qiskit/releasenotes/notes/0.20/rust-pauli-expval-f2aa06c5b...

17 lines
828 B
YAML

---
features:
- |
The internal computations of :meth:`.Statevector.expectation_value` and
:meth:`.DensityMatrix.expectation_value` methods have been reimplemented
in the Rust programming language. This new implementation is multithreaded
and by default for a :class:`~.Statevector` or :class:`~.DensityMatrix`
>= 19 qubits will spawn a thread pool with the number of logical CPUs
available on the local system. You can you can control the number of
threads used by setting the ``RAYON_NUM_THREADS`` environment variable to
an integer value. For example, setting ``RAYON_NUM_THREADS=4`` will only
use 4 threads in the thread pool.
upgrade:
- |
Cython is no longer a build dependency of Qiskit Terra and is no longer
required to be installed when building Qiskit Terra from source.