# Optional Dependencies This module defines lazy availability testers for optional third-party dependencies. The checkers are instances of [`LazyImportTester`](https://quantum.cloud.ibm.com/docs/api/qiskit/utils#qiskit.utils.LazyImportTester) and can be used as booleans (evaluated lazily), or to raise a [`MissingOptionalLibraryError`](https://quantum.cloud.ibm.com/docs/api/qiskit/exceptions#qiskit.exceptions.MissingOptionalLibraryError) when a dependency is required. ## Available Testers ### HAS_FFSIM *= * [ffsim](https://github.com/qiskit-community/ffsim) is a high-performance simulator for fermionic quantum circuits that exploits particle-number and spin-Z conservation. [`FermionicCircuit`](../stubs/qiskit_fermions.circuit.FermionicCircuit.html.md#qiskit_fermions.circuit.FermionicCircuit) instances can be simulated using [`ffsim.apply_unitary()`](https://qiskit-community.github.io/ffsim/api/stubs/ffsim.apply_unitary.html#ffsim.apply_unitary). #### NOTE `ffsim` does not support Windows, which is why it is an optional dependency. #### SEE ALSO [`LazyDependencyManager`](https://quantum.cloud.ibm.com/docs/api/qiskit/utils#qiskit.utils.LazyDependencyManager) for usage examples and the available methods of this object. ### HAS_PYOMO *= * [Pyomo](https://www.pyomo.org/) is a Python-based optimization modeling language used to build linear and mixed-integer programs (LP/MILP) for classical solvers. #### SEE ALSO [`LazyDependencyManager`](https://quantum.cloud.ibm.com/docs/api/qiskit/utils#qiskit.utils.LazyDependencyManager) for usage examples and the available methods of this object. ### HAS_QISKIT_ADDON_SQD *= * [qiskit-addon-sqd](https://github.com/Qiskit/qiskit-addon-sqd) implements sample-based quantum diagonalization (SQD): it projects a Hamiltonian onto the subspace spanned by measured computational- basis configurations and iteratively refines that subspace via *configuration recovery*. #### NOTE `qiskit-addon-sqd` pulls in PySCF, which does not support Windows, which is why it is an optional dependency. #### SEE ALSO [`LazyDependencyManager`](https://quantum.cloud.ibm.com/docs/api/qiskit/utils#qiskit.utils.LazyDependencyManager) for usage examples and the available methods of this object.