def test_initialize_queue(self):
node_limit = None
time_limit = None
log = get_simple_logger()
log_interval_seconds = inf
log_new_incumbent = True
convergence_checker = ConvergenceChecker(minimize)
root = Node(size=0)
Node._insert_tree_id(root._data, 0)
root.bound = convergence_checker.unbounded_objective
root.objective = convergence_checker.infeasible_objective
queue = DispatcherQueueData(nodes=[root], next_tree_id=1)
disp = DispatcherLocal()
disp.initialize(0, queue, 'bound', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert disp.best_objective == 0
disp.initialize(1, queue, 'bound', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert disp.best_objective == 1
root.objective = -1
disp.initialize(1, queue, 'bound', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert disp.best_objective == -1
def _add_work_to_queue(self, node_data, set_tree_id=True):
if set_tree_id:
assert not Node._has_tree_id(node_data)
Node._insert_tree_id(node_data, self.next_tree_id)
self.next_tree_id += 1
else:
assert Node._has_tree_id(node_data)
assert Node._extract_tree_id(node_data) < self.next_tree_id
bound = Node._extract_bound(node_data)
if self.converger.eligible_for_queue(bound, self.best_objective):
self.queue.put(node_data)
return True
else:
self._check_update_worst_terminal_bound(bound)
return False
def test_tree_id(self):
node = Node()
assert node.tree_id is None
assert node.parent_tree_id is None
Node._insert_tree_id(node._data, 1)
assert node.tree_id == 1
assert node.parent_tree_id is None
Node._insert_parent_tree_id(node._data, 2)
assert node.tree_id == 1
assert node.parent_tree_id == 2
Node._clear_tree_id(node._data)
assert node.tree_id is None
assert node.parent_tree_id == 2
Node._clear_parent_tree_id(node._data)
assert node.tree_id is None
assert node.parent_tree_id is None
def test_queue_strategy(self):
node_limit = None
time_limit = None
log = get_simple_logger()
log_interval_seconds = inf
log_new_incumbent = True
convergence_checker = ConvergenceChecker(minimize)
root = Node(size=0)
Node._insert_tree_id(root._data, 0)
root.bound = convergence_checker.unbounded_objective
root.objective = convergence_checker.infeasible_objective
queue = DispatcherQueueData(nodes=[root], next_tree_id=1)
disp = DispatcherLocal()
disp.initialize(inf, queue, 'bound', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is WorstBoundFirstPriorityQueue
disp.initialize(inf, queue, 'custom', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is CustomPriorityQueue
disp.initialize(inf, queue, 'objective', convergence_checker,
node_limit, time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is BestObjectiveFirstPriorityQueue
disp.initialize(inf, queue, 'breadth', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is BreadthFirstPriorityQueue
disp.initialize(inf, queue, 'depth', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is DepthFirstPriorityQueue
disp.initialize(inf, queue, 'fifo', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is FIFOQueue
disp.initialize(inf, queue, 'random', convergence_checker, node_limit,
time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is RandomPriorityQueue
disp.initialize(inf, queue, 'local_gap', convergence_checker,
node_limit, time_limit, log, log_interval_seconds,
log_new_incumbent)
assert type(disp.queue) is LocalGapPriorityQueue
def _logging_check(comm):
opt = Solver(comm=comm)
p = DummyProblem()
if opt.is_dispatcher:
assert (comm is None) or (comm.rank == 0)
root = Node()
p.save_state(root)
root.objective = p.infeasible_objective()
root.bound = p.unbounded_objective()
assert root.tree_id is None
Node._insert_tree_id(root._data, 0)
initialize_queue = DispatcherQueueData(nodes=[root], next_tree_id=1)
out = StringIO()
formatter = logging.Formatter("[%(levelname)s] %(message)s")
opt._disp.initialize(
p.infeasible_objective(), initialize_queue, "bound",
ConvergenceChecker(p.sense()), None, None,
get_simple_logger(console=True,
stream=out,
level=logging.DEBUG,
formatter=formatter), 0.0, True)
opt._disp.log_debug("0: debug")
opt._disp.log_info("0: info")
opt._disp.log_warning("0: warning")
opt._disp.log_error("0: error")
if (comm is not None) and (comm.size > 1):
opt._disp.serve()
else:
assert comm is not None
if comm.size > 1:
for i in range(1, comm.size):
if comm.rank == i:
opt._disp.log_debug(str(comm.rank) + ": debug")
opt._disp.log_info(str(comm.rank) + ": info")
opt._disp.log_warning(str(comm.rank) + ": warning")
opt._disp.log_error(str(comm.rank) + ": error")
opt.worker_comm.Barrier()
if opt.worker_comm.rank == 0:
opt._disp.stop_listen()
if comm is not None:
comm.Barrier()
if opt.is_dispatcher:
assert ('\n'.join(out.getvalue().splitlines()[8:])) == \
_get_logging_baseline(comm.size if comm is not None else 1)
def test_children(self):
parent = Node()
assert parent.queue_priority is None
assert parent.tree_id is None
assert parent.parent_tree_id is None
assert parent.tree_depth == 0
assert len(parent.state) == 0
parent.queue_priority = 10
assert parent.queue_priority == 10
assert parent.tree_id is None
assert parent.parent_tree_id is None
assert parent.tree_depth == 0
assert len(parent.state) == 0
parent.bound = -1
assert parent.queue_priority == 10
assert parent.tree_id is None
assert parent.parent_tree_id is None
assert parent.tree_depth == 0
assert parent.bound == -1
parent.objective = -2
assert parent.queue_priority == 10
assert parent.tree_id is None
assert parent.parent_tree_id is None
assert parent.tree_depth == 0
assert parent.bound == -1
assert parent.objective == -2
assert len(parent.state) == 0
parent.resize(5)
assert parent.queue_priority == 10
assert parent.tree_id is None
assert parent.parent_tree_id is None
assert parent.tree_depth == 0
assert parent.bound == -1
assert parent.objective == -2
assert len(parent.state) == 5
children = [parent.new_child() for i in range(3)]
assert len(children) == 3
for child in children:
assert child.queue_priority is None
assert child.tree_id is None
assert child.parent_tree_id is None
assert child.tree_depth == 1
assert child.bound == -1
assert child.objective == -2
assert len(child.state) == 5
Node._insert_tree_id(parent._data, 0)
assert parent.tree_id == 0
children = [parent.new_child() for i in range(3)]
assert len(children) == 3
for child in children:
assert child.queue_priority is None
assert child.tree_id is None
assert child.parent_tree_id == 0
assert child.tree_depth == 1
assert child.bound == -1
assert child.objective == -2
assert len(child.state) == 5
children = [parent.new_child(size=10) for i in range(4)]
assert len(children) == 4
for child in children:
assert child.queue_priority is None
assert child.tree_id is None
assert child.parent_tree_id == 0
assert child.tree_depth == 1
assert child.bound == -1
assert child.objective == -2
assert len(child.state) == 10
def solve(self,
problem,
best_objective=None,
disable_objective_call=False,
absolute_gap=1e-8,
relative_gap=1e-4,
scale_function=_default_scale,
queue_tolerance=0,
branch_tolerance=0,
comparison_tolerance=0,
objective_stop=None,
bound_stop=None,
node_limit=None,
time_limit=None,
initialize_queue=None,
queue_strategy="bound",
log_interval_seconds=1.0,
log_new_incumbent=True,
log=_notset):
"""Solve a problem using branch-and-bound.
Note
----
Parameters for this function are treated differently
depending on whether the process is a worker or
dispatcher. For the serial case (no MPI), the single
process is both a worker and a dispatcher. For the
parallel case, exactly one process is a dispatcher
and all processes are workers. A **(W)** in the
parameter description indicates that it is only used
by worker processes (ignored otherwise). A **(D)**
in the parameter description indicates that it is
only used by the dispatcher process (ignored
otherwise). An **(A)** indicates that it is used by
all processes, and it is assumed the same value is
provided for each process; otherwise, the behavior
is undefined.
Parameters
----------
problem : :class:`pybnb.Problem <pybnb.problem.Problem>`
An object defining a branch-and-bound problem.
best_objective : float, optional
Initializes the solve with an assumed best
objective. This is the only option used by both
worker and dispatcher processes that can be set
to a different value on each process. The
dispatcher will collect all values and use the
best. (default: None)
disable_objective_call : bool, optional
**(W)** Disables requests for an objective value from
subproblems. (default: False)
absolute_gap : float, optional
**(A)** The maximum absolute difference between
the global bound and best objective for the
problem to be considered solved to
optimality. Setting to `None` will disable this
optimality check. (default: 1e-8)
relative_gap : float, optional
**(A)** The maximum relative difference (absolute
difference scaled by `max{1.0,|objective|}`)
between the global bound and best objective for
the problem to be considered solved to
optimality. Setting to `None` will disable this
optimality check. (default: 1e-4)
scale_function : function, optional
**(A)** A function with signature `f(bound,
objective) -> float` that returns a positive
scale factor used to convert the absolute
difference between the bound and objective into
a relative difference. The relative difference
is compared with the `relative_gap` convergence
tolerance to determine if the solver should
terminate. The default is equivalent to
`max{1.0,|objective|}`. Other examples one
could use are `max{|bound|,|objective|}`,
`(|bound|+|objective|)/2`, etc.
queue_tolerance : float, optional
**(A)** The absolute tolerance used when
deciding if a node is eligible to enter the
queue. The difference between the node bound and
the incumbent objective must be greater than
this value. The default setting of zero means
that nodes whose bound is equal to the incumbent
objective are not eligible to enter the
queue. Setting this to larger values can be used
to control the queue size, but it should be kept
small enough to allow absolute and relative
optimality tolerances to be met. This option can
also be set to `None` to allow nodes with a
bound equal to (but not greater than) the
incumbent objective to enter the queue.
(default: 0)
branch_tolerance : float, optional
**(A)** The absolute tolerance used when
deciding if the computed objective and bound for
a node are sufficiently different to branch into
the node. The default value of zero means that
branching will occur if the bound is not exactly
equal to the objective. This option can be set
to `None` to enable branching for nodes with a
bound and objective that are exactly
equal. (default: 0)
comparison_tolerance : float, optional
**(A)** The absolute tolerance used when
deciding if two objective or bound values are
sufficiently different to be considered improved
or worsened. This tolerance controls when the
solver considers a new incumbent objective to be
found. It also controls when warnings are output
about bounds becoming worse on child
nodes. Setting this to larger values can be used
to avoid the above solver actions due to
insignificant numerical differences, but it is
better to deal with these numerical issues by
rounding numbers to a reliable precision before
returning them from the problem methods.
(default: 0)
objective_stop : float, optional
**(A)** If provided, the solve will terminate
when a feasible objective is found that is at
least as good as the specified value, and the
termination_condition flag on the results object
will be set to "objective_limit". If this value
is infinite, the solve will terminate as soon as
a finite objective is found. (default: None)
bound_stop : float, optional
**(A)** If provided, the solve will terminate
when the global bound on the objective is at
least as good as the specified value, and the
termination_condition flag on the results object
will be set to "objective_limit". If this value
is infinite, the solve will terminate as soon as
a finite bound is found. (default: None)
node_limit : int, optional
**(D)** If provided, the solve will begin to
terminate once this many nodes have been served
from the dispatcher queue, and the
termination_condition flag on the results object
will be set to "node_limit". (default: None)
time_limit : float, optional
**(D)** If provided, the solve will begin to
terminate once this amount of time has passed,
and the termination_condition flag on the
results object will be set to "time_limit". Note
that the solve may run for an arbitrarily longer
amount of time, depending how long worker
processes spend completing their final
task. (default: None)
initialize_queue : :class:`pybnb.dispatcher.DispatcherQueueData`, optional
**(D)** Initializes the dispatcher queue with
that remaining from a previous solve (obtained
by calling :func:`Solver.save_dispatcher_queue`
after the solve). If left as None, the queue
will be initialized with a single root node
created by calling :func:`problem.save_state
<pybnb.problem.Problem.save_state>`.
(default: None)
queue_strategy : :class:`QueueStrategy <pybnb.common.QueueStrategy>`
**(D)** Sets the strategy for prioritizing nodes
in the central dispatcher queue. See the
:class:`QueueStrategy
<pybnb.common.QueueStrategy>` enum for the list
of acceptable values. This keyword can be
assigned one of the enumeration attributes or an
equivalent string name. (default: "bound")
log_interval_seconds : float, optional
**(D)** The approximate time (in seconds)
between solver log updates. More time may pass
between log updates if no updates have been
received from worker processes, and less time
may pass if a new incumbent objective is
found. (default: 1.0)
log_new_incumbent : bool
**(D)** Controls whether updates to the best
objective are logged immediately (overriding the
log interval). Setting this to false can be
useful when frequent updates to the incumbent
are expected and the additional logging slows
down the dispatcher. (default: True)
log : logging.Logger, optional
**(D)** A log object where solver output should
be sent. The default value causes all output to
be streamed to the console. Setting to None
disables all output.
Returns
-------
results : :class:`SolverResults`
An object storing information about the solve.
"""
self._reset_local_solve_stats()
self._solve_start = self._time()
assert (initialize_queue is None) or \
(self.is_dispatcher)
if best_objective is None:
best_objective = problem.infeasible_objective()
results = SolverResults()
convergence_checker = ConvergenceChecker(
problem.sense(),
absolute_gap=absolute_gap,
relative_gap=relative_gap,
scale_function=scale_function,
queue_tolerance=queue_tolerance,
branch_tolerance=branch_tolerance,
comparison_tolerance=comparison_tolerance,
objective_stop=objective_stop,
bound_stop=bound_stop)
problem.notify_solve_begins(self.comm,
self.worker_comm,
convergence_checker)
root = Node()
root.queue_priority = 0
problem.save_state(root)
try:
if self.is_dispatcher:
if initialize_queue is None:
root.bound = problem.unbounded_objective()
root.objective = best_objective
assert root.tree_id is None
Node._insert_tree_id(root._data, 0)
initialize_queue = DispatcherQueueData(
nodes=[Node(data_=root._data.copy())],
next_tree_id=1)
if log is _notset:
log = get_simple_logger()
if type(queue_strategy) is \
QueueStrategy:
queue_strategy = \
queue_strategy.value
self._disp.initialize(
best_objective,
initialize_queue,
queue_strategy,
convergence_checker,
node_limit,
time_limit,
log,
log_interval_seconds,
log_new_incumbent)
if not self.is_worker:
def handler(signum, frame): #pragma:nocover
self._disp.log_warning(
"Solve interrupted by user. "
"Waiting for current worker "
"jobs to complete before "
"terminating the solve.")
self._disp.termination_condition = \
TerminationCondition.interrupted
with MPI_InterruptHandler(handler):
tmp = self._disp.serve()
else:
def handler(signum, frame): #pragma:nocover
if self.is_dispatcher:
self._disp.log_warning(
"Solve interrupted by user. "
"Waiting for current worker "
"jobs to complete before "
"terminating the solve.")
self._disp.termination_condition = \
TerminationCondition.interrupted
with MPI_InterruptHandler(handler):
tmp = self._solve(problem,
best_objective,
disable_objective_call,
convergence_checker,
results)
if not self.is_dispatcher:
self._disp.clear_cache()
(results.objective,
results.bound,
results.termination_condition,
self._global_solve_info) = tmp
results.nodes = self._global_solve_info.explored_nodes_count
self._fill_results(results, convergence_checker)
except: #pragma:nocover
sys.stderr.write("Exception caught: "+str(sys.exc_info()[1])+"\n")
sys.stderr.write("Attempting to shut down, but this may hang.\n")
sys.stderr.flush()
raise
finally:
problem.load_state(root)
self._wall_time = self._time() - self._solve_start
results.wall_time = self._wall_time
assert results.solution_status in SolutionStatus,\
str(results)
assert results.termination_condition in TerminationCondition,\
str(results)
problem.notify_solve_finished(self.comm,
self.worker_comm,
results)
if self.is_dispatcher and \
(log is not None) and \
(not log.disabled):
self._disp.log_info("")
if results.solution_status in ("feasible", "optimal"):
agap = convergence_checker.compute_absolute_gap(
results.bound,
results.objective)
rgap = convergence_checker.compute_relative_gap(
results.bound,
results.objective)
if results.solution_status == "feasible":
self._disp.log_info("Feasible solution found")
else:
if (convergence_checker.absolute_gap is not None) and \
agap <= convergence_checker.absolute_gap:
self._disp.log_info("Absolute optimality tolerance met")
if (convergence_checker.relative_gap is not None) and \
rgap <= convergence_checker.relative_gap:
self._disp.log_info("Relative optimality tolerance met")
assert results.solution_status == "optimal"
self._disp.log_info("Optimal solution found!")
elif results.solution_status == "infeasible":
self._disp.log_info("Problem is infeasible")
elif results.solution_status == "unbounded":
self._disp.log_info("Problem is unbounded")
elif results.solution_status == "invalid": #pragma:nocover
self._disp.log_info("Problem is invalid")
else:
assert results.solution_status == "unknown"
self._disp.log_info("Status unknown")
self._disp.log_info("")
self._disp.log_info(str(results))
return results
