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presol_boundshift.c
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/
presol_boundshift.c
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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/* */
/* This file is part of the program and library */
/* SCIP --- Solving Constraint Integer Programs */
/* */
/* Copyright (C) 2002-2014 Konrad-Zuse-Zentrum */
/* fuer Informationstechnik Berlin */
/* */
/* SCIP is distributed under the terms of the ZIB Academic License. */
/* */
/* You should have received a copy of the ZIB Academic License */
/* along with SCIP; see the file COPYING. If not email to scip@zib.de. */
/* */
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/**@file presol_boundshift.c
* @brief presolver that converts variables with domain [a,b] to variables with domain [0,b-a]
* @author Stefan Heinz
* @author Michael Winkler
*/
/**@todo test this presolving step to decide whether to turn it in default mode on or off */
/*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/
#include <assert.h>
#include <string.h>
#include "scip/presol_boundshift.h"
#define PRESOL_NAME "boundshift"
#define PRESOL_DESC "converts variables with domain [a,b] to variables with domain [0,b-a]"
#define PRESOL_PRIORITY 7900000 /**< priority of the presolver (>= 0: before, < 0: after constraint handlers) */
#define PRESOL_MAXROUNDS 0 /**< maximal number of presolving rounds the presolver participates in (-1: no limit) */
#define PRESOL_DELAY FALSE /**< should presolver be delayed, if other presolvers found reductions? */
/*
* Default parameter settings
*/
#define DEFAULT_MAXSHIFT SCIP_LONGINT_MAX /**< absolute value of maximum shift */
#define DEFAULT_FLIPPING TRUE /**< is flipping allowed? */
#define DEFAULT_INTEGER TRUE /**< are only integer ranges shifted */
/*
* Data structures
*/
/** presolver data */
struct SCIP_PresolData
{
SCIP_Longint maxshift; /**< absolute value of maximum shift */
SCIP_Bool flipping; /**< is flipping allowed? */
SCIP_Bool integer; /**< shift only integer values? */
};
/*
* Local methods
*/
/** initializes the presolver data */
static
void initPresoldata(
SCIP_PRESOLDATA* presoldata /**< presolver data */
)
{
assert(presoldata != NULL);
presoldata->maxshift = DEFAULT_MAXSHIFT;
presoldata->flipping = DEFAULT_FLIPPING;
presoldata->integer = DEFAULT_INTEGER;
}
/*
* Callback methods of presolver
*/
/** copy method for constraint handler plugins (called when SCIP copies plugins) */
static
SCIP_DECL_PRESOLCOPY(presolCopyBoundshift)
{ /*lint --e{715}*/
assert(scip != NULL);
assert(presol != NULL);
assert(strcmp(SCIPpresolGetName(presol), PRESOL_NAME) == 0);
/* call inclusion method of presolver */
SCIP_CALL( SCIPincludePresolBoundshift(scip) );
return SCIP_OKAY;
}
/** destructor of presolver to free user data (called when SCIP is exiting) */
static
SCIP_DECL_PRESOLFREE(presolFreeBoundshift)
{ /*lint --e{715}*/
SCIP_PRESOLDATA* presoldata;
/* free presolver data */
presoldata = SCIPpresolGetData(presol);
assert(presoldata != NULL);
SCIPfreeMemory(scip, &presoldata);
SCIPpresolSetData(presol, NULL);
return SCIP_OKAY;
}
/** presolving execution method */
static
SCIP_DECL_PRESOLEXEC(presolExecBoundshift)
{ /*lint --e{715}*/
SCIP_PRESOLDATA* presoldata;
SCIP_VAR** scipvars;
SCIP_VAR** vars;
int nbinvars;
int nvars;
int v;
assert(scip != NULL);
assert(presol != NULL);
assert(strcmp(SCIPpresolGetName(presol), PRESOL_NAME) == 0);
assert(result != NULL);
*result = SCIP_DIDNOTRUN;
/* get presolver data */
presoldata = SCIPpresolGetData(presol);
assert(presoldata != NULL);
/* get the problem variables */
scipvars = SCIPgetVars(scip);
nbinvars = SCIPgetNBinVars(scip);
nvars = SCIPgetNVars(scip) - nbinvars;
if( nvars == 0 )
return SCIP_OKAY;
if( SCIPdoNotAggr(scip) )
return SCIP_OKAY;
*result = SCIP_DIDNOTFIND;
/* copy the integer variables into an own array, since adding new integer variables affects the left-most slots in
* the array and thereby interferes with our search loop
*/
SCIP_CALL( SCIPduplicateBufferArray(scip, &vars, &scipvars[nbinvars], nvars) );
/* scan the integer, implicit, and continuous variables for possible conversion */
for( v = nvars - 1; v >= 0; --v )
{
SCIP_VAR* var = vars[v];
SCIP_Real lb;
SCIP_Real ub;
assert(SCIPvarGetType(var) != SCIP_VARTYPE_BINARY);
/* get current variable's bounds */
lb = SCIPvarGetLbGlobal(var);
ub = SCIPvarGetUbGlobal(var);
assert( SCIPisLE(scip, lb, ub) );
if( SCIPisEQ(scip, lb, ub) )
continue;
if( presoldata->integer && !SCIPisIntegral(scip, ub - lb) )
continue;
/* check if bounds are shiftable */
if( !SCIPisEQ(scip, lb, 0.0) && /* lower bound != 0.0 */
SCIPisLT(scip, ub, SCIPinfinity(scip)) && /* upper bound != infinity */
SCIPisGT(scip, lb, -SCIPinfinity(scip)) && /* lower bound != -infinity */
#if 0
SCIPisLT(scip, ub - lb, SCIPinfinity(scip)) && /* interval length less than SCIPinfinity(scip) */
#endif
SCIPisLT(scip, ub - lb, (SCIP_Real) presoldata->maxshift) ) /* less than max shifting */
{
SCIP_VAR* newvar;
char newvarname[SCIP_MAXSTRLEN];
SCIP_Bool infeasible;
SCIP_Bool redundant;
SCIP_Bool aggregated;
SCIPdebugMessage("convert range <%s>[%g,%g] to [%g,%g]\n", SCIPvarGetName(var), lb, ub, 0.0, (ub - lb) );
/* create new variable */
(void) SCIPsnprintf(newvarname, SCIP_MAXSTRLEN, "%s_shift", SCIPvarGetName(var));
SCIP_CALL( SCIPcreateVar(scip, &newvar, newvarname, 0.0, (ub - lb), 0.0, SCIPvarGetType(var),
SCIPvarIsInitial(var), SCIPvarIsRemovable(var), NULL, NULL, NULL, NULL, NULL) );
SCIP_CALL( SCIPaddVar(scip, newvar) );
/* aggregate old variable with new variable */
if( presoldata->flipping )
{
if( REALABS(ub) < REALABS(lb) )
{
SCIP_CALL( SCIPaggregateVars(scip, var, newvar, 1.0, 1.0, ub, &infeasible, &redundant, &aggregated) );
}
else
{
SCIP_CALL( SCIPaggregateVars(scip, var, newvar, 1.0, -1.0, lb, &infeasible, &redundant, &aggregated) );
}
}
else
{
SCIP_CALL( SCIPaggregateVars(scip, var, newvar, 1.0, -1.0, lb, &infeasible, &redundant, &aggregated) );
}
assert(!infeasible);
assert(redundant);
assert(aggregated);
SCIPdebugMessage("var <%s> with bounds [%f,%f] has obj %f\n",
SCIPvarGetName(newvar),SCIPvarGetLbGlobal(newvar),SCIPvarGetUbGlobal(newvar),SCIPvarGetObj(newvar));
/* release variable */
SCIP_CALL( SCIPreleaseVar(scip, &newvar) );
/* take care of statistic */
(*naggrvars)++;
*result = SCIP_SUCCESS;
}
}
/* free temporary memory */
SCIPfreeBufferArray(scip, &vars);
return SCIP_OKAY;
}
/*
* presolver specific interface methods
*/
/** creates the boundshift presolver and includes it in SCIP */
SCIP_RETCODE SCIPincludePresolBoundshift(
SCIP* scip /**< SCIP data structure */
)
{
SCIP_PRESOLDATA* presoldata;
SCIP_PRESOL* presolptr;
/* create boundshift presolver data */
SCIP_CALL( SCIPallocMemory(scip, &presoldata) );
initPresoldata(presoldata);
/* include presolver */
SCIP_CALL( SCIPincludePresolBasic(scip, &presolptr, PRESOL_NAME, PRESOL_DESC, PRESOL_PRIORITY, PRESOL_MAXROUNDS, PRESOL_DELAY,
presolExecBoundshift,
presoldata) );
assert(presolptr != NULL);
SCIP_CALL( SCIPsetPresolCopy(scip, presolptr, presolCopyBoundshift) );
SCIP_CALL( SCIPsetPresolFree(scip, presolptr, presolFreeBoundshift) );
/* add probing presolver parameters */
SCIP_CALL( SCIPaddLongintParam(scip,
"presolving/boundshift/maxshift",
"absolute value of maximum shift",
&presoldata->maxshift, TRUE, DEFAULT_MAXSHIFT, 0LL, SCIP_LONGINT_MAX, NULL, NULL) );
SCIP_CALL( SCIPaddBoolParam(scip,
"presolving/boundshift/flipping",
"is flipping allowed (multiplying with -1)?",
&presoldata->flipping, TRUE, DEFAULT_FLIPPING, NULL, NULL) );
SCIP_CALL( SCIPaddBoolParam(scip,
"presolving/boundshift/integer",
"shift only integer ranges?",
&presoldata->integer, TRUE, DEFAULT_INTEGER, NULL, NULL) );
return SCIP_OKAY;
}