Detailed Description

reduced cost strengthening using root node reduced costs and the cutoff bound

Author: Tobias Achterberg; Stefan Heinz

This propagator uses the root reduced cost to (globally) propagate against the cutoff bound. The propagator checks if the variables with non-zero root reduced cost can exceed the cutoff bound. If this is the case the corresponding bound can be tightened.

The propagate is performed during the search any time a new cutoff bound (primal solution) is found.

Definition in file prop_rootredcost.c.

#include <assert.h>
#include <string.h>
#include "scip/prop_rootredcost.h"

Go to the source code of this file.

Macros
Propagator properties
#define	PROP_NAME "rootredcost"

#define	PROP_DESC "reduced cost strengthening using root node reduced costs and the cutoff bound"

#define	PROP_TIMING SCIP_PROPTIMING_BEFORELP \| SCIP_PROPTIMING_AFTERLPLOOP

#define	PROP_PRIORITY +10000000

#define	PROP_FREQ 1

#define	PROP_DELAY FALSE

Default parameter values
#define	DEFAULT_ONLYBINARY FALSE

#define	DEFAULT_FORCE FALSE

Functions
Local methods
static void	propdataReset (SCIP scip, SCIP_PROPDATA propdata)

static	SCIP_DECL_SORTPTRCOMP (varCompRedcost)

static SCIP_RETCODE	propdataCreate (SCIP scip, SCIP_PROPDATA *propdata)

static int	countNonZeroRootRedcostVars (SCIP scip, SCIP_VAR *vars, int nvars)

static SCIP_RETCODE	propdataExit (SCIP scip, SCIP_PROPDATA propdata)

static SCIP_RETCODE	propdataInit (SCIP scip, SCIP_PROPDATA propdata)

static SCIP_RETCODE	propagateRootRedcostVar (SCIP scip, SCIP_VAR var, SCIP_Real cutoffbound, SCIP_Bool infeasible, SCIP_Bool tightened)

static SCIP_RETCODE	propagateBinaryBestRootRedcost (SCIP scip, SCIP_PROPDATA propdata, SCIP_Real cutoffbound, int nchgbds, SCIP_Bool cutoff)

Callback methods of propagator
static	SCIP_DECL_PROPCOPY (propCopyRootredcost)

static	SCIP_DECL_PROPFREE (propFreeRootredcost)

static	SCIP_DECL_PROPEXITSOL (propExitsolRootredcost)

static	SCIP_DECL_PROPEXEC (propExecRootredcost)

Interface methods
SCIP_RETCODE	SCIPincludePropRootredcost (SCIP *scip)

Macro Definition Documentation

#define PROP_NAME "rootredcost"

Definition at line 45 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define PROP_DESC "reduced cost strengthening using root node reduced costs and the cutoff bound"

Definition at line 46 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define PROP_TIMING SCIP_PROPTIMING_BEFORELP | SCIP_PROPTIMING_AFTERLPLOOP

Definition at line 47 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define PROP_PRIORITY +10000000

propagator priority

Definition at line 48 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define PROP_FREQ 1

propagator frequency

Definition at line 49 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define PROP_DELAY FALSE

should propagation method be delayed, if other propagators found reductions?

Definition at line 50 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define DEFAULT_ONLYBINARY FALSE

should only binary variables be propagated?

Definition at line 58 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

#define DEFAULT_FORCE FALSE

should the propagator be forced even if active pricer are present? Note that the reductions are always valid, but installing an upper bound on priced variables may lead to problems in pricing (existing variables at their upper bound may be priced again since they may have negative reduced costs)

Definition at line 59 of file prop_rootredcost.c.

Referenced by SCIPincludePropRootredcost().

Function Documentation

static void propdataReset	(	SCIP *	scip,
		SCIP_PROPDATA *	propdata
	)

static

reset structure memember of propagator data structure

Parameters

scip	SCIP data structure
propdata	propagator data to reset

Definition at line 95 of file prop_rootredcost.c.

References FALSE, NULL, SCIP_DECL_SORTPTRCOMP(), and SCIP_INVALID.

Referenced by propdataCreate(), and propdataExit().

static SCIP_DECL_SORTPTRCOMP ( varCompRedcost )

static

compare variables with non-zero reduced cost w.r.t. (i) the cutoff bound which would lead to a fixing (ii) variable problem index;

Definition at line 113 of file prop_rootredcost.c.

Referenced by propdataReset().

static SCIP_RETCODE propdataCreate	(	SCIP *	scip,
		SCIP_PROPDATA **	propdata
	)

static

create propagator data structure

Parameters

scip	SCIP data structure
propdata	pointer to store the created propagator data

Definition at line 144 of file prop_rootredcost.c.

References countNonZeroRootRedcostVars(), propdataReset(), SCIP_CALL, SCIP_OKAY, and SCIPallocMemory.

Referenced by SCIPincludePropRootredcost().

static int countNonZeroRootRedcostVars	(	SCIP *	scip,
		SCIP_VAR **	vars,
		int	nvars
	)

static

counts the number of variables with non-zero root reduced cost

Parameters

scip	SCIP data structure
vars	variable array
nvars	number of variables

Definition at line 158 of file prop_rootredcost.c.

References NULL, propdataExit(), SCIP_Real, SCIPisDualfeasZero(), and SCIPvarGetBestRootRedcost().

Referenced by propdataCreate(), and propdataInit().

static SCIP_RETCODE propdataExit	(	SCIP *	scip,
		SCIP_PROPDATA *	propdata
	)

static

free propagator data

Parameters

scip	SCIP data structure
propdata	propagator data

Definition at line 186 of file prop_rootredcost.c.

References propdataInit(), propdataReset(), SCIP_CALL, SCIP_OKAY, SCIPfreeMemoryArrayNull, and SCIPreleaseVar().

Referenced by countNonZeroRootRedcostVars().

static SCIP_RETCODE propdataInit	(	SCIP *	scip,
		SCIP_PROPDATA *	propdata
	)

static

initializate the propagator

Parameters

scip	SCIP data structure
propdata	propagator data

Definition at line 209 of file prop_rootredcost.c.

References countNonZeroRootRedcostVars(), NULL, propagateRootRedcostVar(), SCIP_CALL, SCIP_OKAY, SCIP_Real, SCIPallocMemoryArray, SCIPcaptureVar(), SCIPdebugMessage, SCIPgetNBinVars(), SCIPgetNVars(), SCIPgetProbName(), SCIPgetVars(), SCIPinfinity(), SCIPisDualfeasZero(), SCIPsortDownPtr(), SCIPvarGetBestRootRedcost(), SCIPvarIsBinary(), and TRUE.

Referenced by propdataExit().

static SCIP_RETCODE propagateRootRedcostVar	(	SCIP *	scip,
		SCIP_VAR *	var,
		SCIP_Real	cutoffbound,
		SCIP_Bool *	infeasible,
		SCIP_Bool *	tightened
	)

static

propagates the root reduced cost against the cutoff bound for the given variable

Parameters

scip	SCIP data structure
var	variable to propagate
cutoffbound	cutoff bound to use
infeasible	pointer to store whether the new domain is empty
tightened	pointer to store if the bound was tightened

Definition at line 309 of file prop_rootredcost.c.

References FALSE, propagateBinaryBestRootRedcost(), SCIP_CALL, SCIP_INVALID, SCIP_OKAY, SCIP_Real, SCIPisDualfeasNegative(), SCIPisDualfeasPositive(), SCIPisDualfeasZero(), SCIPisFeasGE(), SCIPisFeasLE(), SCIPtightenVarLbGlobal(), SCIPtightenVarUbGlobal(), SCIPvarGetBestRootLPObjval(), SCIPvarGetBestRootRedcost(), SCIPvarGetBestRootSol(), SCIPvarGetLbGlobal(), and SCIPvarGetUbGlobal().

Referenced by propagateBinaryBestRootRedcost(), and propdataInit().

static SCIP_RETCODE propagateBinaryBestRootRedcost	(	SCIP *	scip,
		SCIP_PROPDATA *	propdata,
		SCIP_Real	cutoffbound,
		int *	nchgbds,
		SCIP_Bool *	cutoff
	)

static

propagate binary variables with non-zero root reduced cost

Parameters

scip	SCIP data structure
propdata	propagator data structure
cutoffbound	cutoff bound to use
nchgbds	pointer to store the number of bound changes
cutoff	pointer to store if a cutoff was detected