maxflow_ff.cpp

/* This software is distributed under the GNU Lesser General Public License */
//==========================================================================
//
//   maxflow_ff.cpp 
//
//==========================================================================
// $Id: maxflow_ff.cpp,v 1.7 2001/11/07 13:58:10 pick Exp $

#include <GTL/maxflow_ff.h>

#include <cstdlib>
#include <iostream>
#include <cassert>

__GTL_BEGIN_NAMESPACE

maxflow_ff::maxflow_ff()
{
    max_graph_flow = 0.0;
    set_vars_executed = false;
}


maxflow_ff::~maxflow_ff()
{
}


void maxflow_ff::set_vars(const edge_map<double>& edge_capacity)
{
    this->edge_capacity = edge_capacity;
    artif_source_target = true;
    max_graph_flow = 0.0;
    set_vars_executed = true;
}


void maxflow_ff::set_vars(const edge_map<double>& edge_capacity, 
    const node& net_source, const node& net_target)
{
    this->edge_capacity = edge_capacity;
    this->net_source = net_source;
    this->net_target = net_target;
    artif_source_target = false;
    max_graph_flow = 0.0;
    set_vars_executed = true;
}


int maxflow_ff::check(graph& G)
{
    if (!set_vars_executed)
    {
	return(GTL_ERROR);
    }
    graph::edge_iterator edge_it = G.edges_begin();
    graph::edge_iterator edges_end = G.edges_end();
    while (edge_it != edges_end)
    {
	if (edge_capacity[*edge_it] < 0)
	{
	    return(GTL_ERROR);
	}
	++edge_it;
    }
    // G.is_acyclic may be false
    if ((G.number_of_nodes() <= 1) || (!G.is_connected()) || (G.is_undirected()))
    {
	return(GTL_ERROR);
    }
    if (artif_source_target)
    {
	bool source_found = false;
	bool target_found = false;
	graph::node_iterator node_it = G.nodes_begin();
	graph::node_iterator nodes_end = G.nodes_end();
	while (node_it != nodes_end)
	{
	    if (node_it->indeg() == 0)
	    {
		source_found = true;
	    }
	    if (node_it->outdeg() == 0)
	    {
		target_found = true;
	    }
	    ++node_it;
	}
	if (!(source_found && target_found))
	{
	    return(GTL_ERROR);
	}
    }
    else
    {
	if (net_source == net_target)
	{
	    return(GTL_ERROR);
	}
    }
    return(GTL_OK);	// ok
}


int maxflow_ff::run(graph& G)
{
    // init
    if (artif_source_target)
    {
	create_artif_source_target(G);
    }
    prepare_run(G);

    node_map<edge> last_edge(G);

    while (get_sp(G, last_edge) == SP_FOUND)
    {
	comp_single_flow(G, last_edge);
    }

    restore_graph(G);
    return(GTL_OK);
}


double maxflow_ff::get_max_flow(const edge& e) const
{
    return(edge_max_flow[e]);
}


double maxflow_ff::get_max_flow() const
{
    return(max_graph_flow);
}


double maxflow_ff::get_rem_cap(const edge& e) const
{
    return(edge_capacity[e] - edge_max_flow[e]);
}


void maxflow_ff::reset()
{
}


void maxflow_ff::create_artif_source_target(graph& G)
{
    net_source = G.new_node();
    net_target = G.new_node();
    edge e;
    graph::node_iterator node_it = G.nodes_begin();
    graph::node_iterator nodes_end = G.nodes_end();
    while (node_it != nodes_end)
    {
	if (*node_it != net_source && node_it->indeg() == 0)
	{
	    e = G.new_edge(net_source, *node_it);
	    edge_capacity[e] = 1.0;	// 1.0 prevents e from hiding
	    node::out_edges_iterator out_edge_it = node_it->out_edges_begin();
	    node::out_edges_iterator out_edges_end = node_it->out_edges_end();
	    while (out_edge_it != out_edges_end)
	    {
		edge_capacity[e] += edge_capacity[*out_edge_it];
		++out_edge_it;
	    }
	}
	if (*node_it != net_target && node_it->outdeg() == 0)
	{
	    e = G.new_edge(*node_it, net_target);
	    edge_capacity[e] = 1.0;	// 1.0 prevents e from hiding
	    node::in_edges_iterator in_edge_it = node_it->in_edges_begin();
	    node::in_edges_iterator in_edges_end = node_it->in_edges_end();
	    while (in_edge_it != in_edges_end)
	    {
		edge_capacity[e] += edge_capacity[*in_edge_it];
		++in_edge_it;
	    }
	}
	++node_it;
    }
}


void maxflow_ff::prepare_run(const graph& G)
{
    edge_max_flow.init(G, 0.0);
    edge_org.init(G, true);
    back_edge_exists.init(G, false);
    max_graph_flow = 0.0;
}


void maxflow_ff::comp_single_flow(graph& G, node_map<edge>& last_edge)
{
    double min_value = extra_charge(last_edge);

    node cur_node = net_target;
    do
    {
	if (edge_org[last_edge[cur_node]])	// shortest path runs over a org. edge
	{
	    if (!back_edge_exists[last_edge[cur_node]])	// create back edge
	    {
		create_back_edge(G, last_edge[cur_node]);
	    }
	    edge_max_flow[last_edge[cur_node]] += min_value;
	    G.restore_edge(back_edge[last_edge[cur_node]]);
	    edge_capacity[back_edge[last_edge[cur_node]]] += min_value;
	}
	else	// shortest path runs over a inserted back edge
	{
	    edge oe = back_edge[last_edge[cur_node]];
	    G.restore_edge(oe);
	    edge_max_flow[oe] -= min_value;
	    edge_capacity[last_edge[cur_node]] -= min_value;
	}
	if (edge_capacity[last_edge[cur_node]] <= edge_max_flow[last_edge[cur_node]])
	{
	    G.hide_edge(last_edge[cur_node]);
	}
	cur_node = last_edge[cur_node].source();
    }
    while (cur_node != net_source);
}


int maxflow_ff::get_sp(const graph& G, node_map<edge>& last_edge)
{
	std::queue<node> next_nodes;
    node_map<bool> visited(G, false);
    next_nodes.push(net_source);
    visited[net_source] = true;

    if (comp_sp(G, next_nodes, visited, last_edge) == SP_FOUND)
    {
	return(SP_FOUND);
    }
    else
    {
	return(NO_SP_FOUND);
    }
}


int maxflow_ff::comp_sp(const graph& /*G*/, std::queue<node>& next_nodes,
    node_map<bool>& visited, node_map<edge>& last_edge)
{
    node cur_node;

    while (!next_nodes.empty())
    {
	cur_node = next_nodes.front();
	next_nodes.pop();
		
	node::out_edges_iterator out_edge_it = cur_node.out_edges_begin();
	node::out_edges_iterator out_edges_end = cur_node.out_edges_end();
	while (out_edge_it != out_edges_end)
	{
	    node next = out_edge_it->target();
	    if (!visited[next])
	    {
		last_edge[next] = *out_edge_it;
		if (next == net_target)
		{
		    return(SP_FOUND);
		}
		else
		{
		    next_nodes.push(next);
		    visited[next] = true;
		}
	    }
	    ++out_edge_it;
	}
    }
    return(NO_SP_FOUND);
}


double maxflow_ff::extra_charge(const node_map<edge>& last_edge) const
{
    node cur_node = net_target;
    double min_value = 
	edge_capacity[last_edge[cur_node]] - edge_max_flow[last_edge[cur_node]];
    double cur_capacity;

    do
    {
	cur_capacity = 
	    edge_capacity[last_edge[cur_node]] - edge_max_flow[last_edge[cur_node]];

	if (cur_capacity < min_value) min_value = cur_capacity;
	cur_node = last_edge[cur_node].source();
    }
    while (cur_node != net_source);
    return(min_value);
}


void maxflow_ff::create_back_edge(graph& G, const edge& org_edge)
{
    edge be = G.new_edge(org_edge.target(), org_edge.source());
    edge_org[be] = false;
    edges_not_org.push_back(be);
    back_edge[org_edge] = be;
    back_edge[be] = org_edge;
    edge_max_flow[be] = 0.0;
    edge_capacity[be] = 0.0;
    back_edge_exists[org_edge] = true;
    back_edge_exists[be] = true;	// a back edge always has a org. edge ;-)
}


void maxflow_ff::comp_max_flow(const graph& /*G*/)
{
    max_graph_flow = 0.0;

    node::out_edges_iterator out_edge_it = net_source.out_edges_begin();
    node::out_edges_iterator out_edges_end = net_source.out_edges_end();
    while (out_edge_it != out_edges_end)
    {
	max_graph_flow += edge_max_flow[*out_edge_it];
	++out_edge_it;
    }
}


void maxflow_ff::restore_graph(graph& G)
{
    G.restore_graph();	// hidden edges can not be deleted!
    while (!edges_not_org.empty())
    {
	G.del_edge(edges_not_org.front());
	edges_not_org.pop_front();
    }
    comp_max_flow(G);
    if (artif_source_target)
    {
	G.del_node(net_source);
	G.del_node(net_target);
    }
}

__GTL_END_NAMESPACE

//--------------------------------------------------------------------------
//   end of file
//--------------------------------------------------------------------------