[Lemon-commits] [lemon_svn] jacint: r34 - hugo/trunk/src/work
Lemon SVN
svn at lemon.cs.elte.hu
Mon Nov 6 20:36:56 CET 2006
Author: jacint
Date: Tue Jan 20 22:27:10 2004
New Revision: 34
Added:
hugo/trunk/src/work/preflow_push_max_flow.hh
Log:
A max flow algorithm counting only the max flow value
Added: hugo/trunk/src/work/preflow_push_max_flow.hh
==============================================================================
--- (empty file)
+++ hugo/trunk/src/work/preflow_push_max_flow.hh Tue Jan 20 22:27:10 2004
@@ -0,0 +1,315 @@
+/*
+preflow_push_max_flow_hh
+by jacint.
+Runs a preflow push algorithm with the modification,
+that we do not push on nodes with level at least n.
+Moreover, if a level gets empty, we put all nodes above that
+level to level n. Hence, in the end, we arrive at a maximum preflow
+with value of a max flow value. An empty level gives a minimum cut.
+
+Member functions:
+
+void run() : runs the algorithm
+
+ The following functions should be used after run() was already run.
+
+T maxflow() : returns the value of a maximum flow
+
+node_property_vector<graph_type, bool> mincut(): returns a
+ characteristic vector of a minimum cut.
+*/
+
+#ifndef PREFLOW_PUSH_MAX_FLOW_HH
+#define PREFLOW_PUSH_MAX_FLOW_HH
+
+#include <algorithm>
+#include <vector>
+#include <stack>
+
+#include <marci_list_graph.hh>
+#include <marci_graph_traits.hh>
+#include <marci_property_vector.hh>
+#include <reverse_bfs.hh>
+
+
+namespace marci {
+
+ template <typename graph_type, typename T>
+ class preflow_push_max_flow {
+
+ typedef typename graph_traits<graph_type>::node_iterator node_iterator;
+ typedef typename graph_traits<graph_type>::each_node_iterator each_node_iterator;
+ typedef typename graph_traits<graph_type>::out_edge_iterator out_edge_iterator;
+ typedef typename graph_traits<graph_type>::in_edge_iterator in_edge_iterator;
+
+ graph_type& G;
+ node_iterator s;
+ node_iterator t;
+ edge_property_vector<graph_type, T>& capacity;
+ T value;
+ node_property_vector<graph_type, bool> mincutvector;
+
+
+
+ public:
+
+ preflow_push_max_flow(graph_type& _G, node_iterator _s, node_iterator _t, edge_property_vector<graph_type, T>& _capacity) : G(_G), s(_s), t(_t), capacity(_capacity), mincutvector(_G, false) { }
+
+
+ /*
+ The run() function runs a modified version of the highest label preflow-push, which only
+ finds a maximum preflow, hence giving the value of a maximum flow.
+ */
+ void run() {
+
+ edge_property_vector<graph_type, T> flow(G, 0); //the flow value, 0 everywhere
+ node_property_vector<graph_type, int> level(G); //level of node
+ node_property_vector<graph_type, T> excess(G); //excess of node
+
+ int n=number_of(G.first_node()); //number of nodes
+ int b=n-2;
+ /*b is a bound on the highest level of an active node. In the beginning it is at most n-2.*/
+
+ std::vector<int> numb(n); //The number of nodes on level i < n.
+
+ std::vector<std::stack<node_iterator> > stack(2*n-1); //Stack of the active nodes in level i.
+
+
+
+ /*Reverse_bfs from t, to find the starting level.*/
+
+ reverse_bfs<list_graph> bfs(G, t);
+ bfs.run();
+ for(each_node_iterator v=G.first_node(); v.is_valid(); ++v)
+ {
+ int dist=bfs.dist(v);
+ level.put(v, dist);
+ ++numb[dist];
+ }
+
+ /*The level of s is fixed to n*/
+ level.put(s,n);
+
+
+ /* Starting flow. It is everywhere 0 at the moment. */
+
+ for(out_edge_iterator i=G.first_out_edge(s); i.is_valid(); ++i)
+ {
+ node_iterator w=G.head(i);
+ flow.put(i, capacity.get(i));
+ stack[bfs.dist(w)].push(w);
+ excess.put(w, capacity.get(i));
+ }
+
+
+ /*
+ End of preprocessing
+ */
+
+
+
+
+ /*
+ Push/relabel on the highest level active nodes.
+ */
+
+ /*While there exists an active node.*/
+ while (b) {
+
+ /*We decrease the bound if there is no active node of level b.*/
+ if (stack[b].empty()) {
+ --b;
+ } else {
+
+ node_iterator w=stack[b].top(); //w is the highest label active node.
+ stack[b].pop(); //We delete w from the stack.
+
+ int newlevel=2*n-2; //In newlevel we maintain the next level of w.
+
+ for(out_edge_iterator e=G.first_out_edge(w); e.is_valid(); ++e) {
+ node_iterator v=G.head(e);
+ /*e is the edge wv.*/
+
+ if (flow.get(e)<capacity.get(e)) {
+ /*e is an edge of the residual graph */
+
+ if(level.get(w)==level.get(v)+1) {
+ /*Push is allowed now*/
+
+ if (capacity.get(e)-flow.get(e) > excess.get(w)) {
+ /*A nonsaturating push.*/
+
+ if (excess.get(v)==0 && v != s) stack[level.get(v)].push(v);
+ /*v becomes active.*/
+
+ flow.put(e, flow.get(e)+excess.get(w));
+ excess.put(v, excess.get(v)+excess.get(w));
+ excess.put(w,0);
+ //std::cout << w << " " << v <<" elore elen nonsat pump " << std::endl;
+ break;
+ } else {
+ /*A saturating push.*/
+
+ if (excess.get(v)==0 && v != s) stack[level.get(v)].push(v);
+ /*v becomes active.*/
+
+ excess.put(v, excess.get(v)+capacity.get(e)-flow.get(e));
+ excess.put(w, excess.get(w)-capacity.get(e)+flow.get(e));
+ flow.put(e, capacity.get(e));
+ //std::cout << w <<" " << v <<" elore elen sat pump " << std::endl;
+ if (excess.get(w)==0) break;
+ /*If w is not active any more, then we go on to the next node.*/
+
+ } // if (capacity.get(e)-flow.get(e) > excess.get(w))
+ } // if (level.get(w)==level.get(v)+1)
+
+ else {newlevel = newlevel < level.get(v) ? newlevel : level.get(v);}
+
+ } //if (flow.get(e)<capacity.get(e))
+
+ } //for(out_edge_iterator e=G.first_out_edge(w); e.is_valid(); ++e)
+
+
+
+ for(in_edge_iterator e=G.first_in_edge(w); e.is_valid(); ++e) {
+ node_iterator v=G.tail(e);
+ /*e is the edge vw.*/
+
+ if (excess.get(w)==0) break;
+ /*It may happen, that w became inactive in the first 'for' cycle.*/
+
+ if(flow.get(e)>0) {
+ /*e is an edge of the residual graph */
+
+ if(level.get(w)==level.get(v)+1) {
+ /*Push is allowed now*/
+
+ if (flow.get(e) > excess.get(w)) {
+ /*A nonsaturating push.*/
+
+ if (excess.get(v)==0 && v != s) stack[level.get(v)].push(v);
+ /*v becomes active.*/
+
+ flow.put(e, flow.get(e)-excess.get(w));
+ excess.put(v, excess.get(v)+excess.get(w));
+ excess.put(w,0);
+ //std::cout << v << " " << w << " vissza elen nonsat pump " << std::endl;
+ break;
+ } else {
+ /*A saturating push.*/
+
+ if (excess.get(v)==0 && v != s) stack[level.get(v)].push(v);
+ /*v becomes active.*/
+
+ flow.put(e,0);
+ excess.put(v, excess.get(v)+flow.get(e));
+ excess.put(w, excess.get(w)-flow.get(e));
+ //std::cout << v <<" " << w << " vissza elen sat pump " << std::endl;
+ if (excess.get(w)==0) { break;}
+ } //if (flow.get(e) > excess.get(v))
+ } //if(level.get(w)==level.get(v)+1)
+
+ else {newlevel = newlevel < level.get(v) ? newlevel : level.get(v);}
+ //std::cout << "Leveldecrease of node " << w << " to " << newlevel << std::endl;
+
+ } //if (flow.get(e)>0)
+
+ } //for in-edge
+
+
+
+
+ /*
+ Relabel
+ */
+ if (excess.get(w)>0) {
+ /*Now newlevel <= n*/
+
+ int l=level.get(w); //l is the old level of w.
+ --numb[l];
+
+ if (newlevel == n) {
+ level.put(w,n);
+
+ } else {
+
+ if (numb[l]) {
+ /*If the level of w remains nonempty.*/
+
+ level.put(w,++newlevel);
+ ++numb[newlevel];
+ stack[newlevel].push(w);
+ b=newlevel;
+ } else {
+ /*If the level of w gets empty.*/
+
+ for (each_node_iterator v=G.first_node() ; v.is_valid() ; ++v) {
+ if (level.get(v) >= l ) {
+ level.put(v,n);
+ }
+ }
+
+ for (int i=l+1 ; i!=n ; ++i) numb[i]=0;
+ } //if (numb[l])
+
+ } // if (newlevel = n)
+
+ } // if (excess.get(w)>0)
+
+
+ } //else
+
+ } //while(b)
+
+ value=excess.get(t);
+ /*Max flow value.*/
+
+
+
+ /*
+ We find an empty level, e. The nodes above this level give
+ a minimum cut.
+ */
+
+ int e=1;
+
+ while(e) {
+ if(numb[e]) ++e;
+ else break;
+ }
+ for (each_node_iterator v=G.first_node(); v.is_valid(); ++v) {
+ if (level.get(v) > e) mincutvector.put(v, true);
+ }
+
+
+ } // void run()
+
+
+
+ /*
+ Returns the maximum value of a flow.
+ */
+
+ T maxflow() {
+ return value;
+ }
+
+
+
+ /*
+ Returns a minimum cut.
+ */
+
+ node_property_vector<graph_type, bool> mincut() {
+ return mincutvector;
+ }
+
+
+ };
+}//namespace marci
+#endif
+
+
+
+
+
More information about the Lemon-commits
mailing list