Detailed Description

Deletes as many singleton rows or singleton columns as possible. Note that each time we delete a row or a column, new singletons may be created.

Definition at line 451 of file preprocessor.h.

#include <preprocessor.h>

Inheritance diagram for operations_research::glop::SingletonPreprocessor:

Public Member Functions
	SingletonPreprocessor (const GlopParameters *parameters)
	SingletonPreprocessor (const SingletonPreprocessor &)=delete
SingletonPreprocessor &	operator= (const SingletonPreprocessor &)=delete
	~SingletonPreprocessor () final=default
bool	Run (LinearProgram *lp) final
void	RecoverSolution (ProblemSolution *solution) const final
Public Member Functions inherited from operations_research::glop::Preprocessor
	Preprocessor (const GlopParameters *parameters)
	Preprocessor (const Preprocessor &)=delete
Preprocessor &	operator= (const Preprocessor &)=delete
virtual	~Preprocessor ()
ProblemStatus	status () const
virtual void	UseInMipContext ()
void	SetTimeLimit (TimeLimit *time_limit)

Additional Inherited Members
Protected Member Functions inherited from operations_research::glop::Preprocessor
bool	IsSmallerWithinFeasibilityTolerance (Fractional a, Fractional b) const
bool	IsSmallerWithinPreprocessorZeroTolerance (Fractional a, Fractional b) const
Protected Attributes inherited from operations_research::glop::Preprocessor
ProblemStatus	status_
const GlopParameters &	parameters_
bool	in_mip_context_
std::unique_ptr< TimeLimit >	infinite_time_limit_
TimeLimit *	time_limit_

Constructor & Destructor Documentation

◆ SingletonPreprocessor() [1/2]

operations_research::glop::SingletonPreprocessor::SingletonPreprocessor ( const GlopParameters * parameters )

inlineexplicit

Definition at line 453 of file preprocessor.h.

◆ SingletonPreprocessor() [2/2]

operations_research::glop::SingletonPreprocessor::SingletonPreprocessor ( const SingletonPreprocessor & )

delete

◆ ~SingletonPreprocessor()

operations_research::glop::SingletonPreprocessor::~SingletonPreprocessor ( )

finaldefault

Member Function Documentation

◆ operator=()

SingletonPreprocessor & operations_research::glop::SingletonPreprocessor::operator= ( const SingletonPreprocessor & )

delete

◆ RecoverSolution()

void operations_research::glop::SingletonPreprocessor::RecoverSolution ( ProblemSolution * solution ) const

finalvirtual

Stores the optimal solution of the linear program that was passed to Run(). The given solution needs to be set to the optimal solution of the linear program "modified" by Run().

Note: the two deletion helpers must restore 0.0 values in the positions that will be used during Undo(). That is, all the calls done by this class to MarkColumnForDeletion() should be done with 0.0 as the value to restore (which is already the case when using MarkRowForDeletion()). This is important because the various Undo() functions assume that a primal/dual variable value which isn't restored yet has the value of 0.0.

It is important to undo the operations in the correct order, i.e. in the reverse order in which they were done.

Implements operations_research::glop::Preprocessor.

Definition at line 2940 of file preprocessor.cc.

◆ Run()

bool operations_research::glop::SingletonPreprocessor::Run ( LinearProgram * lp )

finalvirtual

Runs the preprocessor by modifying the given linear program. Returns true if a postsolve step will be needed (i.e. RecoverSolution() is not the identity function). Also updates status_ to something different from ProblemStatus::INIT if the problem was solved (including bad statuses like ProblemStatus::ABNORMAL, ProblemStatus::INFEASIBLE, etc.).

Initialize column_to_process with the current singleton columns.

Initialize row_to_process with the current singleton rows.

Process current singleton rows/columns and enqueue new ones.

Todo: (user): It seems better to process all the singleton columns with a cost of zero first.

We don't want to do a substitution if the entry is too small and should be probably set to zero.

Todo: (user): We should be able to restrict the variable bounds with the ones of the constraint all the time. However, some situation currently break the presolve, and it seems hard to fix in a 100% safe way.