Qutip

Bug Fixes
-------
- Safer naming for temporary files. (by **Eric Giguère**)
- Better error message for failed string coefficient compilation. (issue raised by **nohchangsuk**)
- Fix `clebsch` function for half-integer (by **Thomas Walker**)
- Fix `randint`'s `dtype` to `uint32` for compatibility with windows. (issue raised by **BoxiLi**)
- Corrected `stochastic`'s heterodyne's m_ops (by **eliegenois**)
- Mac pool use spawn. (issue raised by **goerz**)
- Fix typos in `QobjEvo._shift`. (by **Eric Giguère**)

Improvements
-------
- Run the python 3.8 test in travis in linux. (by **Simon Cross**)
- Moved other tests to 3.8. (by **Eric Giguère**)
- Fix travis warning (by **Ivan Carvalho**)
- `husimi` / `wigner` functions adapted to accept half integer spin. (by **maij**)

Book keeping
--------
- Add Boxi Li to authors. (by **Alex Pitchford**)
- Deprecate graph function (by **Jake Lishman**)
- Skip tests that cause segfault on mac. (by **Nathan Shammah** and **Eric Giguère**)

++++++++++++++++++++++++++++++

Improvements
------------
- **MAJOR FEATURE**: Added `qip.noise`, a module with pulse level description of quantum circuits allowing to model various types of noise and devices (by **Boxi Li**).

- **MAJOR FEATURE**: Added `qip.lattice`, a module for the study of lattice dynamics in 1D (by **Saumya Biswas**).

- Migrated testing from Nose to PyTest (by **Tarun Raheja**).

- Optimized testing for PyTest and removed duplicated test runners (by **Jake Lishman**).

- Deprecated importing `qip` functions to the qutip namespace (by **Boxi Li**).

- Added the possibility to define non-square superoperators relevant for quantum circuits (by **Arne Grimsmo** and **Josh Combes**).

- Implicit tensor product for `qeye`, `qzero` and `basis` (by **Jake Lishman**).

- QObjEvo no longer requires Cython for string coefficient (by **Eric Giguère**).

- Added marked tests for faster tests in `testing.run()` and made faster OpenMP benchmarking in CI (by **Eric Giguère**).

- Added entropy and purity for Dicke density matrices, refactored into more general dicke_trace (by **Nathan Shammah**).

- Added option for specifying resolution in Bloch.save function (by **Tarun Raheja**).

- Added information related to the value of hbar in `wigner` and `continuous_variables` (by **Nicolas Quesada**).

- Updated requirements for `scipy 1.4` (by **Eric Giguère**).

- Added previous lead developers to the qutip.about() message (by **Nathan Shammah**).

- Added improvements to `Qobj` introducing the `inv` method and making the partial trace, `ptrace`, faster, keeping both sparse and dense methods (by **Eric Giguère**).

- Allowed general callable objects to define a time-dependent Hamiltonian (by **Eric Giguère**).

- Added feature so that `QobjEvo` no longer requires Cython for string coefficients (by **Eric Giguère**).

- Updated authors list on Github and added `my binder` link (by **Nathan Shammah**).


Bug Fixes
---------

- Fixed `PolyDataMapper` construction for `Bloch3d` (by **Sam Griffiths**).

- Fixed error checking for null matrix in essolve (by **Nathan Shammah**).

- Fixed name collision for parallel propagator (by **Nathan Shammah**).

- Fixed dimensional incongruence in `propagator` (by **Nathan Shammah**)

- Fixed bug by rewriting clebsch function based on long integer fraction (by **Eric Giguère**).

- Fixed bugs in QobjEvo's args depending on state and added solver tests using them (by **Eric Giguère**).

- Fixed bug in `sesolve` calculation of average states when summing the timeslot states (by **Alex Pitchford**).

- Fixed bug in `steadystate` solver by removing separate arguments for MKL and Scipy (by **Tarun Raheja**).

- Fixed `Bloch.add_ponts` by setting `edgecolor = None` in `plot_points` (by **Nathan Shammah**).

- Fixed error checking for null matrix in `essolve` solver affecting also `ode2es` (by **Peter Kirton**).

- Removed unnecessary shebangs in .pyx and .pxd files (by **Samesh Lakhotia**).

- Fixed `sesolve` and import of `os` in `codegen` (by **Alex Pitchford**).

- Updated `plot_fock_distribution` by removing the offset value 0.4 in the plot (by **Rajiv-B**).

Bug Fixes
-------------

- Fixed the pickling but that made solver unable to run in parallel on Windows. (Thank **lrunze** for reporting)
- Removed warning when mesolve fall back on sesolve (by **Michael Goerz**).
- Fixed dimension check and confusing documentation in random ket (by **Yariv Yanay**).
- Fixed Qobj isherm not working after using Qobj.permute. (Thank **llorz1207** for reporting)
- Correlation functions call now properly handle multiple time dependant functions. (Thank **taw181** for reporting)
- Removed mutable default values in mesolve/sesolve (by **Michael Goerz**)
- Fixed simdiag bug (Thank **Croydon-Brixton** for reporting)
- Better support of constant QobjEvo. (by **Boxi Li**)

Improvements
------------------

- QobjEvo do not need to start from 0 anymore. (by **Eric Giguere**)
- Add a quantum object purity function. (by **Nathan Shammah** and **Shahnawaz Ahmed**)
- Add step function interpolation for array time-coefficient. (by **Boxi Li**)

Improvements
------------------
- **MAJOR FEATURE**: Added methods and techniques to the stochastic solvers (by **Eric Giguère**) which allows to use a much broader set of solvers and much more efficiently.

- **MAJOR FEATURE**: Optimization of the montecarlo solver (by **Eric Giguère**). Computation are faster in many cases. Collapse information available to time dependant information.

- Added the QObjEvo class and methods (by **Eric Giguère**), which is used behind the scenes by the dynamical solvers, making the code more efficient and tidier. More built-in function available to string coefficients. The coefficients can be made from interpolated array with variable timesteps and can obtain state information more easily. Time-dependant collapse operator can have multiple terms.

- New wigner_transform and plot_wigner_sphere function. (by **Nithin Ramu**).

- ptrace is faster and work on bigger systems, from 15 Qbits to 30 Qbits.

- QIP module: added the possibility for user-defined gates, added the possibility to remove or add gates in any point of an already built circuit, added the molmer_sorensen gate, and fixed some bugs (by **Boxi Li**).

- Added the quantum Hellinger distance to qutip.metrics (by **Wojciech Rzadkowski**).

- Implemented possibility of choosing a random seed (by **Marek marekyggdrasil**).

- Added a code of conduct to Github.

Bug Fixes
-------------

- Fixed bug that made QuTiP incompatible with SciPy 1.3.

- quite.cite() is improved.

- Added matplotlib as optional dependency and updated numpy and scipy requirements.

- Fixed matrix generating coherent spin states in qutip.piqs to include complex coefficients.

Improvements
------------
- **MAJOR FEATURE**: Added the Permutational Invariant Quantum Solver (PIQS) module (**by Nathan Shammah** and **Shahnawaz Ahmed**) which allows the simluation of large TLSs ensembles including collective and local Lindblad dissipation. Applications range from superradiance to spin squeezing.

- **MAJOR FEATURE**: Added a photon scattering module (**by Ben Bartlett**) which can be used to study scattering in arbitrary driven systems coupled to some configuration of output waveguides.

- Cubic_Spline functions as time-dependent arguments for the collapse operators in mesolve are now allowed.

- Added a faster version of bloch_redfield_tensor, using components from the time-dependent version. About 3x+ faster for secular tensors, and 10x+ faster for non-secular tensors.

- Computing Q.overlap() [inner product] is now ~30x faster.

- Added projector method to Qobj class.

- Added fast projector method, ``Q.proj()``.

- Computing matrix elements, ``Q.matrix_element`` is now ~10x faster.

- Computing expectation values for ket vectors using ``expect`` is now ~10x faster.

- ``Q.tr()`` is now faster for small Hilbert space dimensions.

- Unitary operator evolution added to sesolve

- Use OPENMP for tidyup if installed.


Bug Fixes
---------

- Fixed bug that stopped simdiag working for python 3.

- Fixed semidefinite cvxpy Variable and Parameter.

- Fixed iterative lu solve atol keyword issue.

- Fixed unitary op evolution rhs matrix in ssesolve.

- Fixed interpolating function to return zero outside range.

- Fixed dnorm complex casting bug.

- Fixed control.io path checking issue.

- Fixed ENR fock dimension.

- Fixed hard coded options in propagator 'batch' mode

- Fixed bug in trace-norm for non-Hermitian operators.

- Fixed bug related to args not being passed to coherence_function_g2

- Fixed MKL error checking dict key error

Release of QuTiP 4.2.

Improvements
--------------
- *MAJOR FEATURE*: Initial implementation of time-dependent Bloch-Redfield Solver.
- Qobj tidyup is now an order of magnitude faster.
- Time-dependent codegen now generates output NumPy arrays faster.
- Improved calculation for analytic coefficients in coherent states (Sebastian Kramer).
- Input array to correlation FFT method now checked for validity.
- Function-based time-dependent mesolve and sesolve routines now faster.
- Codegen now makes sure that division is done in C, as opposed to Python.
- Can now set different controls for a each timeslot in quantum optimization.
- This allows time-varying controls to be used in pulse optimisation.

Bug Fixes
---------
- rcsolve importing old Odeoptions Class rather than Options.
- Non-int issue in spin Q and Wigner functions.
- Qobj’s should tidyup before determining isherm.
- Fixed time-dependent RHS function loading on Win.
- Fixed several issues with compiling with Cython 0.26.
- Liouvillian superoperators were hard setting isherm=True by default.
- Fixed an issue with the solver safety checks when inputing a list with Python functions as time-dependence.
- Fixed non-int issue in Wigner_cmap.
- MKL solver error handling not working properly.