Scippy

SCIP

Solving Constraint Integer Programs

Detailed Description

optimization-based bound tightening propagator

Author
Stefan Weltge
Benjamin Mueller

Definition in file prop_obbt.c.

#include <assert.h>
#include <string.h>
#include "scip/cons_linear.h"
#include "scip/cons_nonlinear.h"
#include "scip/nlhdlr_bilinear.h"
#include "scip/prop_genvbounds.h"
#include "scip/prop_obbt.h"
#include "scip/pub_cons.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_nlp.h"
#include "scip/pub_prop.h"
#include "scip/pub_tree.h"
#include "scip/pub_var.h"
#include "scip/scip_cons.h"
#include "scip/scip_copy.h"
#include "scip/scip_cut.h"
#include "scip/scip_general.h"
#include "scip/scip_lp.h"
#include "scip/scip_mem.h"
#include "scip/scip_message.h"
#include "scip/scip_nlp.h"
#include "scip/scip_numerics.h"
#include "scip/scip_param.h"
#include "scip/scip_prob.h"
#include "scip/scip_probing.h"
#include "scip/scip_prop.h"
#include "scip/scip_randnumgen.h"
#include "scip/scip_solvingstats.h"
#include "scip/scip_tree.h"
#include "scip/scip_var.h"

Go to the source code of this file.

Data Structures

struct  Bound
 
struct  BilinBound
 

Macros

#define PROP_NAME   "obbt"
 
#define PROP_DESC   "optimization-based bound tightening propagator"
 
#define PROP_TIMING   SCIP_PROPTIMING_AFTERLPLOOP
 
#define PROP_PRIORITY   -1000000
 
#define PROP_FREQ   0
 
#define PROP_DELAY   TRUE
 
#define DEFAULT_CREATE_GENVBOUNDS   TRUE
 
#define DEFAULT_FILTERING_NORM   TRUE
 
#define DEFAULT_APPLY_FILTERROUNDS   FALSE
 
#define DEFAULT_APPLY_TRIVIALFITLERING   TRUE
 
#define DEFAULT_GENVBDSDURINGFILTER   TRUE
 
#define DEFAULT_DUALFEASTOL   1e-9
 
#define DEFAULT_CONDITIONLIMIT   -1.0
 
#define DEFAULT_BOUNDSTREPS   0.001
 
#define DEFAULT_FILTERING_MIN   2
 
#define DEFAULT_ITLIMITFACTOR   10.0
 
#define DEFAULT_MINITLIMIT   5000L
 
#define DEFAULT_ONLYNONCONVEXVARS   TRUE
 
#define DEFAULT_TIGHTINTBOUNDSPROBING   TRUE
 
#define DEFAULT_TIGHTCONTBOUNDSPROBING   FALSE
 
#define DEFAULT_ORDERINGALGO   1
 
#define OBBT_SCOREBASE   5
 
#define GENVBOUND_PROP_NAME   "genvbounds"
 
#define DEFAULT_SEPARATESOL   FALSE
 
#define DEFAULT_SEPAMINITER   0
 
#define DEFAULT_SEPAMAXITER   10
 
#define DEFAULT_GENVBDSDURINGSEPA   TRUE
 
#define DEFAULT_PROPAGATEFREQ   0
 
#define DEFAULT_CREATE_BILININEQS   TRUE
 
#define DEFAULT_CREATE_LINCONS   FALSE
 
#define DEFAULT_ITLIMITFAC_BILININEQS   3.0
 
#define DEFAULT_MINNONCONVEXITY   1e-1
 
#define DEFAULT_RANDSEED   149
 

Typedefs

typedef struct Bound BOUND
 
typedef enum Corner CORNER
 
typedef struct BilinBound BILINBOUND
 

Enumerations

enum  Corner {
  LEFTBOTTOM = 1,
  RIGHTBOTTOM = 2,
  RIGHTTOP = 4,
  LEFTTOP = 8,
  FILTERED = 15
}
 

Functions

static SCIP_RETCODE solveLP (SCIP *scip, int itlimit, SCIP_Bool *error, SCIP_Bool *optimal)
 
static SCIP_RETCODE addObjCutoff (SCIP *scip, SCIP_PROPDATA *propdata)
 
static SCIP_Bool varIsFixedLocal (SCIP *scip, SCIP_VAR *var)
 
static SCIP_RETCODE setObjProbing (SCIP *scip, SCIP_PROPDATA *propdata, BOUND *bound, SCIP_Real coef)
 
static SCIP_Bool includeVarGenVBound (SCIP *scip, SCIP_VAR *var)
 
static int getIterationsLeft (SCIP *scip, SCIP_Longint nolditerations, SCIP_Longint itlimit)
 
static SCIP_Real getFilterCoef (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_VAR *var, SCIP_BOUNDTYPE boundtype)
 
static SCIP_RETCODE createGenVBound (SCIP *scip, SCIP_PROPDATA *propdata, BOUND *bound, SCIP_Bool *found)
 
static void exchangeBounds (SCIP_PROPDATA *propdata, int i)
 
static void getCorner (SCIP_VAR *x, SCIP_VAR *y, CORNER corner, SCIP_Real *px, SCIP_Real *py)
 
static void getCorners (SCIP_VAR *x, SCIP_VAR *y, CORNER corner, SCIP_Real *xs, SCIP_Real *ys, SCIP_Real *xt, SCIP_Real *yt)
 
static SCIP_VARbilinboundGetX (BILINBOUND *bilinbound)
 
static SCIP_VARbilinboundGetY (BILINBOUND *bilinbound)
 
static int bilinboundGetLocksNeg (BILINBOUND *bilinbound)
 
static int bilinboundGetLocksPos (BILINBOUND *bilinbound)
 
static SCIP_Real bilinboundGetScore (SCIP *scip, SCIP_RANDNUMGEN *randnumgen, BILINBOUND *bilinbound)
 
static SCIP_RETCODE filterExistingLP (SCIP *scip, SCIP_PROPDATA *propdata, int *nfiltered, BOUND *currbound)
 
static SCIP_RETCODE filterRound (SCIP *scip, SCIP_PROPDATA *propdata, int itlimit, int *nfiltered, SCIP_Real *objcoefs, int *objcoefsinds, int nobjcoefs)
 
static SCIP_RETCODE filterBounds (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_Longint itlimit)
 
static SCIP_RETCODE applyBoundChgs (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_RESULT *result)
 
static SCIP_RETCODE tightenBoundProbing (SCIP *scip, BOUND *bound, SCIP_Real newval, SCIP_Bool *tightened)
 
static SCIP_DECL_SORTPTRCOMP (compBoundsScore)
 
static SCIP_DECL_SORTPTRCOMP (compBilinboundsScore)
 
static SCIP_DECL_SORTPTRCOMP (compBoundsBoundtype)
 
static SCIP_RETCODE sortBounds (SCIP *scip, SCIP_PROPDATA *propdata)
 
static SCIP_Real evalBound (SCIP *scip, BOUND *bound)
 
static int nextBound (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_Bool convexphase)
 
static SCIP_RETCODE applySeparation (SCIP *scip, SCIP_PROPDATA *propdata, BOUND *currbound, SCIP_Longint *nleftiterations, SCIP_Bool *success)
 
static SCIP_RETCODE findNewBounds (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_Longint *nleftiterations, SCIP_Bool convexphase)
 
static SCIP_RETCODE applyObbt (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_Longint itlimit, SCIP_RESULT *result)
 
static SCIP_RETCODE solveBilinearLP (SCIP *scip, SCIP_VAR *x, SCIP_VAR *y, SCIP_Real xs, SCIP_Real ys, SCIP_Real xt, SCIP_Real yt, SCIP_Real *xcoef, SCIP_Real *ycoef, SCIP_Real *constant, SCIP_Longint iterlim, int *nnonzduals)
 
static SCIP_RETCODE applyObbtBilinear (SCIP *scip, SCIP_PROPDATA *propdata, SCIP_Longint itlimit, SCIP_RESULT *result)
 
static unsigned int getScore (SCIP *scip, BOUND *bound, int nlcount, int maxnlcount)
 
static SCIP_RETCODE getNLPVarsNonConvexity (SCIP *scip, unsigned int *nccounts)
 
static SCIP_Bool varIsInteresting (SCIP *scip, SCIP_VAR *var, int nlcount)
 
static SCIP_RETCODE initBounds (SCIP *scip, SCIP_PROPDATA *propdata)
 
static SCIP_DECL_PROPCOPY (propCopyObbt)
 
static SCIP_DECL_PROPINITSOL (propInitsolObbt)
 
static SCIP_DECL_PROPEXEC (propExecObbt)
 
static SCIP_DECL_PROPRESPROP (propRespropObbt)
 
static SCIP_DECL_PROPEXITSOL (propExitsolObbt)
 
static SCIP_DECL_PROPFREE (propFreeObbt)
 
SCIP_RETCODE SCIPincludePropObbt (SCIP *scip)
 

Macro Definition Documentation

◆ PROP_NAME

#define PROP_NAME   "obbt"

Definition at line 82 of file prop_obbt.c.

Referenced by SCIP_DECL_PROPCOPY().

◆ PROP_DESC

#define PROP_DESC   "optimization-based bound tightening propagator"

Definition at line 83 of file prop_obbt.c.

◆ PROP_TIMING

#define PROP_TIMING   SCIP_PROPTIMING_AFTERLPLOOP

Definition at line 84 of file prop_obbt.c.

◆ PROP_PRIORITY

#define PROP_PRIORITY   -1000000

propagator priority

Definition at line 85 of file prop_obbt.c.

◆ PROP_FREQ

#define PROP_FREQ   0

propagator frequency

Definition at line 86 of file prop_obbt.c.

◆ PROP_DELAY

#define PROP_DELAY   TRUE

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

Definition at line 87 of file prop_obbt.c.

◆ DEFAULT_CREATE_GENVBOUNDS

#define DEFAULT_CREATE_GENVBOUNDS   TRUE

should obbt try to provide genvbounds if possible?

Definition at line 91 of file prop_obbt.c.

◆ DEFAULT_FILTERING_NORM

#define DEFAULT_FILTERING_NORM   TRUE

should coefficients in filtering be normalized w.r.t. the domains sizes?

Definition at line 92 of file prop_obbt.c.

◆ DEFAULT_APPLY_FILTERROUNDS

#define DEFAULT_APPLY_FILTERROUNDS   FALSE

try to filter bounds in so-called filter rounds by solving auxiliary LPs?

Definition at line 95 of file prop_obbt.c.

◆ DEFAULT_APPLY_TRIVIALFITLERING

#define DEFAULT_APPLY_TRIVIALFITLERING   TRUE

should obbt try to use the LP solution to filter some bounds?

Definition at line 98 of file prop_obbt.c.

◆ DEFAULT_GENVBDSDURINGFILTER

#define DEFAULT_GENVBDSDURINGFILTER   TRUE

try to genrate genvbounds during trivial and aggressive filtering?

Definition at line 99 of file prop_obbt.c.

◆ DEFAULT_DUALFEASTOL

#define DEFAULT_DUALFEASTOL   1e-9

feasibility tolerance for reduced costs used in obbt; this value is used if SCIP's dual feastol is greater

Definition at line 100 of file prop_obbt.c.

◆ DEFAULT_CONDITIONLIMIT

#define DEFAULT_CONDITIONLIMIT   -1.0

maximum condition limit used in LP solver (-1.0: no limit)

Definition at line 103 of file prop_obbt.c.

◆ DEFAULT_BOUNDSTREPS

#define DEFAULT_BOUNDSTREPS   0.001

minimal relative improve for strengthening bounds

Definition at line 104 of file prop_obbt.c.

◆ DEFAULT_FILTERING_MIN

#define DEFAULT_FILTERING_MIN   2

minimal number of filtered bounds to apply another filter round

Definition at line 105 of file prop_obbt.c.

◆ DEFAULT_ITLIMITFACTOR

#define DEFAULT_ITLIMITFACTOR   10.0

multiple of root node LP iterations used as total LP iteration limit for obbt (<= 0: no limit )

Definition at line 108 of file prop_obbt.c.

◆ DEFAULT_MINITLIMIT

#define DEFAULT_MINITLIMIT   5000L

minimum LP iteration limit

Definition at line 111 of file prop_obbt.c.

◆ DEFAULT_ONLYNONCONVEXVARS

#define DEFAULT_ONLYNONCONVEXVARS   TRUE

only apply obbt on non-convex variables

Definition at line 112 of file prop_obbt.c.

◆ DEFAULT_TIGHTINTBOUNDSPROBING

#define DEFAULT_TIGHTINTBOUNDSPROBING   TRUE

should bounds of integral variables be tightened during the probing mode?

Definition at line 113 of file prop_obbt.c.

◆ DEFAULT_TIGHTCONTBOUNDSPROBING

#define DEFAULT_TIGHTCONTBOUNDSPROBING   FALSE

should bounds of continuous variables be tightened during the probing mode?

Definition at line 116 of file prop_obbt.c.

◆ DEFAULT_ORDERINGALGO

#define DEFAULT_ORDERINGALGO   1

which type of ordering algorithm should we use? (0: no, 1: greedy, 2: greedy reverse)

Definition at line 119 of file prop_obbt.c.

◆ OBBT_SCOREBASE

#define OBBT_SCOREBASE   5

base that is used to calculate a bounds score value

Definition at line 122 of file prop_obbt.c.

◆ GENVBOUND_PROP_NAME

#define GENVBOUND_PROP_NAME   "genvbounds"

Definition at line 123 of file prop_obbt.c.

◆ DEFAULT_SEPARATESOL

#define DEFAULT_SEPARATESOL   FALSE

should the obbt LP solution be separated? note that that by separating solution OBBT will apply all bound tightenings immediatly

Definition at line 125 of file prop_obbt.c.

◆ DEFAULT_SEPAMINITER

#define DEFAULT_SEPAMINITER   0

minimum number of iteration spend to separate an obbt LP solution

Definition at line 130 of file prop_obbt.c.

◆ DEFAULT_SEPAMAXITER

#define DEFAULT_SEPAMAXITER   10

maximum number of iteration spend to separate an obbt LP solution

Definition at line 131 of file prop_obbt.c.

◆ DEFAULT_GENVBDSDURINGSEPA

#define DEFAULT_GENVBDSDURINGSEPA   TRUE

try to create genvbounds during separation process?

Definition at line 132 of file prop_obbt.c.

◆ DEFAULT_PROPAGATEFREQ

#define DEFAULT_PROPAGATEFREQ   0

trigger a propagation round after that many bound tightenings (0: no propagation)

Definition at line 133 of file prop_obbt.c.

◆ DEFAULT_CREATE_BILININEQS

#define DEFAULT_CREATE_BILININEQS   TRUE

solve auxiliary LPs in order to find valid inequalities for bilinear terms?

Definition at line 136 of file prop_obbt.c.

◆ DEFAULT_CREATE_LINCONS

#define DEFAULT_CREATE_LINCONS   FALSE

create linear constraints from inequalities for bilinear terms?

Definition at line 137 of file prop_obbt.c.

◆ DEFAULT_ITLIMITFAC_BILININEQS

#define DEFAULT_ITLIMITFAC_BILININEQS   3.0

multiple of OBBT LP limit used as total LP iteration limit for solving bilinear inequality LPs (< 0 for no limit)

Definition at line 138 of file prop_obbt.c.

◆ DEFAULT_MINNONCONVEXITY

#define DEFAULT_MINNONCONVEXITY   1e-1

minimum nonconvexity for choosing a bilinear term

Definition at line 139 of file prop_obbt.c.

◆ DEFAULT_RANDSEED

#define DEFAULT_RANDSEED   149

initial random seed

Definition at line 140 of file prop_obbt.c.

Typedef Documentation

◆ BOUND

typedef struct Bound BOUND

Definition at line 159 of file prop_obbt.c.

◆ CORNER

typedef enum Corner CORNER

Definition at line 170 of file prop_obbt.c.

◆ BILINBOUND

typedef struct BilinBound BILINBOUND

Definition at line 180 of file prop_obbt.c.

Enumeration Type Documentation

◆ Corner

enum Corner
Enumerator
LEFTBOTTOM 
RIGHTBOTTOM 
RIGHTTOP 
LEFTTOP 
FILTERED 

Definition at line 162 of file prop_obbt.c.

Function Documentation

◆ solveLP()

static SCIP_RETCODE solveLP ( SCIP scip,
int  itlimit,
SCIP_Bool error,
SCIP_Bool optimal 
)
static

solves the LP and handles errors

Parameters
scipSCIP data structure
itlimitmaximal number of LP iterations to perform, or -1 for no limit
errorpointer to store whether an unresolved LP error occurred
optimalwas the LP solved to optimalilty?

Definition at line 252 of file prop_obbt.c.

Referenced by filterExistingLP().

◆ addObjCutoff()

static SCIP_RETCODE addObjCutoff ( SCIP scip,
SCIP_PROPDATA propdata 
)
static

adds the objective cutoff to the LP; must be in probing mode

Parameters
scipSCIP data structure
propdatadata of the obbt propagator

Definition at line 324 of file prop_obbt.c.

◆ varIsFixedLocal()

static SCIP_Bool varIsFixedLocal ( SCIP scip,
SCIP_VAR var 
)
static

determines, whether a variable is already locally fixed

Parameters
scipSCIP data structure
varvariable to check

Definition at line 374 of file prop_obbt.c.

◆ setObjProbing()

static SCIP_RETCODE setObjProbing ( SCIP scip,
SCIP_PROPDATA propdata,
BOUND bound,
SCIP_Real  coef 
)
static

sets objective to minimize or maximize a single variable

Definition at line 384 of file prop_obbt.c.

Referenced by filterExistingLP().

◆ includeVarGenVBound()

static SCIP_Bool includeVarGenVBound ( SCIP scip,
SCIP_VAR var 
)
static

determines whether variable should be included in the right-hand side of the generalized variable bound

Parameters
scipSCIP data structure
varvariable to check

Definition at line 431 of file prop_obbt.c.

◆ getIterationsLeft()

static int getIterationsLeft ( SCIP scip,
SCIP_Longint  nolditerations,
SCIP_Longint  itlimit 
)
static

returns number of LP iterations left (-1: no limit )

Parameters
scipSCIP data structure
nolditerationsiterations count at the beginning of the corresponding function
itlimitLP iteration limit (-1: no limit)

Definition at line 458 of file prop_obbt.c.

References Bound::boundtype, getFilterCoef(), MAX, NULL, SCIP_Real, SCIPdebugMsg, and SCIPgetNLPIterations().

◆ getFilterCoef()

static SCIP_Real getFilterCoef ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_VAR var,
SCIP_BOUNDTYPE  boundtype 
)
static

returns the objective coefficient for a variable's bound that will be chosen during filtering

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
varvariable
boundtypeboundtype to be filtered?

Definition at line 488 of file prop_obbt.c.

Referenced by getIterationsLeft().

◆ createGenVBound()

static SCIP_RETCODE createGenVBound ( SCIP scip,
SCIP_PROPDATA propdata,
BOUND bound,
SCIP_Bool found 
)
static

creates a genvbound if the dual LP solution provides such information

Consider the problem

min { +/- x_i : obj * x <= z, lb <= Ax <= ub, l <= x <= u },

where z is the current cutoff bound. Let (mu, nu, gamma, alpha, beta) >= 0 be the optimal solution of the dual of problem (P), where the variables correspond to the primal inequalities in the following way:

     Ax >=  lb    <->   mu
    -Ax >= -ub    <->   nu

-obj * x >= -z <-> gamma x >= l <-> alpha -x >= -u <-> beta

Fixing these multipliers, by weak duality, we obtain the inequality

+/- x_i >= lb*mu - ub*nu - z*gamma + l*alpha - u*beta

that holds for all primal feasible points x with objective value at least z. Setting

c = lb*mu - ub*nu, redcost_k = alpha_k - beta_k

we obtain the inequality

+/- x_i >= sum ( redcost_k * x_k ) + (-gamma) * cutoff_bound + c,

that holds for all primal feasible points with objective value at least cutoff_bound. Therefore, the latter inequality can be added as a generalized variable bound.

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
boundbound of x_i
foundpointer to store if we have found a non-trivial genvbound

Definition at line 562 of file prop_obbt.c.

Referenced by filterExistingLP().

◆ exchangeBounds()

static void exchangeBounds ( SCIP_PROPDATA propdata,
int  i 
)
static

exchange a bound which has been processed and updates the last undone and unfiltered bound index NOTE: this method has to be called after filtering or processing a bound

Parameters
propdatapropagator data
ibound that was filtered or processed

Definition at line 748 of file prop_obbt.c.

References NULL.

Referenced by filterExistingLP().

◆ getCorner()

static void getCorner ( SCIP_VAR x,
SCIP_VAR y,
CORNER  corner,
SCIP_Real px,
SCIP_Real py 
)
static

helper function to return a corner of the domain of two variables

Parameters
xfirst variable
ysecond variable
cornercorner
pxbuffer to store point for x
pybuffer to store point for y

Definition at line 771 of file prop_obbt.c.

References FILTERED, getCorners(), LEFTBOTTOM, LEFTTOP, NULL, RIGHTBOTTOM, RIGHTTOP, SCIP_Real, SCIPABORT, SCIPvarGetLbGlobal(), and SCIPvarGetUbGlobal().

Referenced by filterExistingLP().

◆ getCorners()

static void getCorners ( SCIP_VAR x,
SCIP_VAR y,
CORNER  corner,
SCIP_Real xs,
SCIP_Real ys,
SCIP_Real xt,
SCIP_Real yt 
)
static

helper function to return the two end points of a diagonal

Parameters
xfirst variable
ysecond variable
cornercorner
xsbuffer to store start point for x
ysbuffer to store start point for y
xtbuffer to store end point for x
ytbuffer to store end point for y

Definition at line 809 of file prop_obbt.c.

Referenced by getCorner().

◆ bilinboundGetX()

static SCIP_VAR* bilinboundGetX ( BILINBOUND bilinbound)
static

returns the first variable of a bilinear bound

Parameters
bilinboundbilinear bound

Definition at line 851 of file prop_obbt.c.

References BilinBound::expr, NULL, SCIPexprGetChildren(), SCIPexprGetNChildren(), and SCIPgetExprAuxVarNonlinear().

Referenced by bilinboundGetLocksPos(), and filterExistingLP().

◆ bilinboundGetY()

static SCIP_VAR* bilinboundGetY ( BILINBOUND bilinbound)
static

returns the second variable of a bilinear bound

Parameters
bilinboundbilinear bound

Definition at line 863 of file prop_obbt.c.

References bilinboundGetLocksPos(), BilinBound::expr, NULL, and SCIPgetExprNLocksNegNonlinear().

Referenced by bilinboundGetLocksPos(), and filterExistingLP().

◆ bilinboundGetLocksNeg()

static int bilinboundGetLocksNeg ( BILINBOUND bilinbound)
static

returns the negative locks of the expression in a bilinear bound

Parameters
bilinboundbilinear bound

Definition at line 875 of file prop_obbt.c.

References bilinboundGetScore(), BilinBound::expr, NULL, SCIP_Real, and SCIPgetExprNLocksPosNonlinear().

◆ bilinboundGetLocksPos()

static int bilinboundGetLocksPos ( BILINBOUND bilinbound)
static

returns the positive locks of the expression in a bilinear bound

Parameters
bilinboundbilinear bound

Definition at line 886 of file prop_obbt.c.

References bilinboundGetX(), bilinboundGetY(), SCIP_Real, SCIPvarGetLbLocal(), and SCIPvarGetUbLocal().

Referenced by bilinboundGetY().

◆ bilinboundGetScore()

static SCIP_Real bilinboundGetScore ( SCIP scip,
SCIP_RANDNUMGEN randnumgen,
BILINBOUND bilinbound 
)
static

computes the score of a bilinear term bound

Parameters
scipSCIP data structure
randnumgenrandom number generator
bilinboundbilinear bound

Definition at line 897 of file prop_obbt.c.

Referenced by bilinboundGetLocksNeg().

◆ filterExistingLP()

◆ filterRound()

static SCIP_RETCODE filterRound ( SCIP scip,
SCIP_PROPDATA propdata,
int  itlimit,
int *  nfiltered,
SCIP_Real objcoefs,
int *  objcoefsinds,
int  nobjcoefs 
)
static

enforces one round of filtering

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
itlimitLP iteration limit (-1: no limit)
nfilteredhow many bounds were filtered this round
objcoefsarray to store the nontrivial objective coefficients
objcoefsindsarray to store bound indices for which their corresponding variables has a nontrivial objective coefficient
nobjcoefsnumber of nontrivial objective coefficients

Definition at line 1116 of file prop_obbt.c.

Referenced by filterExistingLP().

◆ filterBounds()

static SCIP_RETCODE filterBounds ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_Longint  itlimit 
)
static

filter some bounds that are not improvable by solving auxiliary LPs

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
itlimitLP iteration limit (-1: no limit)

Definition at line 1276 of file prop_obbt.c.

◆ applyBoundChgs()

static SCIP_RETCODE applyBoundChgs ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_RESULT result 
)
static

applies possible bound changes that were found

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
resultresult pointer

Definition at line 1420 of file prop_obbt.c.

◆ tightenBoundProbing()

static SCIP_RETCODE tightenBoundProbing ( SCIP scip,
BOUND bound,
SCIP_Real  newval,
SCIP_Bool tightened 
)
static

tries to tighten a bound in probing mode

Parameters
scipSCIP data structure
boundbound that could be tightened
newvalnew bound value
tightenedwas tightening successful?

Definition at line 1487 of file prop_obbt.c.

◆ SCIP_DECL_SORTPTRCOMP() [1/3]

static SCIP_DECL_SORTPTRCOMP ( compBoundsScore  )
static

comparison method for two bounds w.r.t. their scores

Definition at line 1548 of file prop_obbt.c.

◆ SCIP_DECL_SORTPTRCOMP() [2/3]

static SCIP_DECL_SORTPTRCOMP ( compBilinboundsScore  )
static

comparison method for two bilinear term bounds w.r.t. their scores

Definition at line 1558 of file prop_obbt.c.

◆ SCIP_DECL_SORTPTRCOMP() [3/3]

static SCIP_DECL_SORTPTRCOMP ( compBoundsBoundtype  )
static

comparison method for two bounds w.r.t. their boundtype

Definition at line 1568 of file prop_obbt.c.

References NULL, SCIP_OKAY, SCIPdebugMsg, and SCIPsortDownPtr().

◆ sortBounds()

static SCIP_RETCODE sortBounds ( SCIP scip,
SCIP_PROPDATA propdata 
)
static

sort the propdata->bounds array with their distance or their boundtype key

Parameters
scipSCIP data structure
propdatapropagator data

Definition at line 1594 of file prop_obbt.c.

References Bound::boundtype, NULL, REALABS, SCIP_BOUNDTYPE_LOWER, SCIPvarGetLbLocal(), SCIPvarGetLPSol(), SCIPvarGetUbLocal(), and Bound::var.

◆ evalBound()

static SCIP_Real evalBound ( SCIP scip,
BOUND bound 
)
static

evaluates a bound for the current LP solution

Definition at line 1610 of file prop_obbt.c.

References NULL, and SCIP_Real.

◆ nextBound()

static int nextBound ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_Bool  convexphase 
)
static

returns the index of the next undone and unfiltered bound with the smallest distance

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
convexphaseconsider only convex variables?

Definition at line 1626 of file prop_obbt.c.

◆ applySeparation()

static SCIP_RETCODE applySeparation ( SCIP scip,
SCIP_PROPDATA propdata,
BOUND currbound,
SCIP_Longint nleftiterations,
SCIP_Bool success 
)
static

try to separate the solution of the last OBBT LP in order to learn better variable bounds; we apply additional separation rounds as long as the routine finds better bounds; because of dual degeneracy we apply a minimum number of separation rounds

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
currboundcurrent bound
nleftiterationsnumber of left iterations (-1 for no limit)
successpointer to store if we have found a better bound

Definition at line 1678 of file prop_obbt.c.

◆ findNewBounds()

static SCIP_RETCODE findNewBounds ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_Longint nleftiterations,
SCIP_Bool  convexphase 
)
static

finds new variable bounds until no iterations left or all bounds have been checked

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
nleftiterationspointer to store the number of left iterations
convexphaseconsider only convex variables?

Definition at line 1760 of file prop_obbt.c.

◆ applyObbt()

static SCIP_RETCODE applyObbt ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_Longint  itlimit,
SCIP_RESULT result 
)
static

main function of obbt

Parameters
scipSCIP data structure
propdatadata of the obbt propagator
itlimitLP iteration limit (-1: no limit)
resultresult pointer

Definition at line 1999 of file prop_obbt.c.

Referenced by SCIP_DECL_PROPEXEC().

◆ solveBilinearLP()

static SCIP_RETCODE solveBilinearLP ( SCIP scip,
SCIP_VAR x,
SCIP_VAR y,
SCIP_Real  xs,
SCIP_Real  ys,
SCIP_Real  xt,
SCIP_Real  yt,
SCIP_Real xcoef,
SCIP_Real ycoef,
SCIP_Real constant,
SCIP_Longint  iterlim,
int *  nnonzduals 
)
static

computes a valid inequality from the current LP relaxation for a bilinear term xy only involving x and y; the inequality is found by optimizing along the line connecting the points (xs,ys) and (xt,yt) over the currently given linear relaxation of the problem; this optimization problem is an LP

max lambda s.t. Ax <= b (x,y) = (xs,ys) + lambda ((xt,yt) - (xs,ys)) lambda in [0,1]

which is equivalent to

max x s.t. (1) Ax <= b (2) (x - xs) / (xt - xs) = (y - ys) / (yt - ys)

Let x* be the optimal primal and (mu,theta) be the optimal dual solution of this LP. The KKT conditions imply that the aggregation of the linear constraints mu*Ax <= mu*b can be written as

x * (1 - theta) / (xt - xs) + y * theta / (yt - ys) = mu * Ax <= mu * b

<=> alpha * x + beta * y <= mu * b = alpha * (x*) + beta * (y*)

which is a valid inequality in the (x,y)-space; in order to avoid numerical difficulties when (xs,ys) is too close to (xt,yt), we scale constraint (1) by max{1,|xt-xs|,|yt-ys|} beforehand

Parameters
scipSCIP data structure
xfirst variable
ysecond variable
xsx-coordinate of the first point
ysy-coordinate of the first point
xtx-coordinate of the second point
yty-coordinate of the second point
xcoefpointer to store the coefficient of x
ycoefpointer to store the coefficient of y
constantpointer to store the constant
iterlimiteration limit (-1: for no limit)
nnonzdualsbuffer to store the number of non-zero dual multipliers except for the auxiliary row (NULL if not needed)

Definition at line 2253 of file prop_obbt.c.

References applyObbtBilinear(), FALSE, NULL, r, REALABS, SCIP_Bool, SCIP_CALL, SCIP_INVALID, SCIP_Longint, SCIP_LPSOLSTAT_OPTIMAL, SCIP_OKAY, SCIP_Real, SCIPaddRowProbing(), SCIPaddVarToRow(), SCIPbacktrackProbing(), SCIPchgVarObjProbing(), SCIPcreateEmptyRowUnspec(), SCIPdebugMsg, SCIPgetLPRows(), SCIPgetLPSolstat(), SCIPgetNLPRows(), SCIPinProbing(), SCIPisFeasEQ(), SCIPisFeasZero(), SCIPisHugeValue(), SCIPisZero(), SCIPnewProbingNode(), SCIPreleaseRow(), SCIProwGetDualsol(), SCIPsolveProbingLP(), SCIPvarGetLPSol(), SCIPvarGetName(), SCIPwarningMessage(), and TRUE.

◆ applyObbtBilinear()

static SCIP_RETCODE applyObbtBilinear ( SCIP scip,
SCIP_PROPDATA propdata,
SCIP_Longint  itlimit,
SCIP_RESULT result 
)
static
Parameters
scipSCIP data structure
propdatadata of the obbt propagator
itlimitLP iteration limit (-1: no limit)
resultresult pointer

Definition at line 2401 of file prop_obbt.c.

Referenced by SCIP_DECL_PROPEXEC(), and solveBilinearLP().

◆ getScore()

static unsigned int getScore ( SCIP scip,
BOUND bound,
int  nlcount,
int  maxnlcount 
)
static

computes the score of a bound

Parameters
scipSCIP data structure
boundpointer of bound
nlcountnumber of nonlinear constraints containing the bounds variable
maxnlcountmaximal number of nonlinear constraints a variable appears in

Definition at line 2596 of file prop_obbt.c.

◆ getNLPVarsNonConvexity()

static SCIP_RETCODE getNLPVarsNonConvexity ( SCIP scip,
unsigned int *  nccounts 
)
static

count how often each variable is used in a nonconvex term

Parameters
scipSCIP data structure
nccountsstore the number each variable appears in a non-convex term

Definition at line 2639 of file prop_obbt.c.

◆ varIsInteresting()

static SCIP_Bool varIsInteresting ( SCIP scip,
SCIP_VAR var,
int  nlcount 
)
static

determines whether a variable is interesting

Parameters
scipSCIP data structure
varvariable to check
nlcountnumber of nonlinear constraints containing the variable or number of non-convex terms containing the variable (depends on propdata->onlynonconvexvars)

Definition at line 2698 of file prop_obbt.c.

◆ initBounds()

static SCIP_RETCODE initBounds ( SCIP scip,
SCIP_PROPDATA propdata 
)
static

initializes interesting bounds

Parameters
scipSCIP data structure
propdatadata of the obbt propagator

Definition at line 2714 of file prop_obbt.c.

Referenced by SCIP_DECL_PROPEXEC().

◆ SCIP_DECL_PROPCOPY()

static SCIP_DECL_PROPCOPY ( propCopyObbt  )
static

copy method for propagator plugins (called when SCIP copies plugins)

Note
The UG framework assumes that all default plug-ins of SCIP implement a copy callback. We check SCIPgetSubscipDepth() in PROPEXEC to prevent the propagator to run in a sub-SCIP.

Definition at line 2906 of file prop_obbt.c.

References NULL, PROP_NAME, SCIPpropGetData(), and SCIPpropGetName().

◆ SCIP_DECL_PROPINITSOL()

static SCIP_DECL_PROPINITSOL ( propInitsolObbt  )
static

solving process initialization method of propagator (called when branch and bound process is about to begin)

Definition at line 2920 of file prop_obbt.c.

◆ SCIP_DECL_PROPEXEC()

◆ SCIP_DECL_PROPRESPROP()

static SCIP_DECL_PROPRESPROP ( propRespropObbt  )
static

propagation conflict resolving method of propagator

Definition at line 3064 of file prop_obbt.c.

Referenced by SCIP_DECL_PROPEXEC().

◆ SCIP_DECL_PROPEXITSOL()

static SCIP_DECL_PROPEXITSOL ( propExitsolObbt  )
static

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

Definition at line 3073 of file prop_obbt.c.

Referenced by SCIP_DECL_PROPEXEC().

◆ SCIP_DECL_PROPFREE()

static SCIP_DECL_PROPFREE ( propFreeObbt  )
static

destructor of propagator to free user data (called when SCIP is exiting)

Definition at line 3136 of file prop_obbt.c.