CVRPProblem

class CVRPProblem(cost_matrix, *, demands, capacity, n_vehicles, depot=0, encoding='one_hot', constraint_penalty=4.0, objective_weight=1.0, capacity_penalty=4.0, max_steps=None)

Bases: _RoutingProblemBase

Capacitated Vehicle Routing Problem for QAOA.

Supports two encodings:

• "one_hot" — block one-hot with W-state + XY mixer.

• "binary" — compact binary (HUBO) with Hadamard + X mixer, reducing qubit count from O(N) to O(log N) per slot.

Parameters:

• cost_matrix (ndarray[tuple[Any, ...], dtype[floating]]) – Symmetric distance/cost matrix of shape (n, n).

• demands (ndarray[tuple[Any, ...], dtype[floating]]) – Customer demands (length = n_nodes, depot demand = 0).

• capacity (float) – Vehicle capacity.

• n_vehicles (int) – Number of vehicles.

• depot (int) – Index of the depot node. Defaults to 0.

• encoding (Literal['one_hot', 'binary']) – "one_hot" or "binary". Defaults to "one_hot".

• constraint_penalty (float) – Constraint penalty strength. Defaults to 4.0.

• objective_weight (float) – Objective weight. Defaults to 1.0.

• capacity_penalty (float) – Capacity penalty strength. Defaults to 4.0.

• max_steps (int | None) – Maximum route length per vehicle ("binary" encoding only). None (default) uses n_customers. Qubit count and HUBO term count both scale with n_vehicles * max_steps; lowering max_steps below a vehicle’s actual stop count renders the instance infeasible.

Attributes Summary

binary_config
decode_fn	Map a measurement bitstring to a domain-level solution.
encoding
recommended_initial_state	Recommended initial quantum state for this problem.

Methods Summary

compute_energy(bitstring)	Evaluate the objective energy for a bitstring.
is_feasible(bitstring)	Check whether a bitstring represents a feasible solution.
repair_infeasible_bitstring(bitstring)	Repair an infeasible bitstring into a feasible one.

Attributes Documentation

binary_config

decode_fn

encoding

recommended_initial_state

Methods Documentation

compute_energy(bitstring)

Evaluate the objective energy for a bitstring.

Defaults to None (unknown).

Return type:

float | None

is_feasible(bitstring)

Check whether a bitstring represents a feasible solution.

Defaults to True (unconstrained).

Return type:

bool

repair_infeasible_bitstring(bitstring)

Repair an infeasible bitstring into a feasible one.

Returns:

• repaired_bitstring: The feasible bitstring after repair.

• decoded: Domain-level solution (e.g. tour list, routes), or None if unavailable.

• energy: Objective value of the repaired solution, or None if unknown.

Return type:

tuple[str, Any, float | None]

The default implementation returns the bitstring unchanged.