Instance

Instance#

class Instance#

Optimization problem instance.

Invariants#

Output-only variables are excluded from solver input and evaluated after the full state is populated.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x],
...     objective=3 * x,
...     constraints={},
...     sense=Sense.Maximize,
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> fixed = instance.partial_evaluate({0: 1})
>>> assert fixed.sense == Sense.Minimize
>>> assert fixed.objective.evaluate({}) == -3.0
>>> assert fixed.required_ids() == set()
>>> assert fixed.used_decision_variables == []
>>> assert fixed.populate_state({}).entries == {0: 1.0}
>>> solution = fixed.evaluate({})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 3.0)
__copy__() → Instance#
__deepcopy__(_memo: Any) → Instance#
__repr__() → str#
__str__() → str#
add_constraint(constraint: Constraint, name: Optional[str] = None, subscripts: Optional[Sequence[int]] = None, parameters: Optional[Mapping[str, str]] = None, description: Optional[str] = None) → AttachedConstraint#

Add a regular constraint to this instance.

Picks an unused ConstraintID, drains the wrapper’s context snapshot into this instance’s SoA store, and returns an AttachedConstraint bound to the new id. The input Constraint is not mutated; subsequent writes that should land in the instance must go through the returned handle. When modeling-label fields are provided, they replace the corresponding fields stored on the inserted constraint without modifying the input snapshot. Omitted fields preserve the snapshot’s existing values.

Args:

  • constraint: Constraint to add

  • name: Optional modeling name for the inserted constraint

  • subscripts: Optional integer indices for the inserted constraint

  • parameters: Optional string-valued indices for the inserted constraint

  • description: Optional description for the inserted constraint

Raises ValueError if the constraint references an undefined decision variable or one currently used as a substitution-dependency key, matching the validation performed by other constraint-insertion paths.

add_decision_variable(variable: DecisionVariable) → AttachedDecisionVariable#

Add a decision variable to this instance.

Drains the wrapper’s modeling-label snapshot into this instance’s SoA store and returns an AttachedDecisionVariable bound to the variable’s id — a write-through handle for further label updates. The original wrapper is not modified.

Raises ValueError if the variable’s id collides with an existing decision variable. Substituted variables retain their ids and therefore also count as existing decision variables.

add_indicator_constraint(constraint: IndicatorConstraint) → AttachedIndicatorConstraint#

Add an indicator constraint to this instance.

Picks an unused IndicatorConstraintID, drains the wrapper’s context snapshot into this instance’s SoA store, and returns an AttachedIndicatorConstraint bound to the new id.

Raises ValueError if the constraint references an undefined decision variable or one currently used as a substitution-dependency key.

add_integer_slack_to_inequality(constraint_id: int, slack_upper_bound: int) → Optional[float]#

Convert inequality \(f(x) \leq 0\) to inequality \(f(x) + b s \leq 0\) with an integer slack variable \(s\).

  • This should be used when convert_inequality_to_equality_with_integer_slack() is not applicable.

  • The bound of \(s\) will be \([0, \text{slack\_upper\_bound}]\), and the coefficient \(b\) is determined from the lower bound of \(f(x)\).

  • Since the slack variable is integer, the yielded inequality has residual error \(\min_s f(x) + b s\) at most \(b\). And thus \(b\) is returned to use scaling the penalty weight or other things.

    • Larger slack_upper_bound (i.e. finer-grained slack) yields smaller \(b\), and thus smaller the residual error, but it needs more bits for the slack variable, and thus the problem size becomes larger.

Returns: The coefficient \(b\) of the slack variable. If the constraint is trivially satisfied, this returns None.

Examples#

Let’s consider a simple inequality constraint x0 + 2*x1 <= 4.

>>> from ommx import DecisionVariable, Equality, Instance, Sense
>>> x = [
...     DecisionVariable.integer(i, lower=0, upper=3, name="x", subscripts=[i])
...     for i in range(3)
... ]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={0: x[0] + 2*x[1] <= 4},
...     sense=Sense.Maximize,
... )

Introduce an integer slack variable s in [0, 2]

>>> b = instance.add_integer_slack_to_inequality(
...     constraint_id=0,
...     slack_upper_bound=2
... )
>>> assert b == 2.0
>>> assert instance.constraints[0].function.terms == {
...     (0,): 1.0, (1,): 2.0, (3,): 2.0, (): -4.0
... }
>>> assert instance.constraints[0].equality == Equality.LessThanOrEqualToZero
add_one_hot_constraint(constraint: OneHotConstraint) → AttachedOneHotConstraint#

Add a one-hot constraint to this instance.

add_sos1_constraint(constraint: Sos1Constraint) → AttachedSos1Constraint#

Add a SOS1 constraint to this instance.

add_user_annotation(key: str, value: str, annotation_namespace: str = 'org.ommx.user.') → None#
add_user_annotations(annotations: Mapping[str, str], annotation_namespace: str = 'org.ommx.user.') → None#
as_hubo_format() → tuple[dict, float]#

Return the active objective in HUBO format without preparing the instance.

Postconditions#

The returned coefficients represent the active objective rather than preserved output semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x + 5, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> hubo, offset = instance.as_hubo_format()
>>> assert (hubo, offset) == ({(0,): -3.0}, -5.0)
>>> assert instance.objective.evaluate({0: 1}) == -8.0
>>> assert instance.evaluate({0: 1}).objective == 8.0
as_maximization_problem() → bool#

Convert the instance to a maximization problem.

If both the active objective and the output objective already use maximization, this does nothing.

Returns: True if either objective is converted, False if both already use maximization.

Postconditions#

Conversion changes both active and output objective semantics and is idempotent at the target sense. An existing output objective remains explicit even if both objectives become structurally equal.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Minimize
... )
>>> assert instance.convert_active_objective(Sense.Maximize)
>>> assert instance.evaluate({0: 1}).objective == 3.0
>>> assert instance.as_maximization_problem()
>>> solution = instance.evaluate({0: 1})
>>> assert instance.objective.evaluate({0: 1}) == -3.0
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, -3.0)
>>> assert not instance.as_maximization_problem()
as_minimization_problem() → bool#

Convert the instance to a minimization problem.

If both the active objective and the output objective already use minimization, this does nothing.

Returns: True if either objective is converted, False if both already use minimization.

Postconditions#

Conversion changes both active and output objective semantics and is idempotent at the target sense. An existing output objective remains explicit even if both objectives become structurally equal.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> assert instance.evaluate({0: 1}).objective == 3.0
>>> assert instance.as_minimization_problem()
>>> solution = instance.evaluate({0: 1})
>>> assert instance.objective.evaluate({0: 1}) == -3.0
>>> assert (solution.sense, solution.objective) == (Sense.Minimize, -3.0)
>>> assert not instance.as_minimization_problem()
as_parametric_instance() → ParametricInstance#

Convert this instance into a parameter-free parametric instance.

Postconditions#

Materializing the result without parameters preserves both active and output objective semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> restored = instance.as_parametric_instance().with_parameters({})
>>> assert restored.sense == Sense.Minimize
>>> assert restored.objective.evaluate({0: 1}) == -1.0
>>> solution = restored.evaluate({0: 1})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 1.0)
as_qubo_format() → tuple[dict, float]#

Return the active objective in QUBO format without preparing the instance.

Postconditions#

The returned coefficients represent the active objective rather than preserved output semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x + 5, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> qubo, offset = instance.as_qubo_format()
>>> assert (qubo, offset) == ({(0, 0): -3.0}, -5.0)
>>> assert instance.objective.evaluate({0: 1}) == -8.0
>>> assert instance.evaluate({0: 1}).objective == 8.0
attached_decision_variable(variable_id: int) → AttachedDecisionVariable#

Return an AttachedDecisionVariable bound to the given id — a write-through handle whose label setters update this instance’s SoA store. The handle also participates in arithmetic via ToFunction (only its id is consumed). Call detach() to obtain an independent DecisionVariable snapshot.

Raises KeyError if no variable with variable_id exists.

constraint_context_df(kind: Literal["regular", "indicator", "one_hot", "sos1"] = 'regular') → DataFrame#

Constraint context DataFrame (id-indexed wide format).

One row per constraint id (active + removed) with columns name, subscripts, description. Index column is {kind}_constraint_id. kind selects which constraint family to read: "regular", "indicator", "one_hot", or "sos1".

constraint_parameters_df(kind: Literal["regular", "indicator", "one_hot", "sos1"] = 'regular') → DataFrame#

Constraint parameters DataFrame (long format).

One row per (constraint_id, parameter_key) pair. Columns: {kind}_constraint_id, key, value. Default RangeIndex.

constraint_provenance_df(kind: Literal["regular", "indicator", "one_hot", "sos1"] = 'regular') → DataFrame#

Constraint provenance DataFrame (long format).

One row per (constraint_id, step) pair. Columns: {kind}_constraint_id, step, source_kind, source_id.

constraint_removed_reasons_df(kind: Literal["regular", "indicator", "one_hot", "sos1"] = 'regular') → DataFrame#

Removed-constraint reasons DataFrame (long format).

One row per (constraint_id, parameter_key) pair, plus one row with key/value set to NA when the reason has no parameters. Columns: {kind}_constraint_id, reason, key, value.

constraints_df(kind: Literal["regular", "indicator", "one_hot", "sos1"] = 'regular', include: Optional[Sequence[str]] = None, removed: bool = False) → DataFrame#

DataFrame of constraints, dispatched on kind=.

kind selects the constraint family — "regular", "indicator", "one_hot", or "sos1". The DataFrame is indexed by the kind- qualified id column ({kind}_constraint_id).

include selects which optional column families to fold in. It accepts a sequence of "label" / "parameters" / "removed_reason"; passing None (the default) yields the v2-equivalent shape (label + parameters). "removed_reason" is a unit flag that gates both the removed_reason column and the removed_reason.{key} parameter columns together.

removed=False (default) returns active constraints only. removed=True returns active + removed rows in the same DataFrame and auto-sets "removed_reason" so removed rows are distinguishable (active rows have NA in the reason columns).

convert_active_objective(target: Sense) → bool#

Convert only the active objective used by a solver-facing formulation.

This changes sense and objective to target while preserving the objective semantics returned by evaluate() and evaluate_samples(). Use as_minimization_problem() or as_maximization_problem() when the output objective should be converted as part of the mathematical problem itself.

Returns: True if the active objective is converted, False if it already has target.

Postconditions#

Conversion negates only the active objective and preserves evaluation semantics in either direction. Once captured, the output objective remains explicit even if a later conversion makes it structurally equal to the active objective.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> for source, target in ((Sense.Maximize, Sense.Minimize), (Sense.Minimize, Sense.Maximize)):
...     instance = Instance.from_components(
...         decision_variables=[x], objective=3 * x, constraints={}, sense=source
...     )
...     before = instance.evaluate({0: 1})
...     assert instance.convert_active_objective(target)
...     after = instance.evaluate({0: 1})
...     assert instance.sense == target
...     assert instance.objective.evaluate({0: 1}) == -3.0
...     assert (after.sense, after.objective) == (before.sense, before.objective)
...     assert not instance.convert_active_objective(target)
convert_all_indicators_to_constraints() → dict[int, list[int]]#

Convert every active indicator constraint to regular constraints using Big-M.

See convert_indicator_to_constraint() for the conversion rule. Returns a dict mapping each original indicator ID to the list of regular constraint IDs it produced.

Atomic: every active indicator is validated up front, and only if every one is convertible are the conversions applied. If any indicator fails validation (non-finite bound on a required side), no mutation happens and the instance is left untouched.

convert_all_one_hots_to_constraints() → list[int]#

Convert every active one-hot constraint to a regular equality constraint.

See convert_one_hot_to_constraint() for the conversion rule. Returns the IDs of the newly created regular constraints.

Examples#

>>> from ommx import Instance, DecisionVariable, OneHotConstraint
>>> x = [DecisionVariable.binary(i) for i in range(4)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={},
...     one_hot_constraints={
...         1: OneHotConstraint(variables=x[:2]),
...         2: OneHotConstraint(variables=x[2:]),
...     },
...     sense=Instance.MINIMIZE,
... )
>>> instance.convert_all_one_hots_to_constraints()
[0, 1]
>>> instance.one_hot_constraints
{}
>>> instance.constraints
{0: Constraint(x0 + x1 - 1 == 0), 1: Constraint(x2 + x3 - 1 == 0)}
convert_all_sos1_to_constraints() → dict[int, list[int]]#

Convert every active SOS1 constraint to regular constraints using Big-M.

See convert_sos1_to_constraints() for the conversion rule. Returns a dict mapping each original SOS1 ID to the list of regular constraint IDs it produced.

Atomic: every active SOS1 is validated up front, and only if every one is convertible are the conversions applied. If any SOS1 fails validation (unsupported kind, non-finite bound, domain excludes 0, etc.), no mutation happens and the instance is left untouched.

Examples#

>>> from ommx import Instance, DecisionVariable, Sos1Constraint
>>> x = [DecisionVariable.binary(i) for i in range(4)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={},
...     sos1_constraints={
...         1: Sos1Constraint(variables=x[:2]),
...         2: Sos1Constraint(variables=x[2:]),
...     },
...     sense=Instance.MINIMIZE,
... )
>>> instance.convert_all_sos1_to_constraints()
{1: [0], 2: [1]}
>>> instance.sos1_constraints
{}
>>> instance.constraints
{0: Constraint(x0 + x1 - 1 <= 0), 1: Constraint(x2 + x3 - 1 <= 0)}
convert_indicator_to_constraint(indicator_id: int) → list[int]#

Convert an indicator constraint to regular constraints using the Big-M method.

An indicator constraint y = 1 → f(x) <= 0 (or = 0) is encoded with upper and lower Big-M sides computed from the interval bounds of \(f(x)\):

\[ f(x) + u y - u \leq 0, \qquad -f(x) - l y + l \leq 0, \]

where \(u \geq \sup f(x)\) and \(l \leq \inf f(x)\) are the upper and lower bounds of \(f\) over the decision variables’ domains.

Side emission:

  • For <= indicators, only the upper side is considered; it is emitted iff \(u > 0\). If \(u \leq 0\) the constraint is already implied by the variable bounds and no Big-M is emitted.

  • For = indicators, both sides are considered independently: upper emitted iff \(u > 0\), lower emitted iff \(l < 0\).

When an equality side is skipped, the remaining constraints still enforce the implication correctly because the skipped inequality is already implied by the variable bounds: e.g. \(u \leq 0\) together with the emitted lower side forces \(f(x) = 0\) at \(y = 1\) when \(u = 0\), or renders \(y = 1\) infeasible when \(u < 0\) (correctly reflecting that \(f(x) = 0\) has no solution under the given bounds). When both \(u = 0\) and \(l = 0\), the bound says \(f(x) \equiv 0\) so the equality is vacuously satisfied and nothing is emitted.

Returns the list of newly created regular constraint IDs in insertion order (upper first, then lower). The list is empty when both sides are redundant.

Raises if the bound needed for an emitted side is non-finite, or if \(f(x)\) references a semi-continuous / semi-integer variable (the split domain \(\{0\} \cup [l, u]\) is not uniformly implemented, so Big-M conversion could silently drop the upper side when \(0 \notin [l, u]\)). The instance is not mutated on error.

Examples#

Convert an inequality indicator where the upper side is active:

>>> from ommx import (
...     Instance, DecisionVariable, IndicatorConstraint, Equality,
... )
>>> x = DecisionVariable.continuous(0, lower=0.0, upper=5.0)
>>> y = DecisionVariable.binary(1)
>>> ic = IndicatorConstraint(
...     indicator_variable=y,
...     function=x - 2,
...     equality=Equality.LessThanOrEqualToZero,
... )
>>> instance = Instance.from_components(
...     decision_variables=[x, y],
...     objective=x,
...     constraints={},
...     indicator_constraints={1: ic},
...     sense=Instance.MINIMIZE,
... )
>>> instance.convert_indicator_to_constraint(1)
[0]
>>> instance.indicator_constraints
{}
>>> instance.constraints
{0: Constraint(x0 + 3*x1 - 5 <= 0)}
convert_inequality_to_equality_with_integer_slack(constraint_id: int, max_integer_range: int) → None#

Convert an inequality constraint \(f(x) \leq 0\) to an equality constraint \(f(x) + s/a = 0\) with an integer slack variable \(s\).

  • Since \(a\) is determined as the minimal multiplier to make every coefficient of \(a f(x)\) integer, \(a\) itself and the range of \(s\) becomes impractically large. max_integer_range limits the maximal range of \(s\), and returns error if the range exceeds it.

  • Since this method evaluates the bound of \(f(x)\), we may find that:

    • The bound \([l, u]\) is strictly positive, i.e. \(l > 0\): this means the instance is infeasible because this constraint never be satisfied, and an error is raised.

    • The bound \([l, u]\) is always negative, i.e. \(u \leq 0\): this means this constraint is trivially satisfied, the constraint is moved to removed_constraints, and this method returns without introducing slack variable or raising an error.

Examples#

Let’s consider a simple inequality constraint x0 + 2*x1 <= 5.

>>> from ommx import DecisionVariable, Equality, Instance, Sense
>>> x = [
...     DecisionVariable.integer(i, lower=0, upper=3, name="x", subscripts=[i])
...     for i in range(3)
... ]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={0: x[0] + 2*x[1] <= 5},
...     sense=Sense.Maximize,
... )

Introduce an integer slack variable

>>> instance.convert_inequality_to_equality_with_integer_slack(
...     constraint_id=0,
...     max_integer_range=32
... )
>>> assert instance.constraints[0].function.terms == {
...     (0,): 1.0, (1,): 2.0, (3,): 1.0, (): -5.0
... }
>>> assert instance.constraints[0].equality == Equality.EqualToZero

Raises ExactIntegerSlackError when exact conversion is unavailable because the coefficients cannot be normalized or the slack range exceeds max_integer_range. Raises InfeasibleDetected when the bounds prove the inequality infeasible.

convert_one_hot_to_constraint(one_hot_id: int) → int#

Convert a one-hot constraint to a regular equality constraint.

A one-hot constraint over {x_1, ..., x_n} is mathematically equivalent to the linear equality x_1 + ... + x_n - 1 == 0. This method inserts that equality as a new regular constraint and moves the one-hot constraint into removed_one_hot_constraints with reason="ommx.Instance.convert_one_hot_to_constraint" and a constraint_id parameter pointing to the new regular constraint.

Returns the ID of the newly created regular constraint.

Examples#

>>> from ommx import Instance, DecisionVariable, OneHotConstraint
>>> x = [DecisionVariable.binary(i) for i in range(3)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={},
...     one_hot_constraints={1: OneHotConstraint(variables=x)},
...     sense=Instance.MINIMIZE,
... )
>>> new_id = instance.convert_one_hot_to_constraint(1)
>>> instance.one_hot_constraints
{}
>>> instance.constraints
{0: Constraint(x0 + x1 + x2 - 1 == 0)}
>>> instance.removed_one_hot_constraints
{1: RemovedOneHotConstraint(OneHotConstraint(exactly one of {x0, x1, x2} = 1), reason=ommx.Instance.convert_one_hot_to_constraint, constraint_id=0)}
convert_sos1_to_constraints(sos1_id: int) → list[int]#

Convert a SOS1 constraint to regular constraints using the Big-M method.

A SOS1 constraint over \(\{x_1, \ldots, x_n\}\) with each \(x_i \in [l_i, u_i]\) asserts that at most one \(x_i\) is non-zero. Per variable, a binary indicator \(y_i\) is introduced with the Big-M pair

\[ x_i - u_i y_i \leq 0, \qquad l_i y_i - x_i \leq 0 \]

(trivial sides \(u_i = 0\) or \(l_i = 0\) are skipped), together with the single cardinality constraint

\[ \sum_i y_i - 1 \leq 0. \]

If \(x_i\) is already binary with bound \([0, 1]\), \(x_i\) itself is reused as its indicator (no new variable, no Big-M pair).

Returns the list of newly created regular constraint IDs in insertion order (Big-M upper/lower pairs per non-binary variable, followed by the cardinality sum).

Raises if any \(x_i\) has a non-binary bound that is not finite, if its domain excludes \(0\), or if its kind is semi-continuous / semi-integer (the split domain \(\{0\} \cup [l, u]\) is not uniformly implemented across the codebase yet, so Big-M conversion of these kinds is not supported). The instance is not mutated on error.

Examples#

All-binary SOS1 reduces to sum(x_i) - 1 <= 0 without extra variables:

>>> from ommx import Instance, DecisionVariable, Sos1Constraint
>>> x = [DecisionVariable.binary(i) for i in range(3)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={},
...     sos1_constraints={1: Sos1Constraint(variables=x)},
...     sense=Instance.MINIMIZE,
... )
>>> instance.convert_sos1_to_constraints(1)
[0]
>>> instance.sos1_constraints
{}
>>> instance.constraints
{0: Constraint(x0 + x1 + x2 - 1 <= 0)}
>>> instance.removed_sos1_constraints
{1: RemovedSos1Constraint(Sos1Constraint(at most one of {x0, x1, x2} ≠ 0), reason=ommx.Instance.convert_sos1_to_constraints, constraint_ids=0)}
decision_variable_role(id: int) → Optional[DecisionVariableRole]#

Return the state role of a decision variable.

The role is one of used, fixed, dependent, or irrelevant. Unknown IDs return None.

decision_variable_roles() → dict[int, DecisionVariableRole]#

Return the state role of every decision variable, keyed by ID.

decision_variables_df(include: Optional[Sequence[str]] = None) → DataFrame#

DataFrame of decision variables

dependent_decision_variable_ids() → set[int]#

Return IDs of decision variables defined by decision_variable_dependency.

display_function(function: ToFunction, max_terms: Optional[int] = 100, max_chars: Optional[int] = 20000) → FunctionDisplay#

Build a bounded notebook display object for a function in this instance’s context.

By default this returns a preview capped at 100 complete terms and 20,000 characters. Use format_function() for an unbounded plain text string.

empty() → Instance#

Deprecated

Use Instance.minimize() instead.

Create trivial empty instance of minimization with zero objective, no constraints, and no decision variables.

Examples#

>>> from ommx import Instance
>>> instance = Instance.minimize()
>>> instance.sense == Instance.MINIMIZE
True
evaluate(state: ToState, atol: Optional[float] = None) → Solution#

Evaluate the given State into a Solution.

Postconditions#

Evaluation populates the full state before applying preserved output objective semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> fixed = instance.partial_evaluate({0: 1})
>>> solution = fixed.evaluate({})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 3.0)

Errors#

Evaluation raises ValueError when an active required ID is missing.

>>> required = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Minimize
... )
>>> try:
...     required.evaluate({})
... except ValueError as error:
...     assert "missing required variable IDs" in str(error)
... else:
...     raise AssertionError("evaluation accepted a missing active ID")
evaluate_samples(samples: ToSamples, atol: Optional[float] = None) → SampleSet#

Evaluate samples into a sample set.

Postconditions#

Every sample restores fixed variables before applying preserved output objective semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> fixed = instance.partial_evaluate({0: 1})
>>> sample_set = fixed.evaluate_samples({7: {}})
>>> assert sample_set.sense == Sense.Maximize
>>> assert sample_set.objectives[7] == 3.0
>>> assert sample_set.get(7).state.entries == {0: 1.0}
fixed_decision_variables() → dict[int, float]#

Return fixed decision variables as {id: fixed_value}.

format_function(function: ToFunction, max_terms: Optional[int] = None, max_chars: Optional[int] = None) → str#

Format a function using this instance’s decision-variable labels.

The plain repr() / str() representation of Function remains context-free and renders raw x<id> symbols such as x1. Use this method when labels from this instance should be used instead.

from_components(sense: Sense, objective: ToFunction, decision_variables: Sequence[DecisionVariable], constraints: Mapping[int, Constraint], indicator_constraints: Optional[Mapping[int, IndicatorConstraint]] = None, one_hot_constraints: Optional[Mapping[int, OneHotConstraint]] = None, sos1_constraints: Optional[Mapping[int, Sos1Constraint]] = None, named_functions: Optional[Sequence[NamedFunction]] = None, description: Optional[InstanceDescription] = None) → Instance#

Create an instance from its components.

Args:

  • sense: Optimization sense (minimize or maximize)

  • objective: Objective function

  • decision_variables: List of decision variables

  • constraints: List of constraints

  • named_functions: Optional list of named functions

  • description: Optional instance description

Returns: A new Instance

from_v1_bytes(bytes: bytes) → Instance#
from_v2_bytes(bytes: bytes) → Instance#
get_constraint_by_id(constraint_id: int) → Constraint#

Get a specific constraint by ID

get_decision_variable_by_id(variable_id: int) → DecisionVariable#

Get a specific decision variable by ID

get_named_function_by_id(named_function_id: int) → NamedFunction#

Get a specific named function by ID

get_removed_constraint_by_id(constraint_id: int) → RemovedConstraint#

Get a specific removed constraint by ID

get_user_annotation(key: str, annotation_namespace: str = 'org.ommx.user.') → str#
get_user_annotations(annotation_namespace: str = 'org.ommx.user.') → dict[str, str]#
irrelevant_decision_variable_ids() → set[int]#

Return IDs of decision variables not used, fixed, or dependent.

load_mps(path: str) → Instance#
load_qplib(path: str) → Instance#
log_encode(decision_variable_ids: set[int] = set(), atol: Optional[float] = None) → None#

Log-encode the integer decision variables.

Log encoding of an integer variable \(x \in [l, u]\) is to represent by \(m\) bits \(b_i \in \{0, 1\}\) by:

\[x = \sum_{i=0}^{m-2} 2^i b_i + (u - l - 2^{m-1} + 1) b_{m-1} + l\]

where \(m = \lceil \log_2(u - l + 1) \rceil\).

Args:

  • decision_variable_ids: The IDs of the integer decision variables to log-encode. If not specified (or empty), all used integer variables are log-encoded.

  • atol: Optional absolute tolerance used when normalizing integer bounds before encoding. If None, uses the default tolerance.

Raises LogEncodingError when an exact representation is unavailable for a requested variable. Allocation and expression-rewrite failures retain their original exception types.

Postconditions#

Encoding preserves existing output semantics, or captures the pre-encoding active objective when no output objective exists, while rewriting the active objective.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.integer(0, lower=0, upper=3)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> instance.log_encode({0})
>>> encoded_ids = instance.required_ids()
>>> assert len(encoded_ids) == 2
>>> state = {variable_id: 1 for variable_id in encoded_ids}
>>> assert instance.objective.evaluate(state) == 3.0
>>> solution = instance.evaluate(state)
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 3.0)
logical_memory_profile() → str#

Generate folded stack format for memory profiling of this instance.

This method generates a format compatible with flamegraph visualization tools like flamegraph.pl and inferno. Each line has the format: “frame1;frame2;…;frameN bytes”

The output shows the hierarchical memory structure of the instance, making it easy to identify which components are consuming the most memory.

To visualize with flamegraph:

  1. Save the output to a file: profile.txt

  2. Generate SVG: flamegraph.pl profile.txt > memory.svg

  3. Open memory.svg in a browser

Returns: Folded stack format string that can be visualized with flamegraph tools

Examples#

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = [DecisionVariable.binary(i) for i in range(3)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=x[0] + x[1],
...     constraints={},
...     sense=Sense.Maximize,
... )
>>> profile = instance.logical_memory_profile()
>>> isinstance(profile, str)
True
lower_special_constraints(kinds_to_lower: set[SpecialConstraintKind]) → set[SpecialConstraintKind]#

Lower selected active special constraint kinds into regular constraints.

For every kind in kinds_to_lower, the corresponding bulk conversion is invoked (:meth:convert_all_indicators_to_constraints, :meth:convert_all_one_hots_to_constraints, or :meth:convert_all_sos1_to_constraints) when that kind is active. The instance is mutated in place. Kinds omitted from kinds_to_lower remain active, and an empty set is a no-op. This does not establish :class:InstanceClass membership; check the resulting input separately.

Returns the set of :class:SpecialConstraintKind values that were requested and active, and therefore actually lowered. Empty when no requested kind was active.

Kinds are processed in Indicator, OneHot, Sos1 order. Each individual family conversion is atomic, but the whole operation is not: an error in a later family does not roll back families already lowered.

Raises if any underlying Big-M conversion fails (e.g. a SOS1 variable with a non-finite bound).

map_active_optimality(active: Optimality) → Optimality#

Map an optimality status for the active solver-facing formulation to the objective semantics returned by evaluation.

When the instance records that active-formulation optimality does not transport to its output objective, this returns Unspecified.

Postconditions#

Optimality is preserved for equivalent objective conversion and discarded after penalty preparation.

>>> from ommx import DecisionVariable, Instance, Optimality, Sense
>>> x = DecisionVariable.binary(0)
>>> equivalent = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert equivalent.convert_active_objective(Sense.Minimize)
>>> statuses = (Optimality.Unspecified, Optimality.Optimal, Optimality.NotOptimal)
>>> for status in statuses:
...     assert equivalent.map_active_optimality(status) == status
>>> penalized = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Minimize
... )
>>> _ = penalized.to_qubo(uniform_penalty_weight=1.0)
>>> for status in statuses:
...     assert penalized.map_active_optimality(status) == Optimality.Unspecified
maximize() → Instance#

Create an empty maximization instance with a zero objective.

Decision variables and constraints can be added incrementally with new_binary() and add_constraint().

minimize() → Instance#

Create an empty minimization instance with a zero objective.

Decision variables and constraints can be added incrementally with new_binary() and add_constraint().

named_functions_df(include: Optional[Sequence[str]] = None) → DataFrame#

DataFrame of named functions

new_binary(name: Optional[str] = None, subscripts: Sequence[int] = [], parameters: Mapping[str, str] = {}, description: Optional[str] = None) → AttachedDecisionVariable#

Create and add a binary decision variable with an automatically assigned ID.

Returns an AttachedDecisionVariable that can be used directly in expressions. The numeric ID remains available through its id property.

Args:

  • name: Optional human-readable modeling name. Names need not be unique.

  • subscripts: Optional integer indices from the source model.

  • parameters: Optional string-valued indices from the source model.

  • description: Optional human-readable description.

Raises ValueError if the maximum decision-variable ID is 2**64 - 1 and no larger automatic ID can be assigned.

partial_evaluate(state: ToState, atol: Optional[float] = None) → Instance#

Creates a new instance with specific decision variables fixed to given values.

This method substitutes the specified decision variables with their provided values, creating a new problem instance where these variables are fixed. This is useful for scenarios such as:

  • Creating simplified sub-problems with some variables fixed

  • Incrementally solving a problem by fixing some variables and optimizing the rest

  • Testing specific configurations of a problem

Args:

  • state: Maps decision variable IDs to their fixed values. Can be a State object or a dictionary mapping variable IDs to values.

  • atol: Absolute tolerance for floating point comparisons. If None, uses the default tolerance.

Returns: A new instance with the specified decision variables fixed to their given values.

Postconditions#

The new instance rewrites only active expressions while retaining fixed values for output evaluation.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> fixed = instance.partial_evaluate({0: 1})
>>> assert instance.required_ids() == {0}
>>> assert fixed.required_ids() == set()
>>> assert fixed.objective.evaluate({}) == -3.0
>>> assert fixed.attached_decision_variable(0).substituted_value == 1.0
>>> solution = fixed.evaluate({})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 3.0)
penalty_method() → ParametricInstance#

Convert to a parametric unconstrained instance by penalty method.

Roughly, this converts a constrained problem:

\[\min_x f(x) \quad \text{s.t.} \quad g_i(x) = 0 \; (\forall i), \quad h_j(x) \leq 0 \; (\forall j)\]

to an unconstrained problem with parameters:

\[\min_x f(x) + \sum_i \lambda_i g_i(x)^2 + \sum_j \rho_j h_j(x)^2\]

where \(\lambda_i\) and \(\rho_j\) are the penalty weight parameters for each constraint. If you want to use single weight parameter, use uniform_penalty_method() instead.

The removed constraints are stored in removed_constraints.

Note: This method converts inequality constraints \(h(x) \leq 0\) to \(|h(x)|^2\) not to \(\max(0, h(x))^2\). This means the penalty is enforced even for \(h(x) < 0\) cases, and \(h(x) = 0\) is unfairly favored. This feature is intended to use with add_integer_slack_to_inequality().

Postconditions#

Penalty conversion preserves existing output semantics, or captures the pre-penalty active objective when no output objective exists; materialization evaluates the penalty energy actively and invalidates optimality transport.

>>> from ommx import DecisionVariable, Instance, Optimality, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Minimize
... )
>>> parametric = instance.penalty_method()
>>> parameters = {parameter.id: 2.0 for parameter in parametric.parameters}
>>> prepared = parametric.with_parameters(parameters)
>>> assert parametric.constraints == {}
>>> assert 7 in parametric.removed_constraints
>>> assert prepared.objective.evaluate({0: 0}) == 2.0
>>> solution = prepared.evaluate({0: 0})
>>> assert (solution.sense, solution.objective, solution.feasible) == (Sense.Minimize, 0.0, False)
>>> assert prepared.map_active_optimality(Optimality.Optimal) == Optimality.Unspecified
populate_state(state: ToState, atol: Optional[float] = None) → State#

Populate fixed, irrelevant, and dependent decision variables in a state.

The input state must contain all decision variables that are actually used by this instance’s objective and active constraints. The returned State contains every decision variable in the instance.

Postconditions#

The returned state restores fixed variables needed only by preserved output semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> fixed = instance.partial_evaluate({0: 1})
>>> assert fixed.populate_state({}).entries == {0: 1.0}
>>> assert fixed.evaluate({}).objective == 3.0
prepare(input_class: InstanceClass, policy: PreparationPolicy) → None#

Apply the caller’s policy to this instance in place to reach input_class membership.

Selected phases are applied at most once in this order, stopping as soon as membership is reached:

  1. special_constraints: lower_special_constraints()

  2. objective: convert_active_objective()

  3. integer_slack: convert_inequality_to_equality_with_integer_slack(), followed by add_integer_slack_to_inequality() only when exact conversion is unavailable and slack_upper_bound is set

  4. fixed_penalty

  5. integer_encoding: log_encode()

  6. binary_power_reduction: reduce_binary_power()

Success guarantees input_class membership. When input_class is an Adapter’s INPUT_CLASS, that membership is the complete applicability condition; converter-local or backend failures may still occur later. This operation is not transactional, so an error may leave the instance changed. PreparationTargetNotReachedError exposes the final membership report when the selections do not reach input_class.

Postconditions#

Selected owner operations establish their own output semantics, and successful composition reaches the target class.

>>> from ommx import DecisionVariable, Instance, InstanceClass, Optimality, PreparationPolicy, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Maximize
... )
>>> policy = PreparationPolicy.for_qubo(uniform_penalty_weight=2.0)
>>> assert instance.prepare(InstanceClass.qubo(), policy) is None
>>> assert InstanceClass.qubo().contains(instance)
>>> assert instance.sense == Sense.Minimize
>>> assert instance.objective.evaluate({0: 0}) == 2.0
>>> solution = instance.evaluate({0: 0})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 0.0)
>>> assert instance.map_active_optimality(Optimality.Optimal) == Optimality.Unspecified
random_samples(rng: Rng, num_different_samples: int = 5, num_samples: int = 10, max_sample_id: Optional[int] = None) → Samples#

Generate random samples for this instance.

The generated samples will contain num_samples sample entries divided into num_different_samples groups, where each group shares the same state but has different sample IDs.

Args:

  • rng: Random number generator

  • num_different_samples: Number of different states to generate

  • num_samples: Total number of samples to generate

  • max_sample_id: Maximum sample ID (default: num_samples)

Returns: Samples object

Raises ValueError if the requested state groups cannot partition the samples or the inclusive sample-ID range is too small. num_different_samples=0 is valid only when num_samples=0.

Examples#

Generate samples for a simple instance:

>>> from ommx import DecisionVariable, Instance, Rng, Sense
>>> x = [DecisionVariable.binary(i) for i in range(3)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={0: sum(x) <= 2},
...     sense=Sense.Maximize,
... )

>>> rng = Rng()
>>> samples = instance.random_samples(rng, num_different_samples=2, num_samples=5)
>>> samples.num_samples()
5
random_state(rng: Rng) → State#

Generate a random state for this instance using the provided random number generator.

This method generates random values only for variables that are actually used in the objective function or constraints, as determined by decision variable usage. Generated values respect the bounds of each variable type.

Args:

  • rng: Random number generator to use for generating the state.

Returns: A randomly generated state that satisfies the variable bounds of this instance. Only contains values for variables that are used in the problem.

Examples#

Generate random state only for used variables

>>> from ommx import DecisionVariable, Instance, Rng, Sense
>>> x = [DecisionVariable.binary(i) for i in range(5)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=x[0] + x[1],
...     constraints={},
...     sense=Sense.Maximize,
... )

>>> rng = Rng()
>>> state = instance.random_state(rng)

Only used variables have values

>>> set(state.entries.keys())
{0, 1}

Values respect binary bounds

>>> all(state.entries[i] in [0.0, 1.0] for i in state.entries)
True
reduce_binary_power() → bool#

Reduce binary powers in the instance.

This method replaces binary powers in the instance with their equivalent linear expressions. For binary variables, \(x^n = x\) for any \(n \geq 1\), so we can reduce higher powers to linear terms.

Returns: True if any reduction was performed, False otherwise.

Postconditions#

Reduction preserves existing output semantics, or captures the pre-reduction active objective when no output objective exists, while rewriting active expressions.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x * x * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.reduce_binary_power()
>>> assert instance.objective.evaluate({0: 1}) == 1.0
>>> solution = instance.evaluate({0: 1})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 1.0)
>>> assert not instance.reduce_binary_power()
relax_constraint(constraint_id: int, reason: str, parameters: str) → None#

Remove a constraint from the instance.

The removed constraint is stored in removed_constraints, and can be restored by restore_constraint().

Args:

  • constraint_id: The ID of the constraint to remove.

  • reason: The reason why the constraint is removed.

  • parameters: Additional parameters to describe the reason.

Examples#

Relax constraint, and restore it.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = [DecisionVariable.binary(i) for i in range(3)]
>>> instance = Instance.from_components(
...     decision_variables=x,
...     objective=sum(x),
...     constraints={1: sum(x) == 3},
...     sense=Sense.Maximize,
... )
>>> assert set(instance.constraints) == {1}

>>> instance.relax_constraint(1, "manual relaxation")
>>> assert not instance.constraints
>>> assert set(instance.removed_constraints) == {1}

>>> instance.restore_constraint(1)
>>> assert set(instance.constraints) == {1}
>>> assert not instance.removed_constraints
relax_indicator_constraint(constraint_id: int, reason: str, parameters: str) → None#

Relax an indicator constraint by moving it from active to removed.

replace_annotations(annotations: Mapping[str, str]) → None#
required_ids() → set[int]#

Get the decision variable IDs required by the active formulation.

Postconditions#

IDs referenced only by preserved output semantics are not required solver inputs.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> fixed = instance.partial_evaluate({0: 1})
>>> assert fixed.required_ids() == set()
>>> assert fixed.evaluate({}).objective == 1.0
restore_constraint(constraint_id: int) → None#
restore_indicator_constraint(constraint_id: int) → None#

Restore a removed indicator constraint back to active.

save_mps(path: str, compress: bool = True) → None#
stats() → dict#

Get statistics about the instance.

Returns a dictionary containing counts of decision variables and constraints categorized by kind, usage, and status.

Returns: A dictionary with the following structure:

{
    "decision_variables": {
        "total": int,
        "by_kind": {
            "binary": int,
            "integer": int,
            "continuous": int,
            "semi_integer": int,
            "semi_continuous": int
        },
        "by_usage": {
            "used_in_objective": int,
            "used_in_constraints": int,
            "used": int,
            "fixed": int,
            "dependent": int,
            "irrelevant": int
        }
    },
    "constraints": {
        "total": int,
        "active": int,
        "removed": int
    }
}

Examples#

>>> from ommx import Instance
>>> instance = Instance.minimize()
>>> stats = instance.stats()
>>> stats["decision_variables"]["total"]
0
>>> stats["constraints"]["total"]
0
substitute(assignments: Mapping[int, ToFunction]) → None#

Substitute decision variables with function expressions (in-place).

Replaces each given decision variable with the provided function in the objective and all active constraints. This is the general substitution mechanism behind log_encode(), exposed so that users can implement their own integer encodings (e.g. unary, one-hot).

Args:

  • assignments: A dict mapping decision variable IDs to the function expressions that should replace them.

Important: This method performs an algebraic rewrite. It does not automatically translate the substituted variable’s bound or kind into constraints on the replacement expression. For example, substituting a binary variable x with y + z does not add 0 <= y + z <= 1, and substituting an integer variable does not ensure that the replacement expression is integral. If the substitution must preserve the optimization problem, the caller must provide a domain-preserving encoding or add the required linking and bound constraints explicitly.

Raises ValueError on cyclic or recursive assignments, or when substituting a variable that is a member of an indicator, one-hot, or SOS1 constraint.

Postconditions#

Substitution rewrites the active objective while output evaluation restores the substituted variable value.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> b = DecisionVariable.binary(1)
>>> instance = Instance.from_components(
...     decision_variables=[x, b], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> instance.substitute({0: b})
>>> assert instance.required_ids() == {1}
>>> assert instance.objective.evaluate({1: 1}) == -1.0
>>> solution = instance.evaluate({1: 1})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 1.0)
to_hubo(uniform_penalty_weight: Optional[float] = None, penalty_weights: Optional[Mapping[int, float]] = None, inequality_integer_slack_max_range: int = 31) → tuple[dict, float]#

Convert the instance to a HUBO format.

Postconditions#

The driver is equivalent to HUBO Preparation followed by active-objective formatting and preserves the output semantics present on entry.

>>> import copy
>>> from ommx import DecisionVariable, Instance, InstanceClass, PreparationPolicy, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Maximize
... )
>>> explicit = copy.copy(instance)
>>> policy = PreparationPolicy.for_hubo(uniform_penalty_weight=2.0)
>>> _ = explicit.prepare(InstanceClass.hubo(), policy)
>>> expected = explicit.as_hubo_format()
>>> actual = instance.to_hubo(uniform_penalty_weight=2.0)
>>> assert actual == expected
>>> assert InstanceClass.hubo().contains(instance)
>>> assert instance.sense == Sense.Minimize
>>> assert instance.objective.evaluate({0: 0}) == 2.0
>>> solution = instance.evaluate({0: 0})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 0.0)

Errors#

Mutually exclusive penalty options raise ValueError before mutating the instance.

>>> unchanged = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Maximize
... )
>>> before = unchanged.to_v2_bytes()
>>> try:
...     unchanged.to_hubo(uniform_penalty_weight=1.0, penalty_weights={7: 2.0})
... except ValueError:
...     pass
... else:
...     raise AssertionError("mutually exclusive penalty options were accepted")
>>> assert unchanged.to_v2_bytes() == before
to_qubo(uniform_penalty_weight: Optional[float] = None, penalty_weights: Optional[Mapping[int, float]] = None, inequality_integer_slack_max_range: int = 31) → tuple[dict, float]#

Convert the instance to a QUBO format.

Postconditions#

The driver is equivalent to QUBO Preparation followed by active-objective formatting and preserves the output semantics present on entry.

>>> import copy
>>> from ommx import DecisionVariable, Instance, InstanceClass, PreparationPolicy, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Maximize
... )
>>> explicit = copy.copy(instance)
>>> policy = PreparationPolicy.for_qubo(uniform_penalty_weight=2.0)
>>> _ = explicit.prepare(InstanceClass.qubo(), policy)
>>> expected = explicit.as_qubo_format()
>>> actual = instance.to_qubo(uniform_penalty_weight=2.0)
>>> assert actual == expected
>>> assert InstanceClass.qubo().contains(instance)
>>> assert instance.sense == Sense.Minimize
>>> assert instance.objective.evaluate({0: 0}) == 2.0
>>> solution = instance.evaluate({0: 0})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 0.0)

Errors#

Mutually exclusive penalty options raise ValueError before mutating the instance.

>>> unchanged = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Maximize
... )
>>> before = unchanged.to_v2_bytes()
>>> try:
...     unchanged.to_qubo(uniform_penalty_weight=1.0, penalty_weights={7: 2.0})
... except ValueError:
...     pass
... else:
...     raise AssertionError("mutually exclusive penalty options were accepted")
>>> assert unchanged.to_v2_bytes() == before
to_v1_bytes() → bytes#

Serialize this instance in the OMMX v1 wire format.

Errors#

Serialization raises RuntimeError whenever an output objective is present because v1 cannot represent it.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> assert instance.convert_active_objective(Sense.Maximize)
>>> try:
...     instance.to_v1_bytes()
... except RuntimeError:
...     pass
... else:
...     raise AssertionError("v1 serialization accepted an output objective")
to_v2_bytes() → bytes#

Serialize this instance in the OMMX v2 wire format.

Postconditions#

A v2 round-trip preserves both active and output objective semantics.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> restored = Instance.from_v2_bytes(instance.to_v2_bytes())
>>> assert restored.sense == Sense.Minimize
>>> assert restored.objective.evaluate({0: 1}) == -3.0
>>> solution = restored.evaluate({0: 1})
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 3.0)
unary_encode(decision_variable_ids: set[int] = set(), max_range: int = 16, atol: Optional[float] = None) → None#

Unary-encode the integer decision variables.

Unary encoding of an integer variable \(x \in [l, u]\) is to represent it by \(u - l\) bits \(b_j \in \{0, 1\}\):

\[x = l + \sum_j b_j\]

Every bit configuration maps to a valid integer in the original range, so no encoding-validity penalty or linking constraint is added. This costs linearly many auxiliary variables, so use it for narrow integer ranges.

Args:

  • decision_variable_ids: The IDs of the integer decision variables to unary-encode. If not specified (or empty), all used integer variables are unary-encoded.

  • max_range: Maximum allowed upper - lower range for each encoded variable. This also bounds the number of auxiliary binary variables introduced per integer variable.

  • atol: Optional absolute tolerance used when normalizing integer bounds before encoding. If None, uses the default tolerance.

Postconditions#

Encoding preserves existing output semantics, or captures the pre-encoding active objective when no output objective exists, while rewriting the active objective.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.integer(0, lower=2, upper=5, name="x")
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> instance.unary_encode({0})
>>> encoded_ids = instance.required_ids()
>>> assert len(encoded_ids) == 3
>>> state = {variable_id: 1 for variable_id in encoded_ids}
>>> assert instance.objective.evaluate(state) == 5.0
>>> solution = instance.evaluate(state)
>>> assert (solution.sense, solution.objective) == (Sense.Maximize, 5.0)
uniform_penalty_method() → ParametricInstance#

Convert to a parametric unconstrained instance by penalty method with uniform weight.

Roughly, this converts a constrained problem:

\[\min_x f(x) \quad \text{s.t.} \quad g_i(x) = 0 \; (\forall i), \quad h_j(x) \leq 0 \; (\forall j)\]

to an unconstrained problem with a parameter:

\[\min_x f(x) + \lambda \left( \sum_i g_i(x)^2 + \sum_j h_j(x)^2 \right)\]

where \(\lambda\) is the uniform penalty weight parameter for all constraints.

The removed constraints are stored in removed_constraints.

Note: This method converts inequality constraints \(h(x) \leq 0\) to \(|h(x)|^2\) not to \(\max(0, h(x))^2\). This means the penalty is enforced even for \(h(x) < 0\) cases, and \(h(x) = 0\) is unfairly favored. This feature is intended to use with add_integer_slack_to_inequality().

Postconditions#

Uniform-penalty conversion preserves existing output semantics, or captures the pre-penalty active objective when no output objective exists; materialization evaluates the penalty energy actively and invalidates optimality transport.

>>> from ommx import DecisionVariable, Instance, Optimality, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={7: x == 1}, sense=Sense.Minimize
... )
>>> parametric = instance.uniform_penalty_method()
>>> parameter_id = parametric.parameters[0].id
>>> prepared = parametric.with_parameters({parameter_id: 2.0})
>>> assert parametric.constraints == {}
>>> assert 7 in parametric.removed_constraints
>>> assert prepared.objective.evaluate({0: 0}) == 2.0
>>> solution = prepared.evaluate({0: 0})
>>> assert (solution.sense, solution.objective, solution.feasible) == (Sense.Minimize, 0.0, False)
>>> assert prepared.map_active_optimality(Optimality.Optimal) == Optimality.Unspecified
variable_labels_df() → DataFrame#

Decision-variable modeling-label DataFrame (id-indexed wide format).

Columns: name, subscripts, description. Index column = variable_id.

variable_parameters_df() → DataFrame#

Decision-variable parameters DataFrame (long format).

One row per (variable_id, parameter_key) pair. Columns: variable_id, key, value.

Description: type[InstanceDescription]#
MAXIMIZE: Sense#
MINIMIZE: Sense#
property active_special_constraint_kinds: set[SpecialConstraintKind]#

Read-only property.

The kinds of active special constraints this instance currently uses.

Returns the set of :class:SpecialConstraintKind values corresponding to non-empty active (non-removed) special constraint collections. An empty set means the instance has no active special constraints.

property annotations: MappingProxyType[str, str]#

Read-only property.

Returns a read-only mapping of flat annotations.

Use add_user_annotation(), metadata properties, or replace_annotations() to modify annotations.

property authors: list[str]#
property constraints: dict[int, AttachedConstraint]#

Read-only property.

Dict of all active constraints in the instance keyed by their IDs.

Each value is an AttachedConstraint: a write-through handle whose getters read from this instance’s SoA store and whose context setters write back through to it. Use detach() to materialize a Constraint snapshot if you need an independent copy.

property created: Optional[datetime]#
property dataset: Optional[str]#
property decision_variable_names: set[str]#

Read-only property.

Get all unique decision variable names in this instance

property decision_variables: list[AttachedDecisionVariable]#

Read-only property.

List of all decision variables in the instance sorted by their IDs.

Returns a list of AttachedDecisionVariable write-through handles. Each handle reads its kind / bound / label live from this instance’s SoA store and writes label updates back through to it. Handles also participate in arithmetic to build expressions (x + y, 2 * x etc.) — only their id is consumed for that, no host borrow is taken. Call detach() if you need an independent DecisionVariable snapshot.

property description: Optional[InstanceDescription]#

Read-only property.

property indicator_constraints: dict[int, AttachedIndicatorConstraint]#

Read-only property.

Dict of all active indicator constraints in the instance keyed by their IDs.

Each value is an AttachedIndicatorConstraint: a write-through handle whose getters read from this instance’s SoA store and whose context setters write back through to it.

property license: Optional[str]#
property named_function_names: set[str]#

Read-only property.

Get all unique named function names in this instance

property named_functions: list[NamedFunction]#

Read-only property.

List of all named functions in the instance sorted by their IDs.

property num_constraints: Optional[int]#

Read-only property.

property num_variables: Optional[int]#

Read-only property.

property objective: Function#

Active objective used by the solver-facing formulation.

Postconditions#

Assignment replaces the active objective and rebases subsequent output evaluation onto it.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> assert instance.objective.evaluate({0: 1}) == -1.0
>>> instance.objective = 2 * x
>>> solution = instance.evaluate({0: 1})
>>> assert instance.sense == Sense.Minimize
>>> assert (solution.sense, solution.objective) == (Sense.Minimize, 2.0)
property one_hot_constraints: dict[int, AttachedOneHotConstraint]#

Read-only property.

Dict of all active one-hot constraints in the instance keyed by their IDs.

Each value is an AttachedOneHotConstraint: a write-through handle whose getters read from this instance’s SoA store and whose context setters write back through to it.

property output_objective: Optional[OutputObjective]#

Read-only property.

Read-only output objective used by evaluate() and evaluate_samples(), if one has been captured.

Postconditions#

Absence and an explicit output objective equal to the active pair remain distinct.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=3 * x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.output_objective is None
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> output = instance.output_objective
>>> assert output is not None
>>> assert output.sense == Sense.Maximize
>>> assert output.function.evaluate({0: 1}) == 3.0
>>> assert output.preserves_optimality
>>> assert instance.convert_active_objective(Sense.Maximize)
>>> output = instance.output_objective
>>> assert output is not None
>>> assert output.sense == instance.sense
>>> assert output.function.almost_equal(instance.objective)
property removed_constraints: dict[int, RemovedConstraint]#

Read-only property.

Dict of all removed constraints in the instance keyed by their IDs.

property removed_indicator_constraints: dict[int, RemovedIndicatorConstraint]#

Read-only property.

Dict of all removed indicator constraints in the instance keyed by their IDs.

property removed_one_hot_constraints: dict[int, RemovedOneHotConstraint]#

Read-only property.

Dict of all removed one-hot constraints in the instance keyed by their IDs.

property removed_sos1_constraints: dict[int, RemovedSos1Constraint]#

Read-only property.

Dict of all removed SOS1 constraints in the instance keyed by their IDs.

property sense: Sense#

Read-only property.

Active optimization sense used by the solver-facing formulation.

Postconditions#

The property reports the active sense even when evaluation uses a distinct output sense.

>>> from ommx import DecisionVariable, Instance, Sense
>>> x = DecisionVariable.binary(0)
>>> instance = Instance.from_components(
...     decision_variables=[x], objective=x, constraints={}, sense=Sense.Maximize
... )
>>> assert instance.convert_active_objective(Sense.Minimize)
>>> assert instance.sense == Sense.Minimize
>>> assert instance.evaluate({0: 1}).sense == Sense.Maximize
property sos1_constraints: dict[int, AttachedSos1Constraint]#

Read-only property.

Dict of all active SOS1 constraints in the instance keyed by their IDs.

Each value is an AttachedSos1Constraint: a write-through handle whose getters read from this instance’s SoA store and whose context setters write back through to it.

property title: Optional[str]#
property used_decision_variables: list[DecisionVariable]#

Read-only property.