[Cbc] Unusually slow time taken at a node of branch-and-bound tree

[Aleksandr M. Kazachkov]

Hello all,

On my computer, Cbc-2.9 (latest stable, compiled with lapack, blas, and
enable_debug on) takes an unusually long time (~15 minutes) on a particular
node of the branch-and-bound tree for a version of the instance pigeon-13
from MIPLIB (after applying some preprocessing to it). The instance is here:

https://drive.google.com/file/d/17CWEN1A5ZefhAEZsUwnU1gJl_EPM9d5b/view?usp=sharing

I am reporting this in case the behavior is the result of a bug, though it
may simply be a case in which I should be using different settings. On my
system, the following lines of code reproduce the behavior:

OsiClpSolverInterface* solver = new OsiClpSolverInterface;
solver->readMps("pigeon-13_presolved.mps.gz");
CbcModel* cbc_model = new CbcModel;
cbc_model->swapSolver(solver);
cbc_model->setModelOwnsSolver(true); // solver will be deleted with cbc
object
cbc_model->setLogLevel(3);
cbc_model->messagesPointer()->setDetailMessages(10, 10000, (int *) NULL);
cbc_model->setPrintFrequency(1);
cbc_model->setMaximumNodes(656); // at least on my system, this will show
the slow node
cbc_model->branchAndBound(3);

As indicated in the log (excerpt below), Cbc stalls for quite a while after
654 nodes.

Cbc0010I After 654 nodes, 44 on tree, 1e+50 best solution, best possible
-13000 (84.18 seconds)
Clp0006I 0 Obj -13000 Primal inf 0.1871137 (1)
Clp0006I 2 Obj -13000
Clp0000I Optimal - objective value -13000
---- long stall here ---
Cbc0007I Strong branching on 145 (184), down 0 (20) up 6.4595608e+14 (19)
value 0.5
Cbc0007I Strong branching on 179 (218), down 3.6850268e+13 (12) up 0 (20)
value 0.5
Node 655 depth 45 unsatisfied 22 sum 1.40366e+15 obj -13000 guess -12708
branching on 184
Cbc0015I Node 655 Obj -13000 Unsat 22 depth 45
Cbc0010I After 655 nodes, 44 on tree, 1e+50 best solution, best possible
-13000 (1015.90 seconds)
Clp0006I 0 Obj -13000 Primal inf 0.10206197 (1)
Clp0006I 5 Obj -13000
Clp0000I Optimal - objective value -13000

If there is any other information that would be helpful that I can provide,
please let me know,
Aleksandr Kazachkov
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