exact
eigenkit.chemistry.exact
Exact classical reference: dense matrix and ground-state energy of a qubit
Observable. For validating VQE on small systems (exponential cost — keep
n_qubits small).
dense_hamiltonian(observable, n_qubits, offset=0.0)
The 2**n_qubits × 2**n_qubits matrix of observable + offset * I.
Qubit 0 is the most significant factor of the tensor product, which matches the ordering of basis states in the simulators.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
observable
|
Observable
|
The qubit operator. |
required |
n_qubits
|
int
|
The number of qubits. |
required |
offset
|
float
|
The constant (identity) term that the mapping returned separately, added back to the energy. For a molecule, it includes the nuclear repulsion, in Hartree. |
0.0
|
Returns:
| Type | Description |
|---|---|
ndarray
|
The matrix, as a complex NumPy array. |
exact_ground_state_energy(observable, n_qubits, offset=0.0)
The lowest eigenvalue of observable + offset * I, by dense diagonalisation.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
observable
|
Observable
|
The qubit operator. |
required |
n_qubits
|
int
|
The number of qubits. |
required |
offset
|
float
|
The constant (identity) term that the mapping returned separately, added back to the energy. For a molecule, it includes the nuclear repulsion, in Hartree. |
0.0
|
Returns:
| Type | Description |
|---|---|
float
|
The ground-state energy. |