"""
Basic definitions and utilities.
Copyright by Gabriel A. Hackebeil (gabe.hackebeil@gmail.com).
"""
import enum
minimize = 1
"""The objective sense defining a minimization problem."""
maximize = -1
"""The objective sense defining a maximization problem."""
inf = float("inf")
"""A floating point constant set to ``float('inf')``."""
nan = float("nan")
"""A floating point constant set to ``float('nan')``."""
[docs]@enum.unique
class QueueStrategy(str, enum.Enum):
"""Strategies for prioritizing nodes in the central
dispatcher queue. For all strategies, ties are broken by
insertion order."""
bound = "bound"
"""The node with the worst bound is always selected
next."""
objective = "objective"
"""The node with the best objective is always selected
next."""
breadth = "breadth"
"""The node with the smallest tree depth is always
selected next (i.e., breadth-first search)."""
depth = "depth"
"""The node with the largest tree depth is always
selected next (i.e., depth-first search)."""
local_gap = "local_gap"
"""The node with the largest gap between its local
objective and bound is always selected next."""
fifo = "fifo"
"""Nodes are served in first-in, first-out order."""
lifo = "lifo"
"""Nodes are served in last-in, first-out order."""
random = "random"
"""Nodes are assigned a random priority before entering
the queue."""
custom = "custom"
"""The node with the largest value stored in the
:attr:`queue_priority <pybnb.node.Node.queue_priority>`
attribute is always selected next. Users are expected to
assign a priority to all nodes returned from the
:func:`branch <pybnb.problem.Problem.branch>`
method on their problem."""
_queue_strategy_to_int = {}
_int_to_queue_strategy = []
for _i, _val in enumerate(sorted(QueueStrategy,
key=lambda v: v.value)):
_queue_strategy_to_int[_val] = _i
_int_to_queue_strategy.append(_val)
del _i
del _val
[docs]@enum.unique
class SolutionStatus(str, enum.Enum):
"""Possible values assigned to the
:attr:`solution_status` attribute of a
:class:`SolverResults <pybnb.solver_results.SolverResults>`
object returned from a solve."""
optimal = "optimal"
"""Indicates that the best objective is finite and close
enough to the global bound to satisfy the optimality
tolerances used for the solve."""
feasible = "feasible"
"""Indicates that the best objective is finite but not
close enough to the global bound to satisfy the
optimality tolerances used for the solve."""
infeasible = "infeasible"
"""Indicates that both the best objective and global
bound are equal to the infeasible objective value (+inf
or -inf depending on the sense)."""
unbounded = "unbounded"
"""Indicates that both the best objective and global
bound are equal to the unbounded objective value (+inf
or -inf depending on the sense)."""
invalid = "invalid"
"""Indicates that the global bound is not a valid bound
on the best objective found. This may be due to an
ill-defined problem or other numerical issues."""
unknown = "unknown"
"""Indicates that the global bound is finite, but no
feasible (finite) objective was found."""
_solution_status_to_int = {}
_int_to_solution_status = []
for _i, _val in enumerate(sorted(SolutionStatus,
key=lambda v: v.value)):
_solution_status_to_int[_val] = _i
_int_to_solution_status.append(_val)
del _i
del _val
[docs]@enum.unique
class TerminationCondition(str, enum.Enum):
"""Possible values assigned to the
:attr:`termination_condition` attribute of a
:class:`SolverResults <pybnb.solver_results.SolverResults>`
object returned from a solve."""
optimality = "optimality"
"""The dispatcher terminated the solve based on
optimality criteria."""
objective_limit = "objective_limit"
"""The dispatcher terminated the solve based on the
user-supplied limit on the objective or bound being
satisfied."""
node_limit = "node_limit"
"""The dispatcher terminated the solve due to the
user-supplied explored node limit being surpassed."""
time_limit = "time_limit"
"""The dispatcher terminated the solve due to the
user-supplied time limit being surpassed."""
queue_empty = "queue_empty"
"""The dispatcher terminated the solve due to the node
queue becoming empty."""
queue_limit = "queue_limit"
"""The dispatcher terminated the solve due to the
user-supplied queue size limit being exceeded."""
interrupted = "interrupted"
"""Solve termination was initiated by SIGINT or SIGUSR
signal event."""
_termination_condition_to_int = {}
_int_to_termination_condition = []
for _i, _val in enumerate(sorted(TerminationCondition,
key=lambda v: v.value)):
_termination_condition_to_int[_val] = _i
_int_to_termination_condition.append(_val)
del _i
del _val