operations_research::GreedySolutionGenerator Class Reference

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

Detailed Description

The consistency level is maintained up to kFreeAndUncovered.

The first solution is obtained using the Chvatal heuristic, that guarantees that the solution is at most 1 + log(n) times the optimal value. Vasek Chvatal, 1979. A greedy heuristic for the set-covering problem. Mathematics of Operations Research, 4(3):233-235, 1979. http://www.jstor.org/stable/3689577

Chvatal's heuristic works as follows: Choose the subset that covers as many remaining uncovered elements as possible for the least possible cost per element and iterate.

The following papers dive into the details of this class of algorithms.

Young, Neal E. 2008. “Greedy Set-Cover Algorithms.” In Encyclopedia of Algorithms, 379–81. Boston, MA: Springer US. Draft at: http://www.cs.ucr.edu/~neal/non_arxiv/Young08SetCover.pdf

Cormode, Graham, Howard Karloff, and Anthony Wirth. 2010. “Set Cover Algorithms for Very Large Datasets.” In CIKM ’10. ACM Press. https://doi.org/10.1145/1871437.1871501.

Definition at line 301 of file set_cover_heuristics.h.

#include <set_cover_heuristics.h>

Inheritance diagram for operations_research::GreedySolutionGenerator:

Public Member Functions
	GreedySolutionGenerator (SetCoverInvariant *inv)
	GreedySolutionGenerator (SetCoverInvariant *inv, absl::string_view name)
bool	NextSolution (absl::Span< const SubsetIndex > focus) final
	GreedySolutionGenerator.
bool	NextSolution () final
	Virtual methods that must be implemented by derived classes.
bool	NextSolution (const SubsetBoolVector &in_focus) final
	Same as above, but with a vector of Booleans as focus.
Public Member Functions inherited from operations_research::SubsetListBasedSolutionGenerator
	SubsetListBasedSolutionGenerator (SetCoverInvariant *inv, SetCoverInvariant::ConsistencyLevel consistency_level, absl::string_view class_name, absl::string_view name)
bool	NextSolution (absl::Span< const SubsetIndex > _) override
bool	NextSolution () final
	Virtual methods that must be implemented by derived classes.
bool	NextSolution (const SubsetBoolVector &in_focus) final
	Same as above, but with a vector of Booleans as focus.
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

GreedySolutionGenerator() [1/2]

operations_research::GreedySolutionGenerator::GreedySolutionGenerator ( SetCoverInvariant * inv )

inlineexplicit

Definition at line 303 of file set_cover_heuristics.h.

GreedySolutionGenerator() [2/2]

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

inline

Definition at line 306 of file set_cover_heuristics.h.

Member Function Documentation

NextSolution() [1/3]

bool operations_research::SubsetListBasedSolutionGenerator::NextSolution ( )

inlinefinalvirtual

Virtual methods that must be implemented by derived classes.

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

Implements operations_research::SetCoverSolutionGenerator.

Definition at line 181 of file set_cover_heuristics.h.

NextSolution() [2/3]

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

finalvirtual

GreedySolutionGenerator.

NOMUTANTS – reason, for C++

The priority queue maintains the maximum number of elements covered by unit of cost. We chose 16 as the arity of the heap after some testing.

Todo

(user): research more about the best value for Arity.

NOMUTANTS – reason, for C++

Don't expect pq to be empty, because of the break in the while loop.

Implements operations_research::SetCoverSolutionGenerator.

Definition at line 85 of file set_cover_heuristics.cc.

NextSolution() [3/3]

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

inlinefinalvirtual

Same as above, but with a vector of Booleans as focus.

Implements operations_research::SetCoverSolutionGenerator.

Definition at line 183 of file set_cover_heuristics.h.

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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