Google OR-Tools v9.14
a fast and portable software suite for combinatorial optimization
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operations_research::LazySteepestSearch Class Reference

#include <set_cover_heuristics.h>

Inheritance diagram for operations_research::LazySteepestSearch:
operations_research::BoolVectorBasedSolutionGenerator operations_research::SetCoverSolutionGenerator

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)
SetCoverInvariantinv () const
virtual SetCoverSolutionGeneratorResetLimits ()
 Resets the limits to their default values.
SetCoverSolutionGeneratorSetMaxIterations (int64_t max_iterations)
 Sets the maximum number of iterations.
int64_t max_iterations () const
 Returns the maximum number of iterations.
SetCoverSolutionGeneratorSetTimeLimitInSeconds (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
SetCoverModelmodel () 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.

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.

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: