/** returns a variable, that pushes activity of the row in the given direction with minimal negative impact on other rows;
* if variables have equal impact, chooses the one with best objective value improvement in corresponding direction;
* rounding in a direction is forbidden, if this forces the objective value over the upper bound
*/
static
SCIP_RETCODE selectRounding(
SCIP* scip, /**< SCIP data structure */
SCIP_SOL* sol, /**< primal solution */
SCIP_Real minobj, /**< minimal objective value possible after rounding remaining fractional vars */
SCIP_ROW* row, /**< LP row */
int direction, /**< should the activity be increased (+1) or decreased (-1)? */
SCIP_VAR** roundvar, /**< pointer to store the rounding variable, returns NULL if impossible */
SCIP_Real* oldsolval, /**< pointer to store old (fractional) solution value of rounding variable */
SCIP_Real* newsolval /**< pointer to store new (rounded) solution value of rounding variable */
)
{
SCIP_COL* col;
SCIP_VAR* var;
SCIP_Real val;
SCIP_COL** rowcols;
SCIP_Real* rowvals;
SCIP_Real solval;
SCIP_Real roundval;
SCIP_Real obj;
SCIP_Real deltaobj;
SCIP_Real bestdeltaobj;
SCIP_VARTYPE vartype;
int nrowcols;
int nlocks;
int minnlocks;
int c;
assert(direction == +1 || direction == -1);
assert(roundvar != NULL);
assert(oldsolval != NULL);
assert(newsolval != NULL);
/* get row entries */
rowcols = SCIProwGetCols(row);
rowvals = SCIProwGetVals(row);
nrowcols = SCIProwGetNLPNonz(row);
/* select rounding variable */
minnlocks = INT_MAX;
bestdeltaobj = SCIPinfinity(scip);
*roundvar = NULL;
for( c = 0; c < nrowcols; ++c )
{
col = rowcols[c];
var = SCIPcolGetVar(col);
vartype = SCIPvarGetType(var);
if( vartype == SCIP_VARTYPE_BINARY || vartype == SCIP_VARTYPE_INTEGER )
{
solval = SCIPgetSolVal(scip, sol, var);
if( !SCIPisFeasIntegral(scip, solval) )
{
val = rowvals[c];
obj = SCIPvarGetObj(var);
if( direction * val < 0.0 )
{
/* rounding down */
nlocks = SCIPvarGetNLocksDown(var);
if( nlocks <= minnlocks )
{
roundval = SCIPfeasFloor(scip, solval);
deltaobj = obj * (roundval - solval);
if( (nlocks < minnlocks || deltaobj < bestdeltaobj) && minobj - obj < SCIPgetCutoffbound(scip) )
{
minnlocks = nlocks;
bestdeltaobj = deltaobj;
*roundvar = var;
*oldsolval = solval;
*newsolval = roundval;
}
}
}
else
{
/* rounding up */
assert(direction * val > 0.0);
nlocks = SCIPvarGetNLocksUp(var);
if( nlocks <= minnlocks )
{
roundval = SCIPfeasCeil(scip, solval);
deltaobj = obj * (roundval - solval);
if( (nlocks < minnlocks || deltaobj < bestdeltaobj) && minobj + obj < SCIPgetCutoffbound(scip) )
{
minnlocks = nlocks;
bestdeltaobj = deltaobj;
*roundvar = var;
*oldsolval = solval;
*newsolval = roundval;
}
}
}
}
}
}
return SCIP_OKAY;
}
/** returns a variable, that pushes activity of the row in the given direction with minimal negative impact on other rows;
* if variables have equal impact, chooses the one with best objective value improvement in corresponding direction;
* prefer fractional integers over other variables in order to become integral during the process;
* shifting in a direction is forbidden, if this forces the objective value over the upper bound, or if the variable
* was already shifted in the opposite direction
*/
static
SCIP_RETCODE selectShifting(
SCIP* scip, /**< SCIP data structure */
SCIP_SOL* sol, /**< primal solution */
SCIP_ROW* row, /**< LP row */
SCIP_Real rowactivity, /**< activity of LP row */
int direction, /**< should the activity be increased (+1) or decreased (-1)? */
SCIP_Real* nincreases, /**< array with weighted number of increasings per variables */
SCIP_Real* ndecreases, /**< array with weighted number of decreasings per variables */
SCIP_Real increaseweight, /**< current weight of increase/decrease updates */
SCIP_VAR** shiftvar, /**< pointer to store the shifting variable, returns NULL if impossible */
SCIP_Real* oldsolval, /**< pointer to store old solution value of shifting variable */
SCIP_Real* newsolval /**< pointer to store new (shifted) solution value of shifting variable */
)
{
SCIP_COL** rowcols;
SCIP_Real* rowvals;
int nrowcols;
SCIP_Real activitydelta;
SCIP_Real bestshiftscore;
SCIP_Real bestdeltaobj;
int c;
assert(direction == +1 || direction == -1);
assert(nincreases != NULL);
assert(ndecreases != NULL);
assert(shiftvar != NULL);
assert(oldsolval != NULL);
assert(newsolval != NULL);
/* get row entries */
rowcols = SCIProwGetCols(row);
rowvals = SCIProwGetVals(row);
nrowcols = SCIProwGetNLPNonz(row);
/* calculate how much the activity must be shifted in order to become feasible */
activitydelta = (direction == +1 ? SCIProwGetLhs(row) - rowactivity : SCIProwGetRhs(row) - rowactivity);
assert((direction == +1 && SCIPisPositive(scip, activitydelta))
|| (direction == -1 && SCIPisNegative(scip, activitydelta)));
/* select shifting variable */
bestshiftscore = SCIP_REAL_MAX;
bestdeltaobj = SCIPinfinity(scip);
*shiftvar = NULL;
*newsolval = 0.0;
*oldsolval = 0.0;
for( c = 0; c < nrowcols; ++c )
{
SCIP_COL* col;
SCIP_VAR* var;
SCIP_Real val;
SCIP_Real solval;
SCIP_Real shiftval;
SCIP_Real shiftscore;
SCIP_Bool isinteger;
SCIP_Bool isfrac;
SCIP_Bool increase;
col = rowcols[c];
var = SCIPcolGetVar(col);
val = rowvals[c];
assert(!SCIPisZero(scip, val));
solval = SCIPgetSolVal(scip, sol, var);
isinteger = (SCIPvarGetType(var) == SCIP_VARTYPE_BINARY || SCIPvarGetType(var) == SCIP_VARTYPE_INTEGER);
isfrac = isinteger && !SCIPisFeasIntegral(scip, solval);
increase = (direction * val > 0.0);
/* calculate the score of the shifting (prefer smaller values) */
if( isfrac )
shiftscore = increase ? -1.0 / (SCIPvarGetNLocksUp(var) + 1.0) :
-1.0 / (SCIPvarGetNLocksDown(var) + 1.0);
else
{
int probindex;
probindex = SCIPvarGetProbindex(var);
if( increase )
shiftscore = ndecreases[probindex]/increaseweight;
else
shiftscore = nincreases[probindex]/increaseweight;
if( isinteger )
shiftscore += 1.0;
}
if( shiftscore <= bestshiftscore )
{
SCIP_Real deltaobj;
if( !increase )
{
/* shifting down */
assert(direction * val < 0.0);
if( isfrac )
shiftval = SCIPfeasFloor(scip, solval);
else
{
SCIP_Real lb;
assert(activitydelta/val < 0.0);
shiftval = solval + activitydelta/val;
assert(shiftval <= solval); /* may be equal due to numerical digit erasement in the subtraction */
if( SCIPvarIsIntegral(var) )
shiftval = SCIPfeasFloor(scip, shiftval);
lb = SCIPvarGetLbGlobal(var);
shiftval = MAX(shiftval, lb);
}
}
else
{
/* shifting up */
assert(direction * val > 0.0);
if( isfrac )
shiftval = SCIPfeasCeil(scip, solval);
else
{
SCIP_Real ub;
assert(activitydelta/val > 0.0);
shiftval = solval + activitydelta/val;
assert(shiftval >= solval); /* may be equal due to numerical digit erasement in the subtraction */
if( SCIPvarIsIntegral(var) )
shiftval = SCIPfeasCeil(scip, shiftval);
ub = SCIPvarGetUbGlobal(var);
shiftval = MIN(shiftval, ub);
}
}
if( SCIPisEQ(scip, shiftval, solval) )
continue;
deltaobj = SCIPvarGetObj(var) * (shiftval - solval);
if( shiftscore < bestshiftscore || deltaobj < bestdeltaobj )
{
bestshiftscore = shiftscore;
bestdeltaobj = deltaobj;
*shiftvar = var;
*oldsolval = solval;
*newsolval = shiftval;
}
}
}
return SCIP_OKAY;
}
