OsiPresolve Class Reference

OSI interface to COIN problem simplification capabilities. More...

#include <OsiPresolve.hpp>

Collaboration diagram for OsiPresolve:

Public Member Functions
	OsiPresolve ()
	Default constructor (empty object).
virtual	~OsiPresolve ()
	Virtual destructor.
virtual OsiSolverInterface *	presolvedModel (OsiSolverInterface &origModel, double feasibilityTolerance=0.0, bool keepIntegers=true, int numberPasses=5, const char *prohibited=NULL, bool doStatus=true, const char *rowProhibited=NULL)
	Create a new OsiSolverInterface loaded with the presolved problem.
OsiSolverInterface *	model () const
	Restate the solution to the presolved problem in terms of the original problem and load it into the original model.
*Return a pointer to the original model OsiSolverInterface *	originalModel () const
*Set the pointer to the original model void	setOriginalModel (OsiSolverInterface *model)
*Return a pointer to the original columns const int *	originalColumns () const
*Return a pointer to the original rows const int *	originalRows () const
*Return number of rows in original model int	getNumRows () const
*Return number of columns in original model int	getNumCols () const
void	setNonLinearValue (double value)
	"Magic" number.
double	nonLinearValue () const

Public Attributes
OsiSolverInterface *	originalModel_
	Fine control over presolve actions.
OsiSolverInterface *	presolvedModel_
	Presolved model (solver interface loaded with the presolved problem).
double	nonLinearValue_
	"Magic" number.
*Original column numbers int *	originalColumn_
*Original row numbers int *	originalRow_
*The list of transformations applied const CoinPresolveAction *	paction_
int	ncols_
	Number of columns in original model.
int	nrows_
	Number of rows in original model.
CoinBigIndex	nelems_
	Number of nonzero matrix coefficients in the original model.
int	presolveActions_
	Whether we want to skip dual part of presolve etc.
*Number of major passes int	numberPasses_

Protected Member Functions
virtual const CoinPresolveAction *	presolve (CoinPresolveMatrix *prob)
	Apply presolve transformations to the problem.
virtual void	postsolve (CoinPostsolveMatrix &prob)
	Reverse presolve transformations to recover the solution to the original problem.
void	gutsOfDestroy ()
	Destroys queued postsolve actions.

Detailed Description

OSI interface to COIN problem simplification capabilities.

COIN provides a number of classes which implement problem simplification algorithms (CoinPresolveAction, CoinPrePostsolveMatrix, and derived classes). The model of operation is as follows:

• Create a copy of the original problem.
• Subject the copy to a series of transformations (the presolve methods) to produce a presolved model. Each transformation is also expected to provide a method to reverse the transformation (the postsolve method). The postsolve methods are collected in a linked list; the postsolve method for the final presolve transformation is at the head of the list.
• Hand the presolved problem to the solver for optimization.
• Apply the collected postsolve methods to the presolved problem and solution, restating the solution in terms of the original problem.

The COIN presolve algorithms are unaware of OSI. The OsiPresolve class takes care of the interface. Given an OsiSolverInterface origModel, it will take care of creating a clone properly loaded with the presolved problem and ready for optimization. After optimization, it will apply postsolve transformations and load the result back into origModel.

Assuming a problem has been loaded into an OsiSolverInterface origModel, a bare-bones application looks like this:

OsiPresolve pinfo ;
OsiSolverInterface *presolvedModel ;
// Return an OsiSolverInterface loaded with the presolved problem.
presolvedModel = pinfo.presolvedModel(*origModel,1.0e-8,false,numberPasses) ;
presolvedModel->initialSolve() ;
// Restate the solution and load it back into origModel.
pinfo.postsolve(true) ;
delete presolvedModel ;

Definition at line 59 of file OsiPresolve.hpp.

Constructor & Destructor Documentation

OsiPresolve()

OsiPresolve::OsiPresolve

(

)

Default constructor (empty object).

~OsiPresolve()

virtual OsiPresolve::~OsiPresolve ( )

virtual

Virtual destructor.

Member Function Documentation

presolvedModel()

virtual OsiSolverInterface * OsiPresolve::presolvedModel ( OsiSolverInterface & origModel, double feasibilityTolerance = 0.0, bool keepIntegers = true, int numberPasses = 5, const char * prohibited = NULL, bool doStatus = true, const char * rowProhibited = NULL )

virtual

Create a new OsiSolverInterface loaded with the presolved problem.

This method implements the first two steps described in the class documentation. It clones origModel and applies presolve transformations, storing the resulting list of postsolve transformations. It returns a pointer to a new OsiSolverInterface loaded with the presolved problem, or NULL if the problem is infeasible or unbounded. If keepIntegers is true then bounds may be tightened in the original. Bounds will be moved by up to feasibilityTolerance to try and stay feasible. When doStatus is true, the current solution will be transformed to match the presolved model.

This should be paired with postsolve(). It is up to the client to destroy the returned OsiSolverInterface, after calling postsolve().

This method is virtual. Override this method if you need to customize the steps of creating a model to apply presolve transformations.

In some sense, a wrapper for presolve(CoinPresolveMatrix*).

model()

OsiSolverInterface * OsiPresolve::model

(

)

const

Restate the solution to the presolved problem in terms of the original problem and load it into the original model.

postsolve() restates the solution in terms of the original problem and updates the original OsiSolverInterface supplied to presolvedModel(). If the problem has not been solved to optimality, there are no guarantees. If you are using an algorithm like simplex that has a concept of a basic solution, then set updateStatus

The advantage of going back to the original problem is that it will be exactly as it was, i.e., 0.0 will not become 1.0e-19.

Note that if you modified the original problem after presolving, then you must ``undo'' these modifications before calling postsolve().

In some sense, a wrapper for postsolve(CoinPostsolveMatrix&). */ virtual void postsolve(bool updateStatus = true);

/*! Return a pointer to the presolved model.

originalModel()

*Return a pointer to the original model OsiSolverInterface * OsiPresolve::originalModel

(

)

const

setOriginalModel()

*Set the pointer to the original model void OsiPresolve::setOriginalModel

(

OsiSolverInterface *

model

)

originalColumns()

*Return a pointer to the original columns const int * OsiPresolve::originalColumns

(

)

const

originalRows()

*Return a pointer to the original rows const int * OsiPresolve::originalRows

(

)

const

getNumRows()

*Return number of rows in original model int OsiPresolve::getNumRows ( ) const

inline

Definition at line 130 of file OsiPresolve.hpp.

getNumCols()

*Return number of columns in original model int OsiPresolve::getNumCols ( ) const

inline

Definition at line 136 of file OsiPresolve.hpp.

setNonLinearValue()

void OsiPresolve::setNonLinearValue ( double value )

inline

"Magic" number.

If this is non-zero then any elements with this value may change and so presolve is very limited in what can be done to the row and column. This is for non-linear problems.

Definition at line 145 of file OsiPresolve.hpp.

nonLinearValue()

double OsiPresolve::nonLinearValue ( ) const

inline

Definition at line 149 of file OsiPresolve.hpp.

presolve()

virtual const CoinPresolveAction * OsiPresolve::presolve ( CoinPresolveMatrix * prob )

protectedvirtual

Apply presolve transformations to the problem.

Handles the core activity of applying presolve transformations.

If you want to apply the individual presolve routines differently, or perhaps add your own to the mix, define a derived class and override this method

postsolve()

virtual void OsiPresolve::postsolve ( CoinPostsolveMatrix & prob )

protectedvirtual

Reverse presolve transformations to recover the solution to the original problem.

Handles the core activity of applying postsolve transformations.

Postsolving is pretty generic; just apply the transformations in reverse order. You will probably only be interested in overriding this method if you want to add code to test for consistency while debugging new presolve techniques.

gutsOfDestroy()

void OsiPresolve::gutsOfDestroy ( )

protected

Destroys queued postsolve actions.

E.g., when presolve() determines the problem is infeasible, so that it will not be necessary to actually solve the presolved problem and convert the result back to the original problem.

Member Data Documentation

originalModel_

OsiSolverInterface* OsiPresolve::originalModel_

Fine control over presolve actions.

Set/clear the following bits to allow or suppress actions:

• 0x01 allow duplicate column processing on integer columns and dual stuff on integers
• 0x02 switch off actions which can change +1 to something else (doubleton, tripleton, implied free)
• 0x04 allow transfer of costs from singletons and between integer variables (when advantageous)
• 0x08 do not allow x+y+z=1 transform
• 0x10 allow actions that don't easily unroll
• 0x20 allow dubious gub element reduction

GUB element reduction is only partially implemented in CoinPresolve (see gubrow_action) and willl cause an abort at postsolve. It's not clear what's meant by `dual stuff on integers'. – lh, 110605 – */ inline void setPresolveActions(int action) { presolveActions_ = (presolveActions_ & 0xffff0000) | (action & 0xffff); } Get presolved model inline OsiSolverInterface *presolvedModel() const { return presolvedModel_; } Set presolved model inline void setPresolvedModel(OsiSolverInterface *presolvedModel) { presolvedModel_ = presolvedModel; }

private: /*! Original model (solver interface loaded with the original problem).

Must not be destroyed until after postsolve().

Definition at line 191 of file OsiPresolve.hpp.

presolvedModel_

OsiSolverInterface* OsiPresolve::presolvedModel_

Presolved model (solver interface loaded with the presolved problem).

Must be destroyed by the client (using delete) after postsolve().

Definition at line 197 of file OsiPresolve.hpp.

nonLinearValue_

double OsiPresolve::nonLinearValue_

"Magic" number.

If this is non-zero then any elements with this value may change and so presolve is very limited in what can be done to the row and column. This is for non-linear problems. One could also allow for cases where sign of coefficient is known.

Definition at line 204 of file OsiPresolve.hpp.

originalColumn_

* Original column numbers int* OsiPresolve::originalColumn_

Definition at line 207 of file OsiPresolve.hpp.

originalRow_

* Original row numbers int* OsiPresolve::originalRow_

Definition at line 210 of file OsiPresolve.hpp.

paction_

* The list of transformations applied const CoinPresolveAction* OsiPresolve::paction_

Definition at line 213 of file OsiPresolve.hpp.

ncols_

int OsiPresolve::ncols_

Number of columns in original model.

The problem will expand back to its former size as postsolve transformations are applied. It is efficient to allocate data structures for the final size of the problem rather than expand them as needed.

Definition at line 221 of file OsiPresolve.hpp.

nrows_

int OsiPresolve::nrows_

Number of rows in original model.

Definition at line 224 of file OsiPresolve.hpp.

nelems_

CoinBigIndex OsiPresolve::nelems_

Number of nonzero matrix coefficients in the original model.

Definition at line 227 of file OsiPresolve.hpp.

presolveActions_

int OsiPresolve::presolveActions_

Whether we want to skip dual part of presolve etc.

1 bit allows duplicate column processing on integer columns and dual stuff on integers 4 transfers costs to integer variables

Definition at line 234 of file OsiPresolve.hpp.

numberPasses_

* Number of major passes int OsiPresolve::numberPasses_

Definition at line 236 of file OsiPresolve.hpp.

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

• /builddir/build/BUILD/coin-or-Osi-0.108.12-build/Osi-releases-0.108.12/Osi/src/Osi/OsiPresolve.hpp