Scippy

SCIP

Solving Constraint Integer Programs

presolve.c File Reference

Detailed Description

methods for presolving

Author
Michael Winkler

Definition in file presolve.c.

#include "scip/mem.h"
#include "scip/presolve.h"
#include "scip/prob.h"
#include "scip/tree.h"
#include "scip/solve.h"
#include "scip/struct_scip.h"

Go to the source code of this file.

Macros

#define CLEARRATIO   0.8
 

Functions

static void collectNonBinaryVBoundData (SCIP *scip, SCIP_VAR *var, int varidx, int pos, int nredvars, SCIP_Real *bounds, SCIP_Bool *boundtypes, SCIP_Real *newbounds, int *counts, int *countnonzeros, int *ncountnonzeros, int *issetvar, int nvars, int *foundbin, int *foundnonbin, int *implidx, int *nimplidx, SCIP_Real *lastbounds)
 
static void collectNonBinaryImplicationData (SCIP *scip, SCIP_VAR *var, int varidx, int pos, int nredvars, SCIP_Bool value, SCIP_Real *bounds, SCIP_Bool *boundtypes, SCIP_Real *newbounds, int *counts, int *countnonzeros, int *ncountnonzeros, int *issetvar, int nvars, int *foundbin, int *foundnonbin, int *implidx, int *nimplidx, SCIP_Real *lastbounds)
 
static void collectBinaryCliqueData (SCIP_VAR *var, int varidx, int pos, int nredvars, SCIP_Bool value, SCIP_Real *bounds, SCIP_Bool *boundtypes, SCIP_Real *newbounds, int *counts, int *countnonzeros, int *ncountnonzeros, int *issetvar, int nvars, int *foundbin, int *implidx, int *nimplidx)
 
SCIP_RETCODE SCIPshrinkDisjunctiveVarSet (SCIP *scip, SCIP_VAR **vars, SCIP_Real *bounds, SCIP_Bool *boundtypes, SCIP_Bool *redundants, int nvars, int *nredvars, int *nglobalred, SCIP_Bool *setredundant, SCIP_Bool *glbinfeas, SCIP_Bool fullshortening)
 

Macro Definition Documentation

#define CLEARRATIO   0.8

Definition at line 930 of file presolve.c.

Referenced by SCIPshrinkDisjunctiveVarSet().

Function Documentation

static void collectNonBinaryVBoundData ( SCIP scip,
SCIP_VAR var,
int  varidx,
int  pos,
int  nredvars,
SCIP_Real bounds,
SCIP_Bool boundtypes,
SCIP_Real newbounds,
int *  counts,
int *  countnonzeros,
int *  ncountnonzeros,
int *  issetvar,
int  nvars,
int *  foundbin,
int *  foundnonbin,
int *  implidx,
int *  nimplidx,
SCIP_Real lastbounds 
)
static

collect variable bound information for a variable set reduction and global implication; only variable which have the vartype != SCIP_VARTYPE_BINARY have variable bounds

Parameters
scipSCIP data structure
varset variable
varidxfor lower bound set variable index, for upper bound set variable index
  • number of variables
posvariables's position in bdchinfos
nredvarsnumber of reduced variables so far
boundsarray of bounds where one of them must be fullfilled
boundtypesarray of bound types
newboundsarray of implied bounds(, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
countsarray of number of implication on a bound (, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
countnonzerosarray to store the indices of non-zero entries in the counts array
ncountnonzerospointer to store the number of non-zero entries in the counts array
issetvararray containing for set variables the position in the current set, or 0 if it is not a set variable or -1, if it is a redundant(i.e. implies another set variable) set variables(, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
nvarsnumber of problem variables
foundbinpointer to store the lowest index of a binary implication variable when found
foundnonbinpointer to store the lowest index of a non-binary implication variable when found
implidxarray to store the variable indices (for upper bound 'nvars' is added to the index) which are implied
nimplidxpointer to store the number of implied variables
lastboundsarray to remember last implied bounds before taken the current variable into account, first nvars for lower bound, second nvars for upper bound

this array is used when a set variable got redundant, because it implies another set variable, and we need to correct the counts array

Definition at line 40 of file presolve.c.

References MIN, NULL, SCIP_INVALID, SCIP_Real, SCIP_VARTYPE_BINARY, SCIPdebugMessage, SCIPisFeasEQ(), SCIPisFeasGT(), SCIPisFeasLT(), SCIPisZero(), SCIPvarGetLbGlobal(), SCIPvarGetName(), SCIPvarGetNVlbs(), SCIPvarGetNVubs(), SCIPvarGetProbindex(), SCIPvarGetType(), SCIPvarGetUbGlobal(), SCIPvarGetVlbCoefs(), SCIPvarGetVlbConstants(), SCIPvarGetVlbVars(), SCIPvarGetVubCoefs(), SCIPvarGetVubConstants(), SCIPvarGetVubVars(), and SCIPvarIsBinary().

Referenced by SCIPshrinkDisjunctiveVarSet().

static void collectNonBinaryImplicationData ( SCIP scip,
SCIP_VAR var,
int  varidx,
int  pos,
int  nredvars,
SCIP_Bool  value,
SCIP_Real bounds,
SCIP_Bool boundtypes,
SCIP_Real newbounds,
int *  counts,
int *  countnonzeros,
int *  ncountnonzeros,
int *  issetvar,
int  nvars,
int *  foundbin,
int *  foundnonbin,
int *  implidx,
int *  nimplidx,
SCIP_Real lastbounds 
)
static

collect non-binary implication data for variable set reduction and global bound implications; only variable which have the vartype SCIP_VARTYPE_BINARY have implications, otherwise the implications are saved as variable bounds

Parameters
scipSCIP data structure
varset variable
varidxfor lower bound set variable index, for upper bound set variable index + number of variables
posvariables's position in bdchinfos
nredvarsnumber of reduced variables so far
valuevalue used for clique and implication info
boundsarray of bounds where one of them must be fullfilled
boundtypesarray of bound types
newboundsarray of implied bounds(, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
countsarray of number of implication on a bound (, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
countnonzerosarray to store the indices of non-zero entries in the counts array
ncountnonzerospointer to store the number of non-zero entries in the counts array
issetvararray containing for set variables the position in the current set, or 0 if it is not a set variable or -1, if it is a redundant(i.e. implies another set variable) set variables(, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
nvarsnumber of problem variables
foundbinpointer to store the lowest index of a binary implication variable when found
foundnonbinpointer to store the lowest index of a non-binary implication variable when found
implidxarray to store the variable indices (for upper bound 'nvars' is added to the index) which are implied
nimplidxpointer to store the number of implied variables
lastboundsarray to remember last implied bounds before taken the current variable into account, first nvars for lower bound, second nvars for upper bound

this array is used when a set variable got redundant, because it implies another set variable, and we need to correct the counts array

Definition at line 563 of file presolve.c.

References MIN, NULL, SCIP_BOUNDTYPE_UPPER, SCIP_INVALID, SCIP_Real, SCIP_VARTYPE_BINARY, SCIPdebugMessage, SCIPisFeasEQ(), SCIPisFeasGE(), SCIPisFeasLE(), SCIPvarGetImplBounds(), SCIPvarGetImplTypes(), SCIPvarGetImplVars(), SCIPvarGetLbGlobal(), SCIPvarGetName(), SCIPvarGetNImpls(), SCIPvarGetProbindex(), SCIPvarGetType(), SCIPvarGetUbGlobal(), and SCIPvarIsBinary().

Referenced by SCIPshrinkDisjunctiveVarSet().

static void collectBinaryCliqueData ( SCIP_VAR var,
int  varidx,
int  pos,
int  nredvars,
SCIP_Bool  value,
SCIP_Real bounds,
SCIP_Bool boundtypes,
SCIP_Real newbounds,
int *  counts,
int *  countnonzeros,
int *  ncountnonzeros,
int *  issetvar,
int  nvars,
int *  foundbin,
int *  implidx,
int *  nimplidx 
)
static

collect clique data on binary variables for variable set reduction and global bound implications

Parameters
varset variable
varidxfor lower bound set variable index, for upper bound set variable index
  • number of variables
posvariables's position in bdchinfos
nredvarsnumber of reduced variables so far
valuevalue used for clique and implication info
boundsarray of bounds where one of them must be fullfilled
boundtypesarray of bound types
newboundsarray of implied bounds(, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
countsarray of number of implication on a bound (, size is two times number of variables, first half for implied lower bounds, second for implied upper bounds)
countnonzerosarray to store the indices of non-zero entries in the counts array
ncountnonzerospointer to store the number of non-zero entries in the counts array
issetvararray containing for set variables the position in the current set, or 0 if it is not a set variable, or -1, if it is a redundant (i.e. implies another set variable) set variable (the size of the array is two times the number of variables, first half for implied lower bounds, second for implied upper bounds)
nvarsnumber of problem variables
foundbinpointer to store the lowest index of a binary implication variable when found
implidxarray to store the variable indices (for upper bound 'nvars' is added to the index) which are implied
nimplidxpointer to store the number of implied variables

Definition at line 791 of file presolve.c.

References MIN, NULL, SCIP_Bool, SCIPcliqueGetNVars(), SCIPcliqueGetValues(), SCIPcliqueGetVars(), SCIPdebugMessage, SCIPvarGetCliques(), SCIPvarGetLbGlobal(), SCIPvarGetName(), SCIPvarGetNCliques(), SCIPvarGetProbindex(), SCIPvarGetUbGlobal(), and SCIPvarIsBinary().

Referenced by SCIPshrinkDisjunctiveVarSet().

SCIP_RETCODE SCIPshrinkDisjunctiveVarSet ( SCIP scip,
SCIP_VAR **  vars,
SCIP_Real bounds,
SCIP_Bool boundtypes,
SCIP_Bool redundants,
int  nvars,
int *  nredvars,
int *  nglobalred,
SCIP_Bool setredundant,
SCIP_Bool glbinfeas,
SCIP_Bool  fullshortening 
)

try to reduce the necessary variable in a set of variables with corresponding bounds and boundtypes for which one must be fulfilled

e.g. a set of logicor or bounddisjunctive constraint variables would be such a set

consider the following set:

x1 >= 1, x2 >= 3, x3 >= 1, x4 <= 0

by (global) implication data (cliques, implications, and variable bounds) we have also the following implications given:

x1 >= 1 => x3 >= 1 x2 >= 2 => x3 >= 1 x4 <= 0 => x1 >= 1

Because of the last implication x4 is redundant, because x1 >= 1 would also be fulfilled in the variable set, so we can reduce the set by x4. Also, the both other implications and x3 >= 1 (in the given variable set) all imply exactly x3 >= 1, so we tighten the global lower bound of x3 to 1 and the set of variables gets redundant.

Parameters
scipSCIP data structure
varsvariables array for which at least one must be fulfilled in the following bounds and boundtypes
boundsbounds array for which at least one must be fulfilled
boundtypesboundtypes array (TRUE == SCIP_BOUNDTYPE_UPPER, FALSE == SCIP_BOUNDTYPE_LOWER) for which at least one must be fulfilled
redundantsarray which be filled and then indicate if a variable in the set is redundant
nvarsnumber of variables
nredvarspointer to store how many variables can be removed
nglobalredpointer to store number of global reductions on variable bounds found through this set of variables
setredundantpointer to store if we found a global reduction on a variable which was part of the given set of variables, this makes this disjunction redundant
glbinfeaspointer to store if global infeasibility was detected
fullshorteningdo we want to try the shortening procedure over the whole set (which might be expensive)

Definition at line 953 of file presolve.c.

References BMSclearMemoryArray, Scip::branchcand, CLEARRATIO, Scip::cliquetable, collectBinaryCliqueData(), collectNonBinaryImplicationData(), collectNonBinaryVBoundData(), Scip::eventqueue, FALSE, Scip::lp, Scip::mem, SCIP_Tree::npendingbdchgs, NULL, Scip::origprob, SCIP_Mem::probmem, Scip::reopt, SCIP_Tree::root, SCIP_Bool, SCIP_BOUNDTYPE_LOWER, SCIP_BOUNDTYPE_UPPER, SCIP_CALL, SCIP_INVALID, SCIP_OKAY, SCIP_Real, SCIP_VARTYPE_BINARY, SCIPallocBufferArray, SCIPallocCleanBufferArray, SCIPcleanupCliques(), SCIPcutoffNode(), SCIPdebugMessage, SCIPfreeBufferArray, SCIPfreeCleanBufferArray, SCIPgetRootNode(), SCIPisGT(), SCIPisLT(), SCIPnodeAddBoundchg(), SCIPprobGetName(), SCIPprobGetNImplBinVars(), SCIPprobGetNVars(), SCIPprobGetVars(), SCIPvarGetLbGlobal(), SCIPvarGetName(), SCIPvarGetProbindex(), SCIPvarGetType(), SCIPvarGetUbGlobal(), SCIPvarIsBinary(), Scip::set, Scip::stat, Scip::transprob, Scip::tree, and TRUE.

Referenced by detectImpliedBounds(), and shortenConss().