/* This is a utility function which does strong branching on
a list of objects and stores the results in OsiHotInfo.objects.
On entry the object sequence is stored in the OsiHotInfo object
and maybe more.
It returns -
-1 - one branch was infeasible both ways
0 - all inspected - nothing can be fixed
1 - all inspected - some can be fixed (returnCriterion==0)
2 - may be returning early - one can be fixed (last one done) (returnCriterion==1)
3 - returning because max time
*/
int
OsiChooseStrong::doStrongBranching( OsiSolverInterface * solver,
OsiBranchingInformation *info,
int numberToDo, int returnCriterion)
{
// Might be faster to extend branch() to return bounds changed
double * saveLower = NULL;
double * saveUpper = NULL;
int numberColumns = solver->getNumCols();
solver->markHotStart();
const double * lower = info->lower_;
const double * upper = info->upper_;
saveLower = CoinCopyOfArray(info->lower_,numberColumns);
saveUpper = CoinCopyOfArray(info->upper_,numberColumns);
numResults_=0;
int returnCode=0;
double timeStart = CoinCpuTime();
for (int iDo=0;iDo<numberToDo;iDo++) {
OsiHotInfo * result = results_ + iDo;
// For now just 2 way
OsiBranchingObject * branch = result->branchingObject();
assert (branch->numberBranches()==2);
/*
Try the first direction. Each subsequent call to branch() performs the
specified branch and advances the branch object state to the next branch
alternative.)
*/
OsiSolverInterface * thisSolver = solver;
if (branch->boundBranch()) {
// ordinary
branch->branch(solver);
// maybe we should check bounds for stupidities here?
solver->solveFromHotStart() ;
} else {
// adding cuts or something
thisSolver = solver->clone();
branch->branch(thisSolver);
// set hot start iterations
int limit;
thisSolver->getIntParam(OsiMaxNumIterationHotStart,limit);
thisSolver->setIntParam(OsiMaxNumIteration,limit);
thisSolver->resolve();
}
// can check if we got solution
// status is 0 finished, 1 infeasible and 2 unfinished and 3 is solution
int status0 = result->updateInformation(thisSolver,info,this);
numberStrongIterations_ += thisSolver->getIterationCount();
if (status0==3) {
// new solution already saved
if (trustStrongForSolution_) {
info->cutoff_ = goodObjectiveValue_;
status0=0;
}
}
if (solver!=thisSolver)
delete thisSolver;
// Restore bounds
for (int j=0;j<numberColumns;j++) {
if (saveLower[j] != lower[j])
solver->setColLower(j,saveLower[j]);
if (saveUpper[j] != upper[j])
solver->setColUpper(j,saveUpper[j]);
}
/*
Try the next direction
*/
thisSolver = solver;
if (branch->boundBranch()) {
// ordinary
branch->branch(solver);
// maybe we should check bounds for stupidities here?
solver->solveFromHotStart() ;
} else {
// adding cuts or something
thisSolver = solver->clone();
branch->branch(thisSolver);
// set hot start iterations
int limit;
thisSolver->getIntParam(OsiMaxNumIterationHotStart,limit);
thisSolver->setIntParam(OsiMaxNumIteration,limit);
thisSolver->resolve();
}
// can check if we got solution
// status is 0 finished, 1 infeasible and 2 unfinished and 3 is solution
int status1 = result->updateInformation(thisSolver,info,this);
numberStrongDone_++;
numberStrongIterations_ += thisSolver->getIterationCount();
if (status1==3) {
// new solution already saved
if (trustStrongForSolution_) {
info->cutoff_ = goodObjectiveValue_;
status1=0;
}
}
if (solver!=thisSolver)
delete thisSolver;
// Restore bounds
for (int j=0;j<numberColumns;j++) {
if (saveLower[j] != lower[j])
solver->setColLower(j,saveLower[j]);
if (saveUpper[j] != upper[j])
solver->setColUpper(j,saveUpper[j]);
}
/*
End of evaluation for this candidate variable. Possibilities are:
* Both sides below cutoff; this variable is a candidate for branching.
* Both sides infeasible or above the objective cutoff: no further action
here. Break from the evaluation loop and assume the node will be purged
by the caller.
* One side below cutoff: Install the branch (i.e., fix the variable). Possibly break
from the evaluation loop and assume the node will be reoptimised by the
caller.
*/
numResults_++;
if (status0==1&&status1==1) {
// infeasible
returnCode=-1;
break; // exit loop
} else if (status0==1||status1==1) {
numberStrongFixed_++;
if (!returnCriterion) {
returnCode=1;
} else {
returnCode=2;
break;
}
}
bool hitMaxTime = ( CoinCpuTime()-timeStart > info->timeRemaining_);
if (hitMaxTime) {
returnCode=3;
break;
}
}
delete [] saveLower;
delete [] saveUpper;
// Delete the snapshot
solver->unmarkHotStart();
return returnCode;
}
