empty
429          if (num_of_nodes_on_level[level[a]]==1){
430            change_level_to(a,number_of_nodes);
431            //go_to_next_node=True;
432          }
433          else{
434            change_level_to(a,new_level+1);
435            //increase_level(a);
436          }
437
438
439
440
441          switch(node_examination){
442          case examine_to_relabel:
443            make_active(a);
444
445            go_to_next_node = true;
446            break;
447          default:
448            break;
449          }
450
451
452
453        }//if (0==e)
454      }
455    }
456    maxflow_value = excess[t];
457    return maxflow_value;
458  }//run
459
460
461}//namespace lemon
462
463#endif //PREFLOW_PUSH_HH
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