# Change Log¶

Source code for previous releases can be found at https://github.com/grey-area/qcircuits/releases.

## v0.6.0, 2021/01/03¶

- Added purification of density operators.
- Added reduced density operators for states and density operators.
- Added convenience method for computing density operator from single pure state.
- Added method for computing computational basis measurement probabilities from density operators.
- More efficient partial trace for density operators.
- Tests for the above.

## v0.5.0, 2019/06/20¶

- Added density operators, along with operator application, qubit permutation, and measurement functionality.

## v0.4.0, 2019/04/22¶

- Supports Python 3.4.3
- Added phase gate, pi/8 gate.
- Added rotation gates.
- Can now add, subtract, negate, scalar-multiply states (and operators).
- State re-normalization is now done after operator application and measurement.
- New __str__ and __repr__ methods of operators and states.
- Can now get Kronecker product column vector/matrix representations of states and operators, and construct them from those representations.
- Can now compute the Schmidt number of a composite state.
- Can now permute the incoming and outgoing qubits of an operator in the same way as can be done to states.
- Can now apply d-qubit operators to n-qubit operators where n>d by supplying the indices of the higher-rank operator that the lower-rank operator will apply to. Unified implementation with implementation of applying operator to larger state, simplifying the __call__ method of Operator.

## v0.3.0, 2019/03/12¶

- Added methods to permute or swap qubits in a state
- There is now a flag when measuring the state that determines whether or not the measured qubits are removed from the state vector
- Added a method to get the adjoint/inverse of an operator
- Can now measure an arbitrary number of bits at once, in any order
- Measuring a state now modifies it, rather than returning the post-measurement state
- Operators can now be applied to qubits in arbitrary order
- Added Toffoli gate
- Loosened requirements to >python3.4.3 and >= numpy1.11.3
- Added unit tests
- Added documentation

## v0.2.0, 2019/03/09¶

- API change for Operator construction, and added documentation.

## v0.1.0, 2019/03/08¶

- Initial release.