CapacityScaling< GR, V, C, TR > Class Template Reference

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Detailed Description

template<typename GR, typename V, typename C, typename TR>
class lemon::CapacityScaling< GR, V, C, TR >

CapacityScaling implements the capacity scaling version of the successive shortest path algorithm for finding a minimum cost flow [AMO93], [EK72]. It is an efficient dual solution method.

Most of the parameters of the problem (except for the digraph) can be given using separate functions, and the algorithm can be executed using the run() function. If some parameters are not specified, then default values will be used.

Template Parameters:

GR	The digraph type the algorithm runs on.
V	The number type used for flow amounts, capacity bounds and supply values in the algorithm. By default, it is int.
C	The number type used for costs and potentials in the algorithm. By default, it is the same as V.
TR	The traits class that defines various types used by the algorithm. By default, it is CapacityScalingDefaultTraits<GR, V, C>. In most cases, this parameter should not be set directly, consider to use the named template parameters instead.

Warning:

Both number types must be signed and all input data must be integer.

This algorithm does not support negative costs for such arcs that have infinite upper bound.

#include <lemon/capacity_scaling.h>

List of all members.

Classes
struct	SetHeap
	Named parameter for setting Heap type. More...
Public Types
enum	ProblemType { INFEASIBLE, OPTIMAL, UNBOUNDED }
	Problem type constants for the run() function. More...
typedef TR::Digraph	Digraph
	The type of the digraph.
typedef TR::Value	Value
	The type of the flow amounts, capacity bounds and supply values.
typedef TR::Cost	Cost
	The type of the arc costs.
typedef TR::Heap	Heap
	The type of the heap used for internal Dijkstra computations.
typedef TR	Traits
	The traits class of the algorithm.
Public Member Functions
	CapacityScaling (const GR &graph)
	Constructor.
Parameters
The parameters of the algorithm can be specified using these functions.
template<typename LowerMap >
CapacityScaling &	lowerMap (const LowerMap &map)
	Set the lower bounds on the arcs.
template<typename UpperMap >
CapacityScaling &	upperMap (const UpperMap &map)
	Set the upper bounds (capacities) on the arcs.
template<typename CostMap >
CapacityScaling &	costMap (const CostMap &map)
	Set the costs of the arcs.
template<typename SupplyMap >
CapacityScaling &	supplyMap (const SupplyMap &map)
	Set the supply values of the nodes.
CapacityScaling &	stSupply (const Node &s, const Node &t, Value k)
	Set single source and target nodes and a supply value.
Execution control
The algorithm can be executed using run().
ProblemType	run (int factor=4)
	Run the algorithm.
CapacityScaling &	resetParams ()
	Reset all the parameters that have been given before.
CapacityScaling &	reset ()
	Reset the internal data structures and all the parameters that have been given before.
Query Functions
The results of the algorithm can be obtained using these functions. The run() function must be called before using them.
template<typename Number >
Number	totalCost () const
	Return the total cost of the found flow.
Value	flow (const Arc &a) const
	Return the flow on the given arc.
template<typename FlowMap >
void	flowMap (FlowMap &map) const
	Return the flow map (the primal solution).
Cost	potential (const Node &n) const
	Return the potential (dual value) of the given node.
template<typename PotentialMap >
void	potentialMap (PotentialMap &map) const
	Return the potential map (the dual solution).
Public Attributes
const Value	INF
	Constant for infinite upper bounds (capacities).

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Member Enumeration Documentation

enum ProblemType

Enum type containing the problem type constants that can be returned by the run() function of the algorithm.

Enumerator:

INFEASIBLE	The problem has no feasible solution (flow).
OPTIMAL	The problem has optimal solution (i.e. it is feasible and bounded), and the algorithm has found optimal flow and node potentials (primal and dual solutions).
UNBOUNDED	The digraph contains an arc of negative cost and infinite upper bound. It means that the objective function is unbounded on that arc, however, note that it could actually be bounded over the feasible flows, but this algroithm cannot handle these cases.

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Constructor & Destructor Documentation

CapacityScaling

(

const GR &

graph

)

[inline]

The constructor of the class.

Parameters:

graph

The digraph the algorithm runs on.

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Member Function Documentation

CapacityScaling& lowerMap

(

const LowerMap &

map

)

[inline]

This function sets the lower bounds on the arcs. If it is not used before calling run(), the lower bounds will be set to zero on all arcs.

Parameters:

map	An arc map storing the lower bounds. Its Value type must be convertible to the Value type of the algorithm.

Returns:

(*this)

CapacityScaling& upperMap

(

const UpperMap &

map

)

[inline]

This function sets the upper bounds (capacities) on the arcs. If it is not used before calling run(), the upper bounds will be set to INF on all arcs (i.e. the flow value will be unbounded from above).

Parameters:

map	An arc map storing the upper bounds. Its Value type must be convertible to the Value type of the algorithm.

Returns:

(*this)

CapacityScaling& costMap

(

const CostMap &

map

)

[inline]

This function sets the costs of the arcs. If it is not used before calling run(), the costs will be set to 1 on all arcs.

Parameters:

map	An arc map storing the costs. Its Value type must be convertible to the Cost type of the algorithm.

Returns:

(*this)

CapacityScaling& supplyMap

(

const SupplyMap &

map

)

[inline]

This function sets the supply values of the nodes. If neither this function nor stSupply() is used before calling run(), the supply of each node will be set to zero.

Parameters:

map	A node map storing the supply values. Its Value type must be convertible to the Value type of the algorithm.

Returns:

(*this)

CapacityScaling& stSupply	(	const Node &	s,
		const Node &	t,
		Value	k
	)		[inline]

This function sets a single source node and a single target node and the required flow value. If neither this function nor supplyMap() is used before calling run(), the supply of each node will be set to zero.

Using this function has the same effect as using supplyMap() with such a map in which k is assigned to s, -k is assigned to t and all other nodes have zero supply value.

Parameters:

s	The source node.
t	The target node.
k	The required amount of flow from node s to node t (i.e. the supply of s and the demand of t).

Returns:

(*this)

ProblemType run

(

int

factor = 4

)

[inline]

This function runs the algorithm. The paramters can be specified using functions lowerMap(), upperMap(), costMap(), supplyMap(), stSupply(). For example,

   CapacityScaling<ListDigraph> cs(graph);
   cs.lowerMap(lower).upperMap(upper).costMap(cost)
     .supplyMap(sup).run();

This function can be called more than once. All the given parameters are kept for the next call, unless resetParams() or reset() is used, thus only the modified parameters have to be set again. If the underlying digraph was also modified after the construction of the class (or the last reset() call), then the reset() function must be called.

Parameters:

factor

The capacity scaling factor. It must be larger than one to use scaling. If it is less or equal to one, then scaling will be disabled.

Returns:

INFEASIBLE if no feasible flow exists,
OPTIMAL if the problem has optimal solution (i.e. it is feasible and bounded), and the algorithm has found optimal flow and node potentials (primal and dual solutions),
UNBOUNDED if the digraph contains an arc of negative cost and infinite upper bound. It means that the objective function is unbounded on that arc, however, note that it could actually be bounded over the feasible flows, but this algroithm cannot handle these cases.

See also:

ProblemType

resetParams(), reset()

CapacityScaling& resetParams

(

)

[inline]

This function resets all the paramaters that have been given before using functions lowerMap(), upperMap(), costMap(), supplyMap(), stSupply().

It is useful for multiple run() calls. Basically, all the given parameters are kept for the next run() call, unless resetParams() or reset() is used. If the underlying digraph was also modified after the construction of the class or the last reset() call, then the reset() function must be used, otherwise resetParams() is sufficient.

For example,

   CapacityScaling<ListDigraph> cs(graph);

   // First run
   cs.lowerMap(lower).upperMap(upper).costMap(cost)
     .supplyMap(sup).run();

   // Run again with modified cost map (resetParams() is not called,
   // so only the cost map have to be set again)
   cost[e] += 100;
   cs.costMap(cost).run();

   // Run again from scratch using resetParams()
   // (the lower bounds will be set to zero on all arcs)
   cs.resetParams();
   cs.upperMap(capacity).costMap(cost)
     .supplyMap(sup).run();

Returns:

(*this)

See also:

reset(), run()

CapacityScaling& reset

(

)

[inline]

This function resets the internal data structures and all the paramaters that have been given before using functions lowerMap(), upperMap(), costMap(), supplyMap(), stSupply().

It is useful for multiple run() calls. Basically, all the given parameters are kept for the next run() call, unless resetParams() or reset() is used. If the underlying digraph was also modified after the construction of the class or the last reset() call, then the reset() function must be used, otherwise resetParams() is sufficient.

See resetParams() for examples.

Returns:

(*this)

See also:

resetParams(), run()

Number totalCost

(

)

const [inline]

This function returns the total cost of the found flow. Its complexity is O(e).

Note:

The return type of the function can be specified as a template parameter. For example,

   cs.totalCost<double>();

It is useful if the total cost cannot be stored in the Cost type of the algorithm, which is the default return type of the function.

Precondition:

run() must be called before using this function.

Value flow

(

const Arc &

a

)

const [inline]

This function returns the flow on the given arc.

Precondition:

run() must be called before using this function.

void flowMap

(

FlowMap &

map

)

const [inline]

This function copies the flow value on each arc into the given map. The Value type of the algorithm must be convertible to the Value type of the map.

Precondition:

run() must be called before using this function.

Cost potential

(

const Node &

n

)

const [inline]

This function returns the potential (dual value) of the given node.

Precondition:

run() must be called before using this function.

void potentialMap

(

PotentialMap &

map

)

const [inline]

This function copies the potential (dual value) of each node into the given map. The Cost type of the algorithm must be convertible to the Value type of the map.

Precondition:

run() must be called before using this function.

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Member Data Documentation

const Value INF

Constant for infinite upper bounds (capacities). It is std::numeric_limits<Value>::infinity() if available, std::numeric_limits<Value>::max() otherwise.