operations_research::ElementDegreeSolutionGenerator Class Reference

The consistency level is maintained up to kFreeAndUncovered. More...

Detailed Description

The consistency level is maintained up to kFreeAndUncovered.

Solution generator based on the degree of elements. The degree of an element is the number of subsets covering it. The generator consists in iteratively choosing a non-covered element with the smallest degree, and selecting a subset that covers it with the least ratio cost / number of uncovered elements. The number of uncovered elements are updated for each impacted subset. The newly-covered elements degrees are also updated and set to zero.

Definition at line 324 of file set_cover_heuristics.h.

#include <set_cover_heuristics.h>

Inheritance diagram for operations_research::ElementDegreeSolutionGenerator:

Public Member Functions
	ElementDegreeSolutionGenerator (SetCoverInvariant *inv)
	ElementDegreeSolutionGenerator (SetCoverInvariant *inv, absl::string_view name)
bool	NextSolution (const SubsetBoolVector &in_focus) final
bool	NextSolution (absl::Span< const SubsetIndex > focus) final
bool	NextSolution () final
	Virtual methods that must be implemented by derived classes.
Public Member Functions inherited from operations_research::BoolVectorBasedSolutionGenerator
	BoolVectorBasedSolutionGenerator (SetCoverInvariant *inv, SetCoverInvariant::ConsistencyLevel consistency_level, absl::string_view class_name, absl::string_view name)
Public Member Functions inherited from operations_research::SetCoverSolutionGenerator
	SetCoverSolutionGenerator (SetCoverInvariant *inv, SetCoverInvariant::ConsistencyLevel consistency_level, absl::string_view class_name, absl::string_view name)
virtual	~SetCoverSolutionGenerator ()=default
void	SetName (const absl::string_view name)
SetCoverInvariant *	inv () const
virtual SetCoverSolutionGenerator &	ResetLimits ()
	Resets the limits to their default values.
SetCoverSolutionGenerator &	SetMaxIterations (int64_t max_iterations)
	Sets the maximum number of iterations.
int64_t	max_iterations () const
	Returns the maximum number of iterations.
SetCoverSolutionGenerator &	SetTimeLimitInSeconds (double seconds)
	Sets the time limit in seconds.
absl::Duration	run_time () const
double	run_time_in_seconds () const
	Returns the total elapsed runtime in seconds.
double	run_time_in_microseconds () const
	Returns the total elapsed runtime in microseconds.
std::string	name () const
	Returns the name of the heuristic.
std::string	class_name () const
	Returns the name of the class.
Cost	cost () const
	Returns the current cost of the solution in the invariant.
bool	CheckInvariantConsistency () const

Additional Inherited Members
Protected Member Functions inherited from operations_research::SetCoverSolutionGenerator
SetCoverModel *	model () const
	Accessors.
BaseInt	num_subsets () const
double	time_limit_in_seconds () const
	The time limit in seconds.
Protected Attributes inherited from operations_research::SetCoverSolutionGenerator
absl::Duration	run_time_
	run_time_ is an abstract duration for the time spent in NextSolution().
SetCoverInvariant::ConsistencyLevel	consistency_level_
	The consistency needed by the solution generator.

Constructor & Destructor Documentation

ElementDegreeSolutionGenerator() [1/2]

operations_research::ElementDegreeSolutionGenerator::ElementDegreeSolutionGenerator ( SetCoverInvariant * inv )

inlineexplicit

Definition at line 326 of file set_cover_heuristics.h.

ElementDegreeSolutionGenerator() [2/2]

operations_research::ElementDegreeSolutionGenerator::ElementDegreeSolutionGenerator ( SetCoverInvariant * inv, absl::string_view name )

inline

Definition at line 329 of file set_cover_heuristics.h.

Member Function Documentation

NextSolution() [1/3]

bool operations_research::BoolVectorBasedSolutionGenerator::NextSolution ( )

inlinefinalvirtual

Virtual methods that must be implemented by derived classes.

Computes the next full solution taking into account all the subsets.

Reimplemented from operations_research::BoolVectorBasedSolutionGenerator.

Definition at line 222 of file set_cover_heuristics.h.

NextSolution() [2/3]

bool operations_research::BoolVectorBasedSolutionGenerator::NextSolution ( absl::Span< const SubsetIndex > focus )

inlinefinalvirtual

Computes the next partial solution considering only the subsets whose indices are in focus.

Reimplemented from operations_research::BoolVectorBasedSolutionGenerator.

Definition at line 218 of file set_cover_heuristics.h.

NextSolution() [3/3]

bool operations_research::ElementDegreeSolutionGenerator::NextSolution ( const SubsetBoolVector & in_focus )

finalvirtual

ElementDegreeSolutionGenerator. There is no need to use a priority queue here, as the ratios are computed on-demand. Also elements are sorted based on degree once and for all and moved past when the elements become already covered.

Create the list of all the indices in the problem.

No need to cover an element that is already covered.

Compare R = costs[subset] / num_free_elements with B = best_subset_cost / best_subset_num_free_elts. If R < B, we choose subset. If the ratios are the same, we choose the subset with the most free elements.

Todo

(user): What about adding a tolerance for equality, which could further favor larger columns?

Reimplemented from operations_research::BoolVectorBasedSolutionGenerator.

Definition at line 366 of file set_cover_heuristics.cc.

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The documentation for this class was generated from the following files:

• ortools/set_cover/set_cover_heuristics.h
• ortools/set_cover/set_cover_heuristics.cc