Detailed Description

constraint handler for SOS type 2 constraints

Author: Marc Pfetsch

A specially ordered set of type 2 (SOS2) is a sequence of variables such that at most two variables are nonzero and if two variables are nonzero they must be adjacent in the specified sequence. Note that it is in principle allowed that a variable appears twice, but it then can be fixed to 0 if it is at least two apart in the sequence.

This constraint is useful when considering a piecewise affine approximation of a univariate (nonlinear) function \(: [a,b] \rightarrow R\): Let \(x_1 < \ldots < x_n\) be points in \([a,b]\) and introduce variables \(\lambda_1, \ldots, \lambda_n\). To evaluate \(f(x')\) at some point \(x' \in [a,b]\) one can use the following constraints:

\[ \lambda_1 + \cdots + \lambda_n = 1,\quad x' = x_1 \lambda_1 + \cdots + x_n \lambda_n. \]

The value of \(f(x')\) can the be approximated as

\[ f(x_1) \lambda_1 + \cdots + f(x_n) \lambda_n. \]

To get a valid piecewise affine approximation, \(\lambda_1, \ldots, \lambda_n\) have to obey an SOS constraint of type 2.

This implementation of this constraint handler is based on classical ideas, see e.g.
"Special Facilities in General Mathematical Programming System for Non-Convex Problems Using Ordered Sets of Variables"
E. Beale and J. Tomlin, Proc. 5th IFORS Conference, 447-454 (1970)

The order of the variables is determined as follows:

If the constraint is created with SCIPcreateConsSOS2() and weights are given, the weights determine the order (decreasing weights). Additional variables can be added with SCIPaddVarSOS2(), which adds a variable with given weight.
If an empty constraint is created and then variables are added with SCIPaddVarSOS2(), weights are needed and stored.
All other calls ignore the weights, i.e., if a nonempty constraint is created or variables are added with SCIPappendVarSOS2().

Definition in file cons_sos2.c.

#include "blockmemshell/memory.h"
#include "scip/cons_linear.h"
#include "scip/cons_sos2.h"
#include "scip/pub_cons.h"
#include "scip/pub_event.h"
#include "scip/pub_lp.h"
#include "scip/pub_message.h"
#include "scip/pub_misc.h"
#include "scip/pub_misc_sort.h"
#include "scip/pub_var.h"
#include "scip/scip_branch.h"
#include "scip/scip_conflict.h"
#include "scip/scip_cons.h"
#include "scip/scip_copy.h"
#include "scip/scip_cut.h"
#include "scip/scip_event.h"
#include "scip/scip_general.h"
#include "scip/scip_lp.h"
#include "scip/scip_mem.h"
#include "scip/scip_message.h"
#include "scip/scip_numerics.h"
#include "scip/scip_prob.h"
#include "scip/scip_sol.h"
#include "scip/scip_var.h"
#include "scip/symmetry_graph.h"
#include "symmetry/struct_symmetry.h"
#include <ctype.h>
#include <stdlib.h>
#include <string.h>

Go to the source code of this file.

Macros
#define	CONSHDLR_NAME "SOS2"

#define	CONSHDLR_DESC "SOS2 constraint handler"

#define	CONSHDLR_SEPAPRIORITY 10

#define	CONSHDLR_ENFOPRIORITY 100

#define	CONSHDLR_CHECKPRIORITY -10

#define	CONSHDLR_SEPAFREQ 0

#define	CONSHDLR_PROPFREQ 1

#define	CONSHDLR_EAGERFREQ 100

#define	CONSHDLR_MAXPREROUNDS -1

#define	CONSHDLR_DELAYSEPA FALSE

#define	CONSHDLR_DELAYPROP FALSE

#define	CONSHDLR_NEEDSCONS TRUE

#define	CONSHDLR_PROP_TIMING SCIP_PROPTIMING_BEFORELP

#define	CONSHDLR_PRESOLTIMING SCIP_PRESOLTIMING_FAST

#define	EVENTHDLR_NAME "SOS2"

#define	EVENTHDLR_DESC "bound change event handler for SOS2 constraints"

#define	EVENTHDLR_EVENT_TYPE (SCIP_EVENTTYPE_BOUNDCHANGED \| SCIP_EVENTTYPE_GBDCHANGED)

Functions
static SCIP_RETCODE	fixVariableZeroNode (SCIP scip, SCIP_VAR var, SCIP_NODE node, SCIP_Bool infeasible)

static SCIP_RETCODE	inferVariableZero (SCIP scip, SCIP_VAR var, SCIP_CONS cons, int inferinfo, SCIP_Bool infeasible, SCIP_Bool tightened, SCIP_Bool success)

static SCIP_RETCODE	lockVariableSOS2 (SCIP scip, SCIP_CONS cons, SCIP_VAR *var)

static SCIP_RETCODE	unlockVariableSOS2 (SCIP scip, SCIP_CONS cons, SCIP_VAR *var)

static SCIP_RETCODE	consdataEnsurevarsSizeSOS2 (SCIP scip, SCIP_CONSDATA consdata, int num, SCIP_Bool reserveWeights)

static SCIP_RETCODE	handleNewVariableSOS2 (SCIP scip, SCIP_CONS cons, SCIP_CONSDATA consdata, SCIP_VAR var, SCIP_Bool transformed)

static SCIP_RETCODE	addVarSOS2 (SCIP scip, SCIP_CONS cons, SCIP_VAR *var, SCIP_Real weight)

static SCIP_RETCODE	appendVarSOS2 (SCIP scip, SCIP_CONS cons, SCIP_VAR *var)

static SCIP_RETCODE	deleteVarSOS2 (SCIP scip, SCIP_CONS cons, SCIP_CONSDATA consdata, SCIP_EVENTHDLR eventhdlr, int pos)

static SCIP_RETCODE	presolRoundSOS2 (SCIP scip, SCIP_CONS cons, SCIP_CONSDATA consdata, SCIP_EVENTHDLR eventhdlr, SCIP_Bool cutoff, SCIP_Bool success, int ndelconss, int nfixedvars, int *nremovedvars)

static SCIP_RETCODE	propSOS2 (SCIP scip, SCIP_CONS cons, SCIP_CONSDATA consdata, SCIP_Bool cutoff, int *ngen)

static SCIP_RETCODE	enforceSOS2 (SCIP scip, SCIP_CONSHDLR conshdlr, int nconss, SCIP_CONS *conss, SCIP_SOL sol, SCIP_RESULT *result)

static SCIP_RETCODE	generateRowSOS2 (SCIP scip, SCIP_CONSHDLR conshdlr, SCIP_CONS *cons, SCIP_Bool local)

static	SCIP_DECL_CONSHDLRCOPY (conshdlrCopySOS2)

static	SCIP_DECL_CONSFREE (consFreeSOS2)

static	SCIP_DECL_CONSEXITSOL (consExitsolSOS2)

static	SCIP_DECL_CONSDELETE (consDeleteSOS2)

static	SCIP_DECL_CONSTRANS (consTransSOS2)

static	SCIP_DECL_CONSPRESOL (consPresolSOS2)

static	SCIP_DECL_CONSINITLP (consInitlpSOS2)

static	SCIP_DECL_CONSSEPALP (consSepalpSOS2)

static	SCIP_DECL_CONSSEPASOL (consSepasolSOS2)

static	SCIP_DECL_CONSENFOLP (consEnfolpSOS2)

static	SCIP_DECL_CONSENFORELAX (consEnforelaxSOS2)

static	SCIP_DECL_CONSENFOPS (consEnfopsSOS2)

static	SCIP_DECL_CONSCHECK (consCheckSOS2)

static	SCIP_DECL_CONSPROP (consPropSOS2)

static	SCIP_DECL_CONSRESPROP (consRespropSOS2)

static	SCIP_DECL_CONSLOCK (consLockSOS2)

static	SCIP_DECL_CONSPRINT (consPrintSOS2)

static	SCIP_DECL_CONSCOPY (consCopySOS2)

static	SCIP_DECL_CONSPARSE (consParseSOS2)

static	SCIP_DECL_CONSGETVARS (consGetVarsSOS2)

static	SCIP_DECL_CONSGETNVARS (consGetNVarsSOS2)

static	SCIP_DECL_CONSGETPERMSYMGRAPH (consGetPermsymGraphSOS2)

static	SCIP_DECL_CONSGETSIGNEDPERMSYMGRAPH (consGetSignedPermsymGraphSOS2)

static	SCIP_DECL_EVENTEXEC (eventExecSOS2)

SCIP_RETCODE	SCIPincludeConshdlrSOS2 (SCIP *scip)

SCIP_RETCODE	SCIPcreateConsSOS2 (SCIP scip, SCIP_CONS cons, const char name, int nvars, SCIP_VAR *vars, SCIP_Real weights, SCIP_Bool initial, SCIP_Bool separate, SCIP_Bool enforce, SCIP_Bool check, SCIP_Bool propagate, SCIP_Bool local, SCIP_Bool dynamic, SCIP_Bool removable, SCIP_Bool stickingatnode)

SCIP_RETCODE	SCIPcreateConsBasicSOS2 (SCIP scip, SCIP_CONS cons, const char name, int nvars, SCIP_VAR *vars, SCIP_Real weights)

SCIP_RETCODE	SCIPaddVarSOS2 (SCIP scip, SCIP_CONS cons, SCIP_VAR *var, SCIP_Real weight)

SCIP_RETCODE	SCIPappendVarSOS2 (SCIP scip, SCIP_CONS cons, SCIP_VAR *var)

int	SCIPgetNVarsSOS2 (SCIP scip, SCIP_CONS cons)

SCIP_VAR **	SCIPgetVarsSOS2 (SCIP scip, SCIP_CONS cons)

SCIP_Real *	SCIPgetWeightsSOS2 (SCIP scip, SCIP_CONS cons)

Macro Definition Documentation

◆ CONSHDLR_NAME

◆ CONSHDLR_DESC

#define CONSHDLR_DESC "SOS2 constraint handler"

Definition at line 111 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_SEPAPRIORITY

#define CONSHDLR_SEPAPRIORITY 10

priority of the constraint handler for separation

Definition at line 112 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_ENFOPRIORITY

#define CONSHDLR_ENFOPRIORITY 100

priority of the constraint handler for constraint enforcing

Definition at line 113 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_CHECKPRIORITY

#define CONSHDLR_CHECKPRIORITY -10

priority of the constraint handler for checking feasibility

Definition at line 114 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_SEPAFREQ

#define CONSHDLR_SEPAFREQ 0

frequency for separating cuts; zero means to separate only in the root node

Definition at line 115 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_PROPFREQ

#define CONSHDLR_PROPFREQ 1

frequency for propagating domains; zero means only preprocessing propagation

Definition at line 116 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_EAGERFREQ

#define CONSHDLR_EAGERFREQ 100

frequency for using all instead of only the useful constraints in separation, propagation and enforcement, -1 for no eager evaluations, 0 for first only

Definition at line 117 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_MAXPREROUNDS

#define CONSHDLR_MAXPREROUNDS -1

maximal number of presolving rounds the constraint handler participates in (-1: no limit)

Definition at line 120 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_DELAYSEPA

#define CONSHDLR_DELAYSEPA FALSE

should separation method be delayed, if other separators found cuts?

Definition at line 121 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_DELAYPROP

#define CONSHDLR_DELAYPROP FALSE

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

Definition at line 122 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_NEEDSCONS

#define CONSHDLR_NEEDSCONS TRUE

should the constraint handler be skipped, if no constraints are available?

Definition at line 123 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_PROP_TIMING

#define CONSHDLR_PROP_TIMING SCIP_PROPTIMING_BEFORELP

Definition at line 125 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ CONSHDLR_PRESOLTIMING

#define CONSHDLR_PRESOLTIMING SCIP_PRESOLTIMING_FAST

Definition at line 126 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ EVENTHDLR_NAME

#define EVENTHDLR_NAME "SOS2"

Definition at line 129 of file cons_sos2.c.

Referenced by SCIP_DECL_EVENTEXEC(), and SCIPincludeConshdlrSOS2().

◆ EVENTHDLR_DESC

#define EVENTHDLR_DESC "bound change event handler for SOS2 constraints"

Definition at line 130 of file cons_sos2.c.

Referenced by SCIPincludeConshdlrSOS2().

◆ EVENTHDLR_EVENT_TYPE

#define EVENTHDLR_EVENT_TYPE (SCIP_EVENTTYPE_BOUNDCHANGED | SCIP_EVENTTYPE_GBDCHANGED)

Definition at line 132 of file cons_sos2.c.

Referenced by deleteVarSOS2(), handleNewVariableSOS2(), presolRoundSOS2(), SCIP_DECL_CONSDELETE(), and SCIP_DECL_CONSTRANS().

Function Documentation

◆ fixVariableZeroNode()

static SCIP_RETCODE fixVariableZeroNode	(	SCIP *	scip,
		SCIP_VAR *	var,
		SCIP_NODE *	node,
		SCIP_Bool *	infeasible
	)

static

fix variable in given node to 0 or add constraint if variable is multi-aggregated

Parameters

scip	SCIP pointer
var	variable to be fixed to 0
node	node
infeasible	if fixing is infeasible

Definition at line 155 of file cons_sos2.c.

References FALSE, inferVariableZero(), NULL, SCIP_CALL, SCIP_OKAY, SCIP_Real, SCIP_VARSTATUS_MULTAGGR, SCIPaddConsNode(), SCIPchgVarLbNode(), SCIPchgVarUbNode(), SCIPcreateConsLinear(), SCIPdebugMsg, SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPisFeasZero(), SCIPreleaseCons(), SCIPvarGetLbLocal(), SCIPvarGetName(), SCIPvarGetStatus(), SCIPvarGetUbLocal(), and TRUE.

Referenced by enforceSOS2().

◆ inferVariableZero()

static SCIP_RETCODE inferVariableZero	(	SCIP *	scip,
		SCIP_VAR *	var,
		SCIP_CONS *	cons,
		int	inferinfo,
		SCIP_Bool *	infeasible,
		SCIP_Bool *	tightened,
		SCIP_Bool *	success
	)

static

fix variable in local node to 0, and return whether the operation was feasible

Note: We do not add a linear constraint if the variable is multi-aggregated as in fixVariableZeroNode(), since this would be too time consuming.

Parameters

scip	SCIP pointer
var	variable to be fixed to 0
cons	constraint
inferinfo	info for reverse prop.
infeasible	if fixing is infeasible
tightened	if fixing was performed
success	whether fixing was successful, i.e., variable is not multi-aggregated

Definition at line 206 of file cons_sos2.c.

References FALSE, lockVariableSOS2(), SCIP_Bool, SCIP_CALL, SCIP_OKAY, SCIP_VARSTATUS_MULTAGGR, SCIPinferVarLbCons(), SCIPinferVarUbCons(), SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPvarGetLbLocal(), SCIPvarGetStatus(), SCIPvarGetUbLocal(), and TRUE.

Referenced by fixVariableZeroNode(), and propSOS2().

◆ lockVariableSOS2()

static SCIP_RETCODE lockVariableSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_VAR *	var
	)

static

add lock on variable

Parameters

scip	SCIP data structure
cons	constraint
var	variable

Definition at line 249 of file cons_sos2.c.

References NULL, SCIP_CALL, SCIP_OKAY, SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPlockVarCons(), SCIPvarGetLbGlobal(), SCIPvarGetUbGlobal(), and unlockVariableSOS2().

Referenced by handleNewVariableSOS2(), inferVariableZero(), and presolRoundSOS2().

◆ unlockVariableSOS2()

static SCIP_RETCODE unlockVariableSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_VAR *	var
	)

static

remove lock on variable

Parameters

scip	SCIP data structure
cons	constraint
var	variable

Definition at line 269 of file cons_sos2.c.

References consdataEnsurevarsSizeSOS2(), NULL, SCIP_CALL, SCIP_OKAY, SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPunlockVarCons(), SCIPvarGetLbGlobal(), and SCIPvarGetUbGlobal().

Referenced by deleteVarSOS2(), lockVariableSOS2(), and presolRoundSOS2().

◆ consdataEnsurevarsSizeSOS2()

static SCIP_RETCODE consdataEnsurevarsSizeSOS2	(	SCIP *	scip,
		SCIP_CONSDATA *	consdata,
		int	num,
		SCIP_Bool	reserveWeights
	)

static

ensures that the vars and weights array can store at least num entries

Parameters

scip	SCIP data structure
consdata	constraint data
num	minimum number of entries to store
reserveWeights	whether the weights array is handled

Definition at line 289 of file cons_sos2.c.

References handleNewVariableSOS2(), NULL, SCIP_CALL, SCIP_OKAY, SCIPcalcMemGrowSize(), and SCIPreallocBlockMemoryArray.

Referenced by addVarSOS2(), appendVarSOS2(), and unlockVariableSOS2().

◆ handleNewVariableSOS2()

static SCIP_RETCODE handleNewVariableSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_CONSDATA *	consdata,
		SCIP_VAR *	var,
		SCIP_Bool	transformed
	)

static

handle new variable

Parameters

scip	SCIP data structure
cons	constraint
consdata	constraint data
var	variable
transformed	whether original variable was transformed

Definition at line 317 of file cons_sos2.c.

References addVarSOS2(), EVENTHDLR_EVENT_TYPE, lockVariableSOS2(), NULL, SCIP_CALL, SCIP_OKAY, SCIPaddVarToRow(), SCIPcatchVarEvent(), SCIPchgRowLhs(), SCIPchgRowRhs(), SCIPconsGetHdlr(), SCIPconshdlrGetData(), SCIPisFeasGT(), SCIPisFeasLT(), SCIPisFeasNegative(), SCIPisFeasPositive(), SCIProwGetLhs(), SCIProwGetRhs(), SCIPvarGetLbLocal(), and SCIPvarGetUbLocal().

Referenced by addVarSOS2(), appendVarSOS2(), and consdataEnsurevarsSizeSOS2().

◆ addVarSOS2()

static SCIP_RETCODE addVarSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_VAR *	var,
		SCIP_Real	weight
	)

static

adds a variable to an SOS2 constraint, a position given by weight - ascending order

Parameters

scip	SCIP data structure
cons	constraint
var	variable to add to the constraint
weight	weight to determine position

Definition at line 374 of file cons_sos2.c.

References appendVarSOS2(), consdataEnsurevarsSizeSOS2(), handleNewVariableSOS2(), NULL, SCIP_Bool, SCIP_CALL, SCIP_INVALIDCALL, SCIP_OKAY, SCIPconsGetData(), SCIPconsGetName(), SCIPconsIsTransformed(), SCIPerrorMessage, SCIPgetTransformedVar(), SCIPvarIsTransformed(), and TRUE.

Referenced by handleNewVariableSOS2(), and SCIPaddVarSOS2().

◆ appendVarSOS2()

static SCIP_RETCODE appendVarSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_VAR *	var
	)

static

appends a variable to an SOS2 constraint

Parameters

scip	SCIP data structure
cons	constraint
var	variable to add to the constraint

Definition at line 442 of file cons_sos2.c.

References consdataEnsurevarsSizeSOS2(), deleteVarSOS2(), FALSE, handleNewVariableSOS2(), NULL, SCIP_Bool, SCIP_CALL, SCIP_OKAY, SCIPconsGetData(), SCIPconsIsTransformed(), SCIPgetTransformedVar(), SCIPvarIsTransformed(), and TRUE.

Referenced by addVarSOS2(), and SCIPappendVarSOS2().

◆ deleteVarSOS2()

static SCIP_RETCODE deleteVarSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_CONSDATA *	consdata,
		SCIP_EVENTHDLR *	eventhdlr,
		int	pos
	)

static

deletes a variable of an SOS2 constraint

Parameters

scip	SCIP data structure
cons	constraint
consdata	constraint data
eventhdlr	corresponding event handler
pos	position of variable in array

Definition at line 498 of file cons_sos2.c.

References EVENTHDLR_EVENT_TYPE, NULL, presolRoundSOS2(), SCIP_CALL, SCIP_OKAY, SCIPdropVarEvent(), and unlockVariableSOS2().

Referenced by appendVarSOS2(), and presolRoundSOS2().

◆ presolRoundSOS2()

static SCIP_RETCODE presolRoundSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_CONSDATA *	consdata,
		SCIP_EVENTHDLR *	eventhdlr,
		SCIP_Bool *	cutoff,
		SCIP_Bool *	success,
		int *	ndelconss,
		int *	nfixedvars,
		int *	nremovedvars
	)

static

perform one presolving round

We perform the following presolving steps.

If the bounds of one variable force it to be nonzero, we can fix all other variables with distance at least two to zero. If two variables are certain to be nonzero, we can fix all other variables to 0 and remove the constraint.
All variables fixed to zero, that are at the beginning or end of the constraint can be removed.
We substitute appregated variables.
If a constraint has at most two variables, we delete it.

We currently do not handle the following:

If we have at least two variables fixed to zero next to each-other, that are positioned in the inner part of this constraint, we can delete all but one of these variables.
If a variable appears twice not next to each-other, it can be fixed to 0. If one variable appears next to each-other and is already certain to be nonzero, we can fix all variables.
If a binary variable and its negation appear in the constraint, we might fix variables to zero or can forbid a zero value for them.
When, after removing all zero "border" variables, a constraint with more than two variables has at most two variables that are not fixed to 0, only one of these can take a nonzero value, because these variables need to be the "border" variables of this constraint. The same holds if we have exactly three variables in one constraint and the middle variable is certain to be not zero. In both cases we can upgrade this constraint constraint to an sos1 consisting only of the "border" variables. If these "border" variables are negations of each other, we can delete this constraint.
When, after removing all variables fixed to 0, that are possible, in a constraint each even positioned variable is fixed to 0, we can upgrade this constraint to an sos1 that holds all non-fixed variables.
Extract cliques for all odd and also for all even positioned binary variables

Parameters

scip	SCIP pointer
cons	constraint
consdata	constraint data
eventhdlr	event handler
cutoff	whether a cutoff happened
success	whether we performed a successful reduction
ndelconss	number of deleted constraints
nfixedvars	number of fixed variables
nremovedvars	number of variables removed

Definition at line 558 of file cons_sos2.c.

References deleteVarSOS2(), EVENTHDLR_EVENT_TYPE, FALSE, lockVariableSOS2(), NULL, propSOS2(), SCIP_Bool, SCIP_CALL, SCIP_OKAY, SCIP_Real, SCIPcatchVarEvent(), SCIPconsGetName(), SCIPconsIsModifiable(), SCIPdebugMsg, SCIPdelCons(), SCIPdropVarEvent(), SCIPfixVar(), SCIPgetProbvarSum(), SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPisFeasZero(), SCIPisZero(), SCIPvarGetLbGlobal(), SCIPvarGetLbLocal(), SCIPvarGetName(), SCIPvarGetUbGlobal(), SCIPvarGetUbLocal(), TRUE, and unlockVariableSOS2().

Referenced by deleteVarSOS2(), and SCIP_DECL_CONSPRESOL().

◆ propSOS2()

static SCIP_RETCODE propSOS2	(	SCIP *	scip,
		SCIP_CONS *	cons,
		SCIP_CONSDATA *	consdata,
		SCIP_Bool *	cutoff,
		int *	ngen
	)

static

propagate variables

Parameters

scip	SCIP pointer
cons	constraint
consdata	constraint data
cutoff	whether a cutoff happened
ngen	pointer to incremental counter for domain changes

Definition at line 839 of file cons_sos2.c.

References enforceSOS2(), FALSE, inferVariableZero(), NULL, SCIP_Bool, SCIP_CALL, SCIP_OKAY, SCIPconsGetName(), SCIPconsIsModifiable(), SCIPdebugMsg, SCIPdelConsLocal(), SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPresetConsAge(), SCIPvarGetLbLocal(), SCIPvarGetName(), SCIPvarGetUbLocal(), and TRUE.

Referenced by enforceSOS2(), presolRoundSOS2(), and SCIP_DECL_CONSPROP().

◆ enforceSOS2()

static SCIP_RETCODE enforceSOS2	(	SCIP *	scip,
		SCIP_CONSHDLR *	conshdlr,
		int	nconss,
		SCIP_CONS **	conss,
		SCIP_SOL *	sol,
		SCIP_RESULT *	result
	)

static

enforcement method

We check whether the current solution is feasible, i.e., contains at most one nonzero variable. If not, we branch along the lines indicated by Beale and Tomlin:

We first compute \(W = \sum_{j=1}^n |x_i|\) and \(w = \sum_{j=1}^n j\, |x_i|\). Then we search for the index \(k\) that satisfies

\[ k \leq \frac{w}{W} < k+1. \]

The branches are then

\[ x_1 = 0, \ldots, x_{k-1} = 0 \qquad \mbox{and}\qquad x_{k+1} = 0, \ldots, x_n = 0. \]

There is one special case that we have to consider: It can happen that \(k\) is one too small. Example: \(x_1 = 1 - \epsilon, x_2 = 0, x_3 = \epsilon\). Then \(w = 1 - \epsilon + 3 \epsilon = 1 + 2 \epsilon\). This yields \(k = 1\) and hence the first branch does not change the solution. We therefore increase \(k\) by one if \(x_k \neq 0\). This is valid, since we know that \(x_{k+1} \neq 0\) (with respect to the original \(k\)); the corresponding branch will cut off the current solution, since \(x_k \neq 0\).

Parameters

scip	SCIP pointer
conshdlr	constraint handler
nconss	number of constraints
conss	indicator constraints
sol	solution to be enforced (NULL for LP solution)
result	result

Definition at line 1037 of file cons_sos2.c.

References branchCons(), fixVariableZeroNode(), generateRowSOS2(), NULL, propSOS2(), REALABS, SCIP_Bool, SCIP_BRANCHDIR_DOWNWARDS, SCIP_BRANCHED, SCIP_CALL, SCIP_CUTOFF, SCIP_FEASIBLE, SCIP_OKAY, SCIP_Real, SCIP_REDUCEDDOM, SCIPcalcChildEstimateIncrease(), SCIPcalcNodeselPriority(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPcreateChild(), SCIPdebugMsg, SCIPfeasFloor(), SCIPgetLocalTransEstimate(), SCIPgetSolVal(), SCIPisFeasZero(), SCIPresetConsAge(), SCIPvarGetName(), and w.

Referenced by propSOS2(), SCIP_DECL_CONSENFOLP(), SCIP_DECL_CONSENFOPS(), and SCIP_DECL_CONSENFORELAX().

◆ generateRowSOS2()

static SCIP_RETCODE generateRowSOS2	(	SCIP *	scip,
		SCIP_CONSHDLR *	conshdlr,
		SCIP_CONS *	cons,
		SCIP_Bool	local
	)

static

Generate basic row

We generate the row corresponding to the following simple valid inequalities. Let \(U\) and \(U'\) be the largest and second largest upper bound of variables appearing in the constraint. Similarly let \(L\) and \(L'\) be the smallest and second smallest lower bound. The inequalities are:

\[ x_1 + \ldots + x_n \leq U + U' \qquad\mbox{and}\qquad x_1 + \ldots + x_n \geq L + L'. \]

Of course, these inequalities are only added if the upper and lower bounds are all finite and \(L+L' < 0\) or \(U+U' > 0\).

Parameters

scip	SCIP pointer
conshdlr	constraint handler
cons	constraint
local	produce local cut?

Definition at line 1239 of file cons_sos2.c.

References FALSE, NULL, REALABS, SCIP_CALL, SCIP_DECL_CONSHDLRCOPY(), SCIP_MAXSTRLEN, SCIP_OKAY, SCIP_Real, SCIPaddVarsToRowSameCoef(), SCIPconsGetData(), SCIPconsGetName(), SCIPcreateEmptyRowCons(), SCIPdebug, SCIPinfinity(), SCIPisFeasZero(), SCIPisInfinity(), SCIPprintRow(), SCIPsnprintf(), SCIPvarGetLbGlobal(), SCIPvarGetLbLocal(), SCIPvarGetUbGlobal(), and SCIPvarGetUbLocal().

Referenced by enforceSOS2(), SCIP_DECL_CONSINITLP(), SCIP_DECL_CONSSEPALP(), and SCIP_DECL_CONSSEPASOL().

◆ SCIP_DECL_CONSHDLRCOPY()

static SCIP_DECL_CONSHDLRCOPY ( conshdlrCopySOS2 )

static

copy method for constraint handler plugins (called when SCIP copies plugins)

Definition at line 1338 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, SCIP_CALL, SCIP_DECL_CONSFREE(), SCIP_OKAY, SCIPconshdlrGetName(), SCIPincludeConshdlrSOS2(), and TRUE.

Referenced by generateRowSOS2().

◆ SCIP_DECL_CONSFREE()

static SCIP_DECL_CONSFREE ( consFreeSOS2 )

static

destructor of constraint handler to free constraint handler data (called when SCIP is exiting)

Definition at line 1355 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, SCIP_DECL_CONSEXITSOL(), SCIP_OKAY, SCIPconshdlrGetData(), SCIPconshdlrGetName(), and SCIPfreeBlockMemory.

Referenced by SCIP_DECL_CONSHDLRCOPY().

◆ SCIP_DECL_CONSEXITSOL()

static SCIP_DECL_CONSEXITSOL ( consExitsolSOS2 )

static

solving process deinitialization method of constraint handler (called before branch and bound process data is freed)

Definition at line 1374 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, SCIP_CALL, SCIP_DECL_CONSDELETE(), SCIP_OKAY, SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebugMsg, and SCIPreleaseRow().

Referenced by SCIP_DECL_CONSFREE().

◆ SCIP_DECL_CONSDELETE()

static SCIP_DECL_CONSDELETE ( consDeleteSOS2 )

static

frees specific constraint data

Definition at line 1406 of file cons_sos2.c.

References CONSHDLR_NAME, EVENTHDLR_EVENT_TYPE, NULL, SCIP_CALL, SCIP_DECL_CONSTRANS(), SCIP_OKAY, SCIPconsGetName(), SCIPconshdlrGetData(), SCIPconshdlrGetName(), SCIPconsIsTransformed(), SCIPdebugMsg, SCIPdropVarEvent(), SCIPfreeBlockMemory, SCIPfreeBlockMemoryArray, and SCIPreleaseRow().

Referenced by SCIP_DECL_CONSEXITSOL().

◆ SCIP_DECL_CONSTRANS()

static SCIP_DECL_CONSTRANS ( consTransSOS2 )

static

transforms constraint data into data belonging to the transformed problem

Definition at line 1455 of file cons_sos2.c.

References CONSHDLR_NAME, EVENTHDLR_EVENT_TYPE, NULL, SCIP_CALL, SCIP_DECL_CONSPRESOL(), SCIP_MAXSTRLEN, SCIP_OKAY, SCIPallocBlockMemory, SCIPallocBlockMemoryArray, SCIPcatchVarEvent(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetData(), SCIPconshdlrGetName(), SCIPconsIsChecked(), SCIPconsIsDynamic(), SCIPconsIsEnforced(), SCIPconsIsInitial(), SCIPconsIsLocal(), SCIPconsIsModifiable(), SCIPconsIsPropagated(), SCIPconsIsRemovable(), SCIPconsIsSeparated(), SCIPconsIsStickingAtNode(), SCIPcreateCons(), SCIPdebugMsg, SCIPduplicateBlockMemoryArray, SCIPgetTransformedVar(), SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPsnprintf(), SCIPvarGetLbLocal(), and SCIPvarGetUbLocal().

Referenced by SCIP_DECL_CONSDELETE().

◆ SCIP_DECL_CONSPRESOL()

static SCIP_DECL_CONSPRESOL ( consPresolSOS2 )

static

presolving method of constraint handler

Definition at line 1538 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, presolRoundSOS2(), SCIP_Bool, SCIP_CALL, SCIP_CUTOFF, SCIP_DECL_CONSINITLP(), SCIP_DIDNOTFIND, SCIP_DIDNOTRUN, SCIP_OKAY, SCIP_SUCCESS, SCIPconsGetData(), SCIPconshdlrGetData(), SCIPconshdlrGetName(), SCIPconsIsModifiable(), SCIPdebug, and SCIPdebugMsg.

Referenced by SCIP_DECL_CONSTRANS().

◆ SCIP_DECL_CONSINITLP()

static SCIP_DECL_CONSINITLP ( consInitlpSOS2 )

static

LP initialization method of constraint handler (called before the initial LP relaxation at a node is solved)

Definition at line 1607 of file cons_sos2.c.

References CONSHDLR_NAME, FALSE, generateRowSOS2(), NULL, REALABS, SCIP_CALL, SCIP_DECL_CONSSEPALP(), SCIP_OKAY, SCIPaddRow(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebug, SCIPdebugMsg, SCIPisInfinity(), SCIPprintRow(), SCIProwGetLhs(), SCIProwGetRhs(), and SCIProwIsInLP().

Referenced by SCIP_DECL_CONSPRESOL().

◆ SCIP_DECL_CONSSEPALP()

static SCIP_DECL_CONSSEPALP ( consSepalpSOS2 )

static

separation method of constraint handler for LP solutions

Definition at line 1651 of file cons_sos2.c.

References CONSHDLR_NAME, FALSE, generateRowSOS2(), NULL, SCIP_Bool, SCIP_CALL, SCIP_CUTOFF, SCIP_DECL_CONSSEPASOL(), SCIP_DIDNOTFIND, SCIP_DIDNOTRUN, SCIP_OKAY, SCIP_SEPARATED, SCIPaddRow(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebug, SCIPdebugMsg, SCIPisCutEfficacious(), SCIPprintRow(), SCIPresetConsAge(), and SCIProwIsInLP().

Referenced by SCIP_DECL_CONSINITLP().

◆ SCIP_DECL_CONSSEPASOL()

static SCIP_DECL_CONSSEPASOL ( consSepasolSOS2 )

static

separation method of constraint handler for arbitrary primal solutions

Definition at line 1707 of file cons_sos2.c.

References CONSHDLR_NAME, FALSE, generateRowSOS2(), NULL, SCIP_Bool, SCIP_CALL, SCIP_CUTOFF, SCIP_DECL_CONSENFOLP(), SCIP_DIDNOTFIND, SCIP_DIDNOTRUN, SCIP_OKAY, SCIP_SEPARATED, SCIPaddRow(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebug, SCIPdebugMsg, SCIPisCutEfficacious(), SCIPprintRow(), SCIPresetConsAge(), and SCIProwIsInLP().

Referenced by SCIP_DECL_CONSSEPALP().

◆ SCIP_DECL_CONSENFOLP()

static SCIP_DECL_CONSENFOLP ( consEnfolpSOS2 )

static

constraint enforcing method of constraint handler for LP solutions

Definition at line 1763 of file cons_sos2.c.

References CONSHDLR_NAME, enforceSOS2(), NULL, SCIP_CALL, SCIP_DECL_CONSENFORELAX(), SCIP_OKAY, and SCIPconshdlrGetName().

Referenced by SCIP_DECL_CONSSEPASOL().

◆ SCIP_DECL_CONSENFORELAX()

static SCIP_DECL_CONSENFORELAX ( consEnforelaxSOS2 )

static

constraint enforcing method of constraint handler for relaxation solutions

Definition at line 1779 of file cons_sos2.c.

References CONSHDLR_NAME, enforceSOS2(), NULL, SCIP_CALL, SCIP_DECL_CONSENFOPS(), SCIP_OKAY, and SCIPconshdlrGetName().

Referenced by SCIP_DECL_CONSENFOLP().

◆ SCIP_DECL_CONSENFOPS()

static SCIP_DECL_CONSENFOPS ( consEnfopsSOS2 )

static

constraint enforcing method of constraint handler for pseudo solutions

Definition at line 1795 of file cons_sos2.c.

References CONSHDLR_NAME, enforceSOS2(), NULL, SCIP_CALL, SCIP_DECL_CONSCHECK(), SCIP_OKAY, and SCIPconshdlrGetName().

Referenced by SCIP_DECL_CONSENFORELAX().

◆ SCIP_DECL_CONSCHECK()

static SCIP_DECL_CONSCHECK ( consCheckSOS2 )

static

feasibility check method of constraint handler for integral solutions

We simply check whether at most two variable are nonzero and in the case there are exactly two nonzero, then they have to be direct neighbors in the given solution.

Definition at line 1816 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, SCIP_CALL, SCIP_DECL_CONSPROP(), SCIP_FEASIBLE, SCIP_INFEASIBLE, SCIP_OKAY, SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebugMsg, SCIPgetSolVal(), SCIPinfoMessage(), SCIPisFeasZero(), SCIPprintCons(), SCIPresetConsAge(), SCIPupdateSolConsViolation(), and SCIPvarGetName().

Referenced by SCIP_DECL_CONSENFOPS().

◆ SCIP_DECL_CONSPROP()

static SCIP_DECL_CONSPROP ( consPropSOS2 )

static

domain propagation method of constraint handler

Definition at line 1885 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, propSOS2(), SCIP_Bool, SCIP_CALL, SCIP_CUTOFF, SCIP_DECL_CONSRESPROP(), SCIP_DIDNOTFIND, SCIP_DIDNOTRUN, SCIP_OKAY, SCIP_REDUCEDDOM, SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebugMsg, and SCIPisTransformed().

Referenced by SCIP_DECL_CONSCHECK().

◆ SCIP_DECL_CONSRESPROP()

static SCIP_DECL_CONSRESPROP ( consRespropSOS2 )

static

propagation conflict resolving method of constraint handler

We check which bound changes were the reason for infeasibility. We use that inferinfo stores the index of the variable that has bounds that fix it to be nonzero (these bounds are the reason).

Definition at line 1934 of file cons_sos2.c.

References CONSHDLR_NAME, FALSE, NULL, SCIP_CALL, SCIP_DECL_CONSLOCK(), SCIP_DIDNOTFIND, SCIP_OKAY, SCIP_SUCCESS, SCIPaddConflictLb(), SCIPaddConflictUb(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebugMsg, SCIPgetVarLbAtIndex(), SCIPgetVarUbAtIndex(), SCIPisFeasNegative(), and SCIPisFeasPositive().

Referenced by SCIP_DECL_CONSPROP().

◆ SCIP_DECL_CONSLOCK()

static SCIP_DECL_CONSLOCK ( consLockSOS2 )

static

variable rounding lock method of constraint handler

Let lb and ub be the lower and upper bounds of a variable. Preprocessing usually makes sure that lb <= 0 <= ub.

If lb < 0 then rounding down may violate the constraint.
If ub > 0 then rounding up may violated the constraint.
If lb > 0 or ub < 0 then the constraint is infeasible and we do not have to deal with it here.
If lb == 0 then rounding down does not violate the constraint.
If ub == 0 then rounding up does not violate the constraint.

Definition at line 1986 of file cons_sos2.c.

References CONSHDLR_NAME, NULL, SCIP_CALL, SCIP_DECL_CONSPRINT(), SCIP_LOCKTYPE_MODEL, SCIP_OKAY, SCIPaddVarLocksType(), SCIPconsGetData(), SCIPconsGetName(), SCIPconshdlrGetName(), SCIPdebugMsg, SCIPisFeasNegative(), SCIPisFeasPositive(), SCIPvarGetLbGlobal(), and SCIPvarGetUbGlobal().