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# NumPyEigensolver

class NumPyEigensolver(k=1, filter_criterion=None)

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The NumPy eigensolver algorithm.

The NumPy Eigensolver computes up to the first $k$ eigenvalues of a complex-valued square matrix of dimension $n \times n$, with $k \leq n$.

Note

Operators are automatically converted to SciPy’s spmatrix as needed and this conversion can be costly in terms of memory and performance as the operator size, mostly in terms of number of qubits it represents, gets larger.

Parameters

• k (int) – Number of eigenvalues are to be computed, with a minimum value of 1.
• filter_criterion (FilterType | None) – Callable that allows to filter eigenvalues/eigenstates. Only feasible eigenstates are returned in the results. The callable has the signature filter(eigenstate, eigenvalue, aux_values) and must return a boolean to indicate whether to keep this value in the final returned result or not. If the number of elements that satisfies the criterion is smaller than k, then the returned list will have fewer elements and can even be empty.

## Methods

### compute_eigenvalues

NumPyEigensolver.compute_eigenvalues(operator, aux_operators=None)

Computes the minimum eigenvalue. The operator and aux_operators are supplied here. While an operator is required by algorithms, aux_operators are optional.

Parameters

• operator (BaseOperator | PauliSumOp) – Qubit operator of the observable.
• aux_operators (ListOrDict[BaseOperator | PauliSumOp] | None) – Optional list of auxiliary operators to be evaluated with the eigenstate of the minimum eigenvalue main result and their expectation values returned. For instance, in chemistry, these can be dipole operators and total particle count operators, so we can get values for these at the ground state.

Return type

NumPyEigensolverResult

Returns

An eigensolver result.

### supports_aux_operators

classmethod NumPyEigensolver.supports_aux_operators()

Whether computing the expectation value of auxiliary operators is supported.

If the eigensolver computes the eigenvalues of the main operator, then it can compute the expectation value of the aux_operators for that state. Otherwise they will be ignored.

Return type

bool

Returns

True if aux_operator expectations can be evaluated, False otherwise.

## Attributes

### filter_criterion

Return the filter criterion if set.

Return type

FilterType | None

### k

Return k (number of eigenvalues requested).

Return type

int