operations_research::LazySteepestSearch Class Reference

Detailed Description

Lazy Steepest Search is a variant of Steepest Search that does not use any priority queue to update the priorities of the subsets. The priorities are computed when needed. It is faster to compute because there are relatively few subsets in the solution, because the cardinality of the solution is bounded by the number of elements.

Definition at line 390 of file set_cover_heuristics.h.

#include <set_cover_heuristics.h>

Inheritance diagram for operations_research::LazySteepestSearch:

Public Member Functions
	LazySteepestSearch (SetCoverInvariant *inv)
	LazySteepestSearch (SetCoverInvariant *inv, absl::string_view name)
bool	NextSolution (const SubsetBoolVector &in_focus) final
	LazySteepestSearch.
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

LazySteepestSearch() [1/2]

operations_research::LazySteepestSearch::LazySteepestSearch ( SetCoverInvariant * inv )

inlineexplicit

Definition at line 392 of file set_cover_heuristics.h.

LazySteepestSearch() [2/2]

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

inline

Definition at line 395 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::LazySteepestSearch::NextSolution ( const SubsetBoolVector & in_focus )

finalvirtual

LazySteepestSearch.

First part of the trick: Since the heuristic is greedy, it only considers subsets that are selected and in_focus.

Todo

(user): use RadixSort with doubles and payloads.

Second part of the trick: ComputeIsRedundant is expensive, but it is going to be called only once per subset in the solution. Once this has been done, there is no need to update any priority queue, nor to use a stronger level of consistency than kCostAndCoverage. In the non-lazy version, the redundancy of a subset may be updated many times and the priority queue must be updated accordingly, including just for removing the subset that was just considered, A possible optimization would be to sort the elements by coverage and run ComputeIsRedundant with the new element order. This would make the subsets which cover only one element easier to prove non-redundant.

Reimplemented from operations_research::BoolVectorBasedSolutionGenerator.

Definition at line 529 of file set_cover_heuristics.cc.

---

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