def test_inactive_constraints(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=m.x == 1)
m.c2 = Constraint(expr=m.x == 2)
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
m.c2.deactivate()
self.assertTrue(satisfiable(m))
def test_inactive_constraints(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=m.x == 1)
m.c2 = Constraint(expr=m.x == 2)
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
m.c2.deactivate()
self.assertTrue(satisfiable(m))
def test_8PP_deactive(self):
exfile = import_file(
join(exdir, 'eight_process', 'eight_proc_model.py'))
m = exfile.build_eight_process_flowsheet()
for djn in m.component_data_objects(ctype=Disjunction):
djn.deactivate()
self.assertTrue(satisfiable(m) is not False)
def _prescreen_node(node_data, node_model, solve_data):
config = solve_data.config
# Check node for satisfiability if sat-solver is enabled
if config.check_sat and satisfiable(node_model, config.logger) is False:
if node_data.node_count == 0:
config.logger.info(
"Root node is not satisfiable. Problem is infeasible.")
else:
config.logger.info("SAT solver pruned node %s" %
node_data.node_count)
new_lb = new_ub = float('inf')
else:
# Solve model subproblem
if config.solve_local_rnGDP:
solve_data.config.logger.debug(
"Screening node %s with LB %.10g and %s inactive disjunctions."
% (node_data.node_count, node_data.obj_lb,
node_data.num_unbranched_disjunctions))
new_lb, new_ub = _solve_local_rnGDP_subproblem(
node_model, solve_data)
else:
new_lb, new_ub = float('-inf'), float('inf')
new_lb = max(node_data.obj_lb, new_lb)
new_node_data = node_data._replace(obj_lb=new_lb,
obj_ub=new_ub,
is_screened=True)
return new_node_data
def test_8PP_deactive(self):
exfile = import_file(
join(exdir, 'eight_process', 'eight_proc_model.py'))
m = exfile.build_eight_process_flowsheet()
for djn in m.component_data_objects(ctype=Disjunction):
djn.deactivate()
self.assertTrue(satisfiable(m) is not False)
def test_simple_unsat_model(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=1 == m.x)
m.c2 = Constraint(expr=2 == m.x)
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
def test_simple_unsat_model(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=1 == m.x)
m.c2 = Constraint(expr=2 == m.x)
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
def test_binary_expressions(self):
m = ConcreteModel()
m.x = Var()
m.y = Var()
m.z = Var()
m.c = Constraint(expr=0 <= m.x + m.y - m.z * m.y / m.x + 7)
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m))
def test_binary_expressions(self):
m = ConcreteModel()
m.x = Var()
m.y = Var()
m.z = Var()
m.c = Constraint(expr=0 <= m.x + m.y - m.z * m.y / m.x + 7)
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m))
def test_disjunction_unsat(self):
m = ConcreteModel()
m.x1 = Var(bounds=(0, 8))
m.x2 = Var(bounds=(0, 8))
m.obj = Objective(expr=m.x1 + m.x2, sense=minimize)
m.y1 = Disjunct()
m.y2 = Disjunct()
m.y1.c1 = Constraint(expr=m.x1 >= 9)
m.y1.c2 = Constraint(expr=m.x2 >= 2)
m.y2.c1 = Constraint(expr=m.x1 >= 3)
m.y2.c2 = Constraint(expr=m.x2 >= 9)
m.djn = Disjunction(expr=[m.y1, m.y2])
self.assertFalse(satisfiable(m))
def test_disjunction_unsat(self):
m = ConcreteModel()
m.x1 = Var(bounds=(0, 8))
m.x2 = Var(bounds=(0, 8))
m.obj = Objective(expr=m.x1 + m.x2, sense=minimize)
m.y1 = Disjunct()
m.y2 = Disjunct()
m.y1.c1 = Constraint(expr=m.x1 >= 9)
m.y1.c2 = Constraint(expr=m.x2 >= 2)
m.y2.c1 = Constraint(expr=m.x1 >= 3)
m.y2.c2 = Constraint(expr=m.x2 >= 9)
m.djn = Disjunction(expr=[m.y1, m.y2])
self.assertFalse(satisfiable(m))
def test_unary_expressions(self):
m = ConcreteModel()
m.x = Var()
m.y = Var()
m.z = Var()
m.a = Var()
m.b = Var()
m.c = Var()
m.d = Var()
m.c1 = Constraint(expr=0 <= sin(m.x))
m.c2 = Constraint(expr=0 <= cos(m.y))
m.c3 = Constraint(expr=0 <= tan(m.z))
m.c4 = Constraint(expr=0 <= asin(m.a))
m.c5 = Constraint(expr=0 <= acos(m.b))
m.c6 = Constraint(expr=0 <= atan(m.c))
m.c7 = Constraint(expr=0 <= sqrt(m.d))
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m) is not False)
def test_unary_expressions(self):
m = ConcreteModel()
m.x = Var()
m.y = Var()
m.z = Var()
m.a = Var()
m.b = Var()
m.c = Var()
m.d = Var()
m.c1 = Constraint(expr=0 <= sin(m.x))
m.c2 = Constraint(expr=0 <= cos(m.y))
m.c3 = Constraint(expr=0 <= tan(m.z))
m.c4 = Constraint(expr=0 <= asin(m.a))
m.c5 = Constraint(expr=0 <= acos(m.b))
m.c6 = Constraint(expr=0 <= atan(m.c))
m.c7 = Constraint(expr=0 <= sqrt(m.d))
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m) is not False)
def test_multiple_disjunctions_sat(self):
m = ConcreteModel()
m.x1 = Var(bounds=(0, 8))
m.x2 = Var(bounds=(0, 8))
m.obj = Objective(expr=m.x1 + m.x2, sense=minimize)
m.y1 = Disjunct()
m.y2 = Disjunct()
m.y1.c1 = Constraint(expr=m.x1 >= 2)
m.y1.c2 = Constraint(expr=m.x2 >= 2)
m.y2.c1 = Constraint(expr=m.x1 >= 1)
m.y2.c2 = Constraint(expr=m.x2 >= 1)
m.djn1 = Disjunction(expr=[m.y1, m.y2])
m.z1 = Disjunct()
m.z2 = Disjunct()
m.z1.c1 = Constraint(expr=m.x1 <= 1)
m.z1.c2 = Constraint(expr=m.x2 <= 1)
m.z2.c1 = Constraint(expr=m.x1 <= 0)
m.z2.c2 = Constraint(expr=m.x2 <= 0)
m.djn2 = Disjunction(expr=[m.z1, m.z2])
self.assertTrue(satisfiable(m))
def test_multiple_disjunctions_sat(self):
m = ConcreteModel()
m.x1 = Var(bounds=(0, 8))
m.x2 = Var(bounds=(0, 8))
m.obj = Objective(expr=m.x1 + m.x2, sense=minimize)
m.y1 = Disjunct()
m.y2 = Disjunct()
m.y1.c1 = Constraint(expr=m.x1 >= 2)
m.y1.c2 = Constraint(expr=m.x2 >= 2)
m.y2.c1 = Constraint(expr=m.x1 >= 1)
m.y2.c2 = Constraint(expr=m.x2 >= 1)
m.djn1 = Disjunction(expr=[m.y1, m.y2])
m.z1 = Disjunct()
m.z2 = Disjunct()
m.z1.c1 = Constraint(expr=m.x1 <= 1)
m.z1.c2 = Constraint(expr=m.x2 <= 1)
m.z2.c1 = Constraint(expr=m.x1 <= 0)
m.z2.c2 = Constraint(expr=m.x2 <= 0)
m.djn2 = Disjunction(expr=[m.z1, m.z2])
self.assertTrue(satisfiable(m))
def test_binary_domains(self):
m = ConcreteModel()
m.x1 = Var(domain=Binary)
m.c1 = Constraint(expr=m.x1 == 2)
self.assertFalse(satisfiable(m))
def test_bounds_sat(self):
m = ConcreteModel()
m.x = Var(bounds=(0, 5))
m.c1 = Constraint(expr=4.99 == m.x)
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m))
def solve(self, model, **kwds):
config = self.CONFIG(kwds.pop('options', {}))
config.set_value(kwds)
return SolverFactory('gdpopt').solve(
model,
strategy='LBB',
minlp_solver=config.solver,
minlp_solver_args=config.solver_args,
tee=config.tee,
check_sat=config.check_sat,
logger=config.logger,
time_limit=config.time_limit)
# Validate model to be used with gdpbb
self.validate_model(model)
# Set solver as an MINLP
solve_data = GDPbbSolveData()
solve_data.timing = Container()
solve_data.original_model = model
solve_data.results = SolverResults()
old_logger_level = config.logger.getEffectiveLevel()
with time_code(solve_data.timing, 'total', is_main_timer=True), \
restore_logger_level(config.logger), \
create_utility_block(model, 'GDPbb_utils', solve_data):
if config.tee and old_logger_level > logging.INFO:
# If the logger does not already include INFO, include it.
config.logger.setLevel(logging.INFO)
config.logger.info(
"Starting GDPbb version %s using %s as subsolver" %
(".".join(map(str, self.version())), config.solver))
# Setup results
solve_data.results.solver.name = 'GDPbb - %s' % (str(
config.solver))
setup_results_object(solve_data, config)
# clone original model for root node of branch and bound
root = solve_data.working_model = solve_data.original_model.clone()
# get objective sense
process_objective(solve_data, config)
objectives = solve_data.original_model.component_data_objects(
Objective, active=True)
obj = next(objectives, None)
solve_data.results.problem.sense = obj.sense
# set up lists to keep track of which disjunctions have been covered.
# this list keeps track of the relaxed disjunctions
root.GDPbb_utils.unenforced_disjunctions = list(
disjunction
for disjunction in root.GDPbb_utils.disjunction_list
if disjunction.active)
root.GDPbb_utils.deactivated_constraints = ComponentSet([
constr
for disjunction in root.GDPbb_utils.unenforced_disjunctions
for disjunct in disjunction.disjuncts
for constr in disjunct.component_data_objects(ctype=Constraint,
active=True)
if constr.body.polynomial_degree() not in (1, 0)
])
# Deactivate nonlinear constraints in unenforced disjunctions
for constr in root.GDPbb_utils.deactivated_constraints:
constr.deactivate()
# Add the BigM suffix if it does not already exist. Used later during nonlinear constraint activation.
if not hasattr(root, 'BigM'):
root.BigM = Suffix()
# Pre-screen that none of the disjunctions are already predetermined due to the disjuncts being fixed
# to True/False values.
# TODO this should also be done within the loop, but we aren't handling it right now.
# Should affect efficiency, but not correctness.
root.GDPbb_utils.disjuncts_fixed_True = ComponentSet()
# Only find top-level (non-nested) disjunctions
for disjunction in root.component_data_objects(Disjunction,
active=True):
fixed_true_disjuncts = [
disjunct for disjunct in disjunction.disjuncts
if disjunct.indicator_var.fixed
and disjunct.indicator_var.value == 1
]
fixed_false_disjuncts = [
disjunct for disjunct in disjunction.disjuncts
if disjunct.indicator_var.fixed
and disjunct.indicator_var.value == 0
]
for disjunct in fixed_false_disjuncts:
disjunct.deactivate()
if len(fixed_false_disjuncts) == len(
disjunction.disjuncts) - 1:
# all but one disjunct in the disjunction is fixed to False. Remaining one must be true.
if not fixed_true_disjuncts:
fixed_true_disjuncts = [
disjunct for disjunct in disjunction.disjuncts
if disjunct not in fixed_false_disjuncts
]
# Reactivate the fixed-true disjuncts
for disjunct in fixed_true_disjuncts:
newly_activated = ComponentSet()
for constr in disjunct.component_data_objects(Constraint):
if constr in root.GDPbb_utils.deactivated_constraints:
newly_activated.add(constr)
constr.activate()
# Set the big M value for the constraint
root.BigM[constr] = 1
# Note: we use a default big M value of 1
# because all non-selected disjuncts should be deactivated.
# Therefore, none of the big M transformed nonlinear constraints will need to be relaxed.
# The default M value should therefore be irrelevant.
root.GDPbb_utils.deactivated_constraints -= newly_activated
root.GDPbb_utils.disjuncts_fixed_True.add(disjunct)
if fixed_true_disjuncts:
assert disjunction.xor, "GDPbb only handles disjunctions in which one term can be selected. " \
"%s violates this assumption." % (disjunction.name, )
root.GDPbb_utils.unenforced_disjunctions.remove(
disjunction)
# Check satisfiability
if config.check_sat and satisfiable(root, config.logger) is False:
# Problem is not satisfiable. Problem is infeasible.
obj_value = obj_sign * float('inf')
else:
# solve the root node
config.logger.info("Solving the root node.")
obj_value, result, var_values = self.subproblem_solve(
root, config)
if obj_sign * obj_value == float('inf'):
config.logger.info(
"Model was found to be infeasible at the root node. Elapsed %.2f seconds."
% get_main_elapsed_time(solve_data.timing))
if solve_data.results.problem.sense == minimize:
solve_data.results.problem.lower_bound = float('inf')
solve_data.results.problem.upper_bound = None
else:
solve_data.results.problem.lower_bound = None
solve_data.results.problem.upper_bound = float('-inf')
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.iterations = 0
solve_data.results.solver.termination_condition = tc.infeasible
return solve_data.results
# initialize minheap for Branch and Bound algorithm
# Heap structure: (ordering tuple, model)
# Ordering tuple: (objective value, disjunctions_left, -total_nodes_counter)
# - select solutions with lower objective value,
# then fewer disjunctions left to explore (depth first),
# then more recently encountered (tiebreaker)
heap = []
total_nodes_counter = 0
disjunctions_left = len(root.GDPbb_utils.unenforced_disjunctions)
heapq.heappush(heap,
((obj_sign * obj_value, disjunctions_left,
-total_nodes_counter), root, result, var_values))
# loop to branch through the tree
while len(heap) > 0:
# pop best model off of heap
sort_tuple, incumbent_model, incumbent_results, incumbent_var_values = heapq.heappop(
heap)
incumbent_obj_value, disjunctions_left, _ = sort_tuple
config.logger.info(
"Exploring node with LB %.10g and %s inactive disjunctions."
% (incumbent_obj_value, disjunctions_left))
# if all the originally active disjunctions are active, solve and
# return solution
if disjunctions_left == 0:
config.logger.info("Model solved.")
# Model is solved. Copy over solution values.
original_model = solve_data.original_model
for orig_var, val in zip(
original_model.GDPbb_utils.variable_list,
incumbent_var_values):
orig_var.value = val
solve_data.results.problem.lower_bound = incumbent_results.problem.lower_bound
solve_data.results.problem.upper_bound = incumbent_results.problem.upper_bound
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.iterations = total_nodes_counter
solve_data.results.solver.termination_condition = incumbent_results.solver.termination_condition
return solve_data.results
# Pick the next disjunction to branch on
next_disjunction = incumbent_model.GDPbb_utils.unenforced_disjunctions[
0]
config.logger.info("Branching on disjunction %s" %
next_disjunction.name)
assert next_disjunction.xor, "GDPbb only handles disjunctions in which one term can be selected. " \
"%s violates this assumption." % (next_disjunction.name, )
new_nodes_counter = 0
for i, disjunct in enumerate(next_disjunction.disjuncts):
# Create one branch for each of the disjuncts on the disjunction
if any(disj.indicator_var.fixed
and disj.indicator_var.value == 1
for disj in next_disjunction.disjuncts
if disj is not disjunct):
# If any other disjunct is fixed to 1 and an xor relationship applies,
# then this disjunct cannot be activated.
continue
# Check time limit
if get_main_elapsed_time(
solve_data.timing) >= config.time_limit:
if solve_data.results.problem.sense == minimize:
solve_data.results.problem.lower_bound = incumbent_obj_value
solve_data.results.problem.upper_bound = float(
'inf')
else:
solve_data.results.problem.lower_bound = float(
'-inf')
solve_data.results.problem.upper_bound = incumbent_obj_value
config.logger.info('GDPopt unable to converge bounds '
'before time limit of {} seconds. '
'Elapsed: {} seconds'.format(
config.time_limit,
get_main_elapsed_time(
solve_data.timing)))
config.logger.info(
'Final bound values: LB: {} UB: {}'.format(
solve_data.results.problem.lower_bound,
solve_data.results.problem.upper_bound))
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.iterations = total_nodes_counter
solve_data.results.solver.termination_condition = tc.maxTimeLimit
return solve_data.results
# Branch on the disjunct
child = incumbent_model.clone()
# TODO I am leaving the old branching system in place, but there should be
# something better, ideally that deals with nested disjunctions as well.
disjunction_to_branch = child.GDPbb_utils.unenforced_disjunctions.pop(
0)
child_disjunct = disjunction_to_branch.disjuncts[i]
child_disjunct.indicator_var.fix(1)
# Deactivate (and fix to 0) other disjuncts on the disjunction
for disj in disjunction_to_branch.disjuncts:
if disj is not child_disjunct:
disj.deactivate()
# Activate nonlinear constraints on the newly fixed child disjunct
newly_activated = ComponentSet()
for constr in child_disjunct.component_data_objects(
Constraint):
if constr in child.GDPbb_utils.deactivated_constraints:
newly_activated.add(constr)
constr.activate()
# Set the big M value for the constraint
child.BigM[constr] = 1
# Note: we use a default big M value of 1
# because all non-selected disjuncts should be deactivated.
# Therefore, none of the big M transformed nonlinear constraints will need to be relaxed.
# The default M value should therefore be irrelevant.
child.GDPbb_utils.deactivated_constraints -= newly_activated
child.GDPbb_utils.disjuncts_fixed_True.add(child_disjunct)
if disjunct in incumbent_model.GDPbb_utils.disjuncts_fixed_True:
# If the disjunct was already branched to True from a parent disjunct branching, just pass
# through the incumbent value without resolving. The solution should be the same as the parent.
total_nodes_counter += 1
ordering_tuple = (obj_sign * incumbent_obj_value,
disjunctions_left - 1,
-total_nodes_counter)
heapq.heappush(heap, (ordering_tuple, child, result,
incumbent_var_values))
new_nodes_counter += 1
continue
if config.check_sat and satisfiable(
child, config.logger) is False:
# Problem is not satisfiable. Skip this disjunct.
continue
obj_value, result, var_values = self.subproblem_solve(
child, config)
total_nodes_counter += 1
ordering_tuple = (obj_sign * obj_value,
disjunctions_left - 1,
-total_nodes_counter)
heapq.heappush(heap,
(ordering_tuple, child, result, var_values))
new_nodes_counter += 1
config.logger.info(
"Added %s new nodes with %s relaxed disjunctions to the heap. Size now %s."
% (new_nodes_counter, disjunctions_left - 1, len(heap)))
def test_simple_sat_model(self):
m = ConcreteModel()
m.x = Var()
m.c = Constraint(expr=1 == m.x)
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m))
def test_lower_bound_unsat(self):
m = ConcreteModel()
m.x = Var(bounds=(0, 5))
m.c = Constraint(expr=-0.01 == m.x)
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
def test_bounds_sat(self):
m = ConcreteModel()
m.x = Var(bounds=(0, 5))
m.c1 = Constraint(expr=4.99 == m.x)
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m))
def test_constrained_layout(self):
exfile = import_file(
join(exdir, 'constrained_layout', 'cons_layout_model.py'))
m = exfile.build_constrained_layout_model()
self.assertTrue(satisfiable(m) is not False)
def test_8PP(self):
exfile = import_file(
join(exdir, 'eight_process', 'eight_proc_model.py'))
m = exfile.build_eight_process_flowsheet()
self.assertTrue(satisfiable(m) is not False)
def solve(self, model, **kwds):
config = self.CONFIG(kwds.pop('options', {}))
config.set_value(kwds)
# Validate model to be used with gdpbb
self.validate_model(model)
# Set solver as an MINLP
solver = SolverFactory(config.solver)
solve_data = GDPbbSolveData()
solve_data.timing = Container()
solve_data.original_model = model
solve_data.results = SolverResults()
old_logger_level = config.logger.getEffectiveLevel()
with time_code(solve_data.timing, 'total'), \
restore_logger_level(config.logger), \
create_utility_block(model, 'GDPbb_utils', solve_data):
if config.tee and old_logger_level > logging.INFO:
# If the logger does not already include INFO, include it.
config.logger.setLevel(logging.INFO)
config.logger.info(
"Starting GDPbb version %s using %s as subsolver" %
(".".join(map(str, self.version())), config.solver))
# Setup results
solve_data.results.solver.name = 'GDPbb - %s' % (str(
config.solver))
setup_results_object(solve_data, config)
# Initialize list containing indicator vars for reupdating model after solving
indicator_list_name = unique_component_name(
model, "_indicator_list")
indicator_vars = []
for disjunction in model.component_data_objects(ctype=Disjunction,
active=True):
for disjunct in disjunction.disjuncts:
indicator_vars.append(disjunct.indicator_var)
setattr(model, indicator_list_name, indicator_vars)
# get objective sense
objectives = model.component_data_objects(Objective, active=True)
obj = next(objectives, None)
obj_sign = 1 if obj.sense == minimize else -1
solve_data.results.problem.sense = obj.sense
# clone original model for root node of branch and bound
root = model.clone()
# set up lists to keep track of which disjunctions have been covered.
# this list keeps track of the original disjunctions that were active and are soon to be inactive
root.GDPbb_utils.unenforced_disjunctions = list(
disjunction
for disjunction in root.GDPbb_utils.disjunction_list
if disjunction.active)
# this list keeps track of the disjunctions that have been activated by the branch and bound
root.GDPbb_utils.curr_active_disjunctions = []
# deactivate all disjunctions in the model
# self.indicate(root)
for djn in root.GDPbb_utils.unenforced_disjunctions:
djn.deactivate()
# Deactivate all disjuncts in model. To be reactivated when disjunction
# is reactivated.
for disj in root.component_data_objects(Disjunct, active=True):
disj._deactivate_without_fixing_indicator()
# Satisfiability check would go here
# solve the root node
config.logger.info("Solving the root node.")
obj_value, result, _ = self.subproblem_solve(root, solver, config)
# initialize minheap for Branch and Bound algorithm
# Heap structure: (ordering tuple, model)
# Ordering tuple: (objective value, disjunctions_left, -counter)
# - select solutions with lower objective value,
# then fewer disjunctions left to explore (depth first),
# then more recently encountered (tiebreaker)
heap = []
counter = 0
disjunctions_left = len(root.GDPbb_utils.unenforced_disjunctions)
heapq.heappush(
heap, ((obj_sign * obj_value, disjunctions_left, -counter),
root, result, root.GDPbb_utils.variable_list))
# loop to branch through the tree
while len(heap) > 0:
# pop best model off of heap
sort_tup, mdl, mdl_results, vars = heapq.heappop(heap)
old_obj_val, disjunctions_left, _ = sort_tup
config.logger.info(
"Exploring node with LB %.10g and %s inactive disjunctions."
% (old_obj_val, disjunctions_left))
# if all the originally active disjunctions are active, solve and
# return solution
if disjunctions_left == 0:
config.logger.info("Model solved.")
# Model is solved. Copy over solution values.
for orig_var, soln_var in zip(
model.GDPbb_utils.variable_list, vars):
orig_var.value = soln_var.value
solve_data.results.problem.lower_bound = mdl_results.problem.lower_bound
solve_data.results.problem.upper_bound = mdl_results.problem.upper_bound
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.termination_condition = mdl_results.solver.termination_condition
return solve_data.results
next_disjunction = mdl.GDPbb_utils.unenforced_disjunctions.pop(
0)
config.logger.info("Activating disjunction %s" %
next_disjunction.name)
next_disjunction.activate()
mdl.GDPbb_utils.curr_active_disjunctions.append(
next_disjunction)
djn_left = len(mdl.GDPbb_utils.unenforced_disjunctions)
for disj in next_disjunction.disjuncts:
disj._activate_without_unfixing_indicator()
if not disj.indicator_var.fixed:
disj.indicator_var = 0 # initially set all indicator vars to zero
added_disj_counter = 0
for disj in next_disjunction.disjuncts:
if not disj.indicator_var.fixed:
disj.indicator_var = 1
mnew = mdl.clone()
if not disj.indicator_var.fixed:
disj.indicator_var = 0
# Check feasibility
if config.check_sat and satisfiable(
mnew, config.logger) is False:
# problem is not satisfiable. Skip this disjunct.
continue
obj_value, result, vars = self.subproblem_solve(
mnew, solver, config)
counter += 1
ordering_tuple = (obj_sign * obj_value, djn_left, -counter)
heapq.heappush(heap, (ordering_tuple, mnew, result, vars))
added_disj_counter = added_disj_counter + 1
config.logger.info(
"Added %s new nodes with %s relaxed disjunctions to the heap. Size now %s."
% (added_disj_counter, djn_left, len(heap)))
def test_strip_pack(self):
exfile = import_file(
join(exdir, 'strip_packing', 'strip_packing_concrete.py'))
m = exfile.build_rect_strip_packing_model()
self.assertTrue(satisfiable(m))
def test_abs_expressions(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=-0.001 >= abs(m.x))
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
def test_unhandled_expressions(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=0 <= log(m.x))
self.assertTrue(satisfiable(m))
def test_strip_pack(self):
exfile = import_file(
join(exdir, 'strip_packing', 'strip_packing_concrete.py'))
m = exfile.build_rect_strip_packing_model()
self.assertTrue(satisfiable(m))
def test_simple_sat_model(self):
m = ConcreteModel()
m.x = Var()
m.c = Constraint(expr=1 == m.x)
m.o = Objective(expr=m.x)
self.assertTrue(satisfiable(m))
def test_real_domains(self):
m = ConcreteModel()
m.x1 = Var(domain=NonNegativeReals)
m.c1 = Constraint(expr=m.x1 == -1.3)
self.assertFalse(satisfiable(m))
def test_integer_domains(self):
m = ConcreteModel()
m.x1 = Var(domain=PositiveIntegers)
m.c1 = Constraint(expr=m.x1 == 0.5)
self.assertFalse(satisfiable(m))
def test_ex_633_trespalacios(self):
exfile = import_file(join(exdir, 'small_lit', 'ex_633_trespalacios.py'))
m = exfile.build_simple_nonconvex_gdp()
self.assertTrue(satisfiable(m) is not False)
def test_unhandled_expressions(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr= 0 <= log(m.x))
self.assertTrue(satisfiable(m))
def test_lower_bound_unsat(self):
m = ConcreteModel()
m.x = Var(bounds=(0, 5))
m.c = Constraint(expr=-0.01 == m.x)
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
def test_constrained_layout(self):
exfile = import_file(
join(exdir, 'constrained_layout', 'cons_layout_model.py'))
m = exfile.build_constrained_layout_model()
self.assertTrue(satisfiable(m) is not False)
def test_integer_domains(self):
m = ConcreteModel()
m.x1 = Var(domain = PositiveIntegers)
m.c1 = Constraint(expr = m.x1 == 0.5)
self.assertFalse(satisfiable(m))
def test_real_domains(self):
m = ConcreteModel()
m.x1 = Var(domain = NonNegativeReals)
m.c1 = Constraint(expr = m.x1 == -1.3)
self.assertFalse(satisfiable(m))
def test_abs_expressions(self):
m = ConcreteModel()
m.x = Var()
m.c1 = Constraint(expr=-0.001 >= abs(m.x))
m.o = Objective(expr=m.x)
self.assertFalse(satisfiable(m))
def test_binary_domains(self):
m = ConcreteModel()
m.x1 = Var(domain = Binary)
m.c1 = Constraint(expr = m.x1 == 2)
self.assertFalse(satisfiable(m))
def solve(self, model, **kwds):
config = self.CONFIG(kwds.pop('options', {}))
config.set_value(kwds)
# Validate model to be used with gdpbb
self.validate_model(model)
# Set solver as an MINLP
solve_data = GDPbbSolveData()
solve_data.timing = Container()
solve_data.original_model = model
solve_data.results = SolverResults()
old_logger_level = config.logger.getEffectiveLevel()
with time_code(solve_data.timing, 'total', is_main_timer=True), \
restore_logger_level(config.logger), \
create_utility_block(model, 'GDPbb_utils', solve_data):
if config.tee and old_logger_level > logging.INFO:
# If the logger does not already include INFO, include it.
config.logger.setLevel(logging.INFO)
config.logger.info(
"Starting GDPbb version %s using %s as subsolver"
% (".".join(map(str, self.version())), config.solver)
)
# Setup results
solve_data.results.solver.name = 'GDPbb - %s' % (str(config.solver))
setup_results_object(solve_data, config)
# clone original model for root node of branch and bound
root = solve_data.working_model = solve_data.original_model.clone()
# get objective sense
process_objective(solve_data, config)
objectives = solve_data.original_model.component_data_objects(Objective, active=True)
obj = next(objectives, None)
obj_sign = 1 if obj.sense == minimize else -1
solve_data.results.problem.sense = obj.sense
# set up lists to keep track of which disjunctions have been covered.
# this list keeps track of the relaxed disjunctions
root.GDPbb_utils.unenforced_disjunctions = list(
disjunction for disjunction in root.GDPbb_utils.disjunction_list if disjunction.active
)
root.GDPbb_utils.deactivated_constraints = ComponentSet([
constr for disjunction in root.GDPbb_utils.unenforced_disjunctions
for disjunct in disjunction.disjuncts
for constr in disjunct.component_data_objects(ctype=Constraint, active=True)
if constr.body.polynomial_degree() not in (1, 0)
])
# Deactivate nonlinear constraints in unenforced disjunctions
for constr in root.GDPbb_utils.deactivated_constraints:
constr.deactivate()
# Add the BigM suffix if it does not already exist. Used later during nonlinear constraint activation.
if not hasattr(root, 'BigM'):
root.BigM = Suffix()
# Pre-screen that none of the disjunctions are already predetermined due to the disjuncts being fixed
# to True/False values.
# TODO this should also be done within the loop, but we aren't handling it right now.
# Should affect efficiency, but not correctness.
root.GDPbb_utils.disjuncts_fixed_True = ComponentSet()
# Only find top-level (non-nested) disjunctions
for disjunction in root.component_data_objects(Disjunction, active=True):
fixed_true_disjuncts = [disjunct for disjunct in disjunction.disjuncts
if disjunct.indicator_var.fixed
and disjunct.indicator_var.value == 1]
fixed_false_disjuncts = [disjunct for disjunct in disjunction.disjuncts
if disjunct.indicator_var.fixed
and disjunct.indicator_var.value == 0]
for disjunct in fixed_false_disjuncts:
disjunct.deactivate()
if len(fixed_false_disjuncts) == len(disjunction.disjuncts) - 1:
# all but one disjunct in the disjunction is fixed to False. Remaining one must be true.
if not fixed_true_disjuncts:
fixed_true_disjuncts = [disjunct for disjunct in disjunction.disjuncts
if disjunct not in fixed_false_disjuncts]
# Reactivate the fixed-true disjuncts
for disjunct in fixed_true_disjuncts:
newly_activated = ComponentSet()
for constr in disjunct.component_data_objects(Constraint):
if constr in root.GDPbb_utils.deactivated_constraints:
newly_activated.add(constr)
constr.activate()
# Set the big M value for the constraint
root.BigM[constr] = 1
# Note: we use a default big M value of 1
# because all non-selected disjuncts should be deactivated.
# Therefore, none of the big M transformed nonlinear constraints will need to be relaxed.
# The default M value should therefore be irrelevant.
root.GDPbb_utils.deactivated_constraints -= newly_activated
root.GDPbb_utils.disjuncts_fixed_True.add(disjunct)
if fixed_true_disjuncts:
assert disjunction.xor, "GDPbb only handles disjunctions in which one term can be selected. " \
"%s violates this assumption." % (disjunction.name, )
root.GDPbb_utils.unenforced_disjunctions.remove(disjunction)
# Check satisfiability
if config.check_sat and satisfiable(root, config.logger) is False:
# Problem is not satisfiable. Problem is infeasible.
obj_value = obj_sign * float('inf')
else:
# solve the root node
config.logger.info("Solving the root node.")
obj_value, result, var_values = self.subproblem_solve(root, config)
if obj_sign * obj_value == float('inf'):
config.logger.info("Model was found to be infeasible at the root node. Elapsed %.2f seconds."
% get_main_elapsed_time(solve_data.timing))
if solve_data.results.problem.sense == minimize:
solve_data.results.problem.lower_bound = float('inf')
solve_data.results.problem.upper_bound = None
else:
solve_data.results.problem.lower_bound = None
solve_data.results.problem.upper_bound = float('-inf')
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.iterations = 0
solve_data.results.solver.termination_condition = tc.infeasible
return solve_data.results
# initialize minheap for Branch and Bound algorithm
# Heap structure: (ordering tuple, model)
# Ordering tuple: (objective value, disjunctions_left, -total_nodes_counter)
# - select solutions with lower objective value,
# then fewer disjunctions left to explore (depth first),
# then more recently encountered (tiebreaker)
heap = []
total_nodes_counter = 0
disjunctions_left = len(root.GDPbb_utils.unenforced_disjunctions)
heapq.heappush(
heap, (
(obj_sign * obj_value, disjunctions_left, -total_nodes_counter),
root, result, var_values))
# loop to branch through the tree
while len(heap) > 0:
# pop best model off of heap
sort_tuple, incumbent_model, incumbent_results, incumbent_var_values = heapq.heappop(heap)
incumbent_obj_value, disjunctions_left, _ = sort_tuple
config.logger.info("Exploring node with LB %.10g and %s inactive disjunctions." % (
incumbent_obj_value, disjunctions_left
))
# if all the originally active disjunctions are active, solve and
# return solution
if disjunctions_left == 0:
config.logger.info("Model solved.")
# Model is solved. Copy over solution values.
original_model = solve_data.original_model
for orig_var, val in zip(original_model.GDPbb_utils.variable_list, incumbent_var_values):
orig_var.value = val
solve_data.results.problem.lower_bound = incumbent_results.problem.lower_bound
solve_data.results.problem.upper_bound = incumbent_results.problem.upper_bound
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.iterations = total_nodes_counter
solve_data.results.solver.termination_condition = incumbent_results.solver.termination_condition
return solve_data.results
# Pick the next disjunction to branch on
next_disjunction = incumbent_model.GDPbb_utils.unenforced_disjunctions[0]
config.logger.info("Branching on disjunction %s" % next_disjunction.name)
assert next_disjunction.xor, "GDPbb only handles disjunctions in which one term can be selected. " \
"%s violates this assumption." % (next_disjunction.name, )
new_nodes_counter = 0
for i, disjunct in enumerate(next_disjunction.disjuncts):
# Create one branch for each of the disjuncts on the disjunction
if any(disj.indicator_var.fixed and disj.indicator_var.value == 1
for disj in next_disjunction.disjuncts if disj is not disjunct):
# If any other disjunct is fixed to 1 and an xor relationship applies,
# then this disjunct cannot be activated.
continue
# Check time limit
if get_main_elapsed_time(solve_data.timing) >= config.time_limit:
if solve_data.results.problem.sense == minimize:
solve_data.results.problem.lower_bound = incumbent_obj_value
solve_data.results.problem.upper_bound = float('inf')
else:
solve_data.results.problem.lower_bound = float('-inf')
solve_data.results.problem.upper_bound = incumbent_obj_value
config.logger.info(
'GDPopt unable to converge bounds '
'before time limit of {} seconds. '
'Elapsed: {} seconds'
.format(config.time_limit, get_main_elapsed_time(solve_data.timing)))
config.logger.info(
'Final bound values: LB: {} UB: {}'.
format(solve_data.results.problem.lower_bound, solve_data.results.problem.upper_bound))
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.iterations = total_nodes_counter
solve_data.results.solver.termination_condition = tc.maxTimeLimit
return solve_data.results
# Branch on the disjunct
child = incumbent_model.clone()
# TODO I am leaving the old branching system in place, but there should be
# something better, ideally that deals with nested disjunctions as well.
disjunction_to_branch = child.GDPbb_utils.unenforced_disjunctions.pop(0)
child_disjunct = disjunction_to_branch.disjuncts[i]
child_disjunct.indicator_var.fix(1)
# Deactivate (and fix to 0) other disjuncts on the disjunction
for disj in disjunction_to_branch.disjuncts:
if disj is not child_disjunct:
disj.deactivate()
# Activate nonlinear constraints on the newly fixed child disjunct
newly_activated = ComponentSet()
for constr in child_disjunct.component_data_objects(Constraint):
if constr in child.GDPbb_utils.deactivated_constraints:
newly_activated.add(constr)
constr.activate()
# Set the big M value for the constraint
child.BigM[constr] = 1
# Note: we use a default big M value of 1
# because all non-selected disjuncts should be deactivated.
# Therefore, none of the big M transformed nonlinear constraints will need to be relaxed.
# The default M value should therefore be irrelevant.
child.GDPbb_utils.deactivated_constraints -= newly_activated
child.GDPbb_utils.disjuncts_fixed_True.add(child_disjunct)
if disjunct in incumbent_model.GDPbb_utils.disjuncts_fixed_True:
# If the disjunct was already branched to True from a parent disjunct branching, just pass
# through the incumbent value without resolving. The solution should be the same as the parent.
total_nodes_counter += 1
ordering_tuple = (obj_sign * incumbent_obj_value, disjunctions_left - 1, -total_nodes_counter)
heapq.heappush(heap, (ordering_tuple, child, result, incumbent_var_values))
new_nodes_counter += 1
continue
if config.check_sat and satisfiable(child, config.logger) is False:
# Problem is not satisfiable. Skip this disjunct.
continue
obj_value, result, var_values = self.subproblem_solve(child, config)
total_nodes_counter += 1
ordering_tuple = (obj_sign * obj_value, disjunctions_left - 1, -total_nodes_counter)
heapq.heappush(heap, (ordering_tuple, child, result, var_values))
new_nodes_counter += 1
config.logger.info("Added %s new nodes with %s relaxed disjunctions to the heap. Size now %s." % (
new_nodes_counter, disjunctions_left - 1, len(heap)))
def test_8PP(self):
exfile = import_file(
join(exdir, 'eight_process', 'eight_proc_model.py'))
m = exfile.build_eight_process_flowsheet()
self.assertTrue(satisfiable(m) is not False)
def solve(self, model, **kwds):
config = self.CONFIG(kwds.pop('options', {}))
config.set_value(kwds)
# Validate model to be used with gdpbb
self.validate_model(model)
# Set solver as an MINLP
solver = SolverFactory(config.solver)
solve_data = GDPbbSolveData()
solve_data.timing = Container()
solve_data.original_model = model
solve_data.results = SolverResults()
old_logger_level = config.logger.getEffectiveLevel()
with time_code(solve_data.timing, 'total'), \
restore_logger_level(config.logger), \
create_utility_block(model, 'GDPbb_utils', solve_data):
if config.tee and old_logger_level > logging.INFO:
# If the logger does not already include INFO, include it.
config.logger.setLevel(logging.INFO)
config.logger.info(
"Starting GDPbb version %s using %s as subsolver"
% (".".join(map(str, self.version())), config.solver)
)
# Setup results
solve_data.results.solver.name = 'GDPbb - %s' % (str(config.solver))
setup_results_object(solve_data, config)
# Initialize list containing indicator vars for reupdating model after solving
indicator_list_name = unique_component_name(model, "_indicator_list")
indicator_vars = []
for disjunction in model.component_data_objects(
ctype=Disjunction, active=True):
for disjunct in disjunction.disjuncts:
indicator_vars.append(disjunct.indicator_var)
setattr(model, indicator_list_name, indicator_vars)
# get objective sense
objectives = model.component_data_objects(Objective, active=True)
obj = next(objectives, None)
obj_sign = 1 if obj.sense == minimize else -1
solve_data.results.problem.sense = obj.sense
# clone original model for root node of branch and bound
root = model.clone()
# set up lists to keep track of which disjunctions have been covered.
# this list keeps track of the original disjunctions that were active and are soon to be inactive
root.GDPbb_utils.unenforced_disjunctions = list(
disjunction for disjunction in root.GDPbb_utils.disjunction_list if disjunction.active
)
# this list keeps track of the disjunctions that have been activated by the branch and bound
root.GDPbb_utils.curr_active_disjunctions = []
# deactivate all disjunctions in the model
# self.indicate(root)
for djn in root.GDPbb_utils.unenforced_disjunctions:
djn.deactivate()
# Deactivate all disjuncts in model. To be reactivated when disjunction
# is reactivated.
for disj in root.component_data_objects(Disjunct, active=True):
disj._deactivate_without_fixing_indicator()
# Satisfiability check would go here
# solve the root node
config.logger.info("Solving the root node.")
obj_value, result, _ = self.subproblem_solve(root, solver, config)
# initialize minheap for Branch and Bound algorithm
# Heap structure: (ordering tuple, model)
# Ordering tuple: (objective value, disjunctions_left, -counter)
# - select solutions with lower objective value,
# then fewer disjunctions left to explore (depth first),
# then more recently encountered (tiebreaker)
heap = []
counter = 0
disjunctions_left = len(root.GDPbb_utils.unenforced_disjunctions)
heapq.heappush(heap,
((obj_sign * obj_value, disjunctions_left, -counter), root,
result, root.GDPbb_utils.variable_list))
# loop to branch through the tree
while len(heap) > 0:
# pop best model off of heap
sort_tup, mdl, mdl_results, vars = heapq.heappop(heap)
old_obj_val, disjunctions_left, _ = sort_tup
config.logger.info("Exploring node with LB %.10g and %s inactive disjunctions." % (
old_obj_val, disjunctions_left
))
# if all the originally active disjunctions are active, solve and
# return solution
if disjunctions_left == 0:
config.logger.info("Model solved.")
# Model is solved. Copy over solution values.
for orig_var, soln_var in zip(model.GDPbb_utils.variable_list, vars):
orig_var.value = soln_var.value
solve_data.results.problem.lower_bound = mdl_results.problem.lower_bound
solve_data.results.problem.upper_bound = mdl_results.problem.upper_bound
solve_data.results.solver.timing = solve_data.timing
solve_data.results.solver.termination_condition = mdl_results.solver.termination_condition
return solve_data.results
next_disjunction = mdl.GDPbb_utils.unenforced_disjunctions.pop(0)
config.logger.info("Activating disjunction %s" % next_disjunction.name)
next_disjunction.activate()
mdl.GDPbb_utils.curr_active_disjunctions.append(next_disjunction)
djn_left = len(mdl.GDPbb_utils.unenforced_disjunctions)
for disj in next_disjunction.disjuncts:
disj._activate_without_unfixing_indicator()
if not disj.indicator_var.fixed:
disj.indicator_var = 0 # initially set all indicator vars to zero
added_disj_counter = 0
for disj in next_disjunction.disjuncts:
if not disj.indicator_var.fixed:
disj.indicator_var = 1
mnew = mdl.clone()
if not disj.indicator_var.fixed:
disj.indicator_var = 0
# Check feasibility
if config.check_sat and satisfiable(mnew, config.logger) is False:
# problem is not satisfiable. Skip this disjunct.
continue
obj_value, result, vars = self.subproblem_solve(mnew, solver, config)
counter += 1
ordering_tuple = (obj_sign * obj_value, djn_left, -counter)
heapq.heappush(heap, (ordering_tuple, mnew, result, vars))
added_disj_counter = added_disj_counter + 1
config.logger.info("Added %s new nodes with %s relaxed disjunctions to the heap. Size now %s." % (
added_disj_counter, djn_left, len(heap)))
def test_ex_633_trespalacios(self):
exfile = import_file(join(exdir, 'small_lit', 'ex_633_trespalacios.py'))
m = exfile.build_simple_nonconvex_gdp()
self.assertTrue(satisfiable(m) is not False)