Dimod

Fixes
- Fix `ConstrainedQuadraticModel.from_discrete_quadratic_model()` incorrectly formulating the discrete constraints. This bug was introduced in version 0.12.7.

New Features

- Implement version 2.0 of constrained quadratic model serialization. See `ConstrainedQuadraticModel.to_file()` for details.

Upgrade Notes

- Remove the `ObjectView.to_file()` method.
- Remove the `ConstraintView.to_file()` method.

New Features

- Implement `CaseLabelDQM.to_file()` when the keyword argument `ignore_labels` is true. Also make the error message clearer in the case that `ignore_labels` is false.
- Improve the performance of `ConstrainedQuadraticModel.from_discrete_quadratic_model()`.

Upgrade Notes

- Make the arguments of `DiscreteQuadraticModel.to_file()` keyword-only.

New Features

- Add `dimod::Constraint::clear()` C++ method.

New Features

- Add `dimod::ConstrainedQuadraticModel::constraints()` method that returns a view of the constraints that is easily iterated over.

- Improve the performance of fixing and removing variables from constrained quadratic model expressions.

- Implement the `Expression::fix_variable()` C++ method. Previously it would throw `std::logic_error("not implemented - fix_variable")`.

- Improve the performance of `ConstrainedQuadraticModel.fix_variable()` and `ConstrainedQuadraticModel.fix_variables()`.

- Add `inplace` keyword argument to `ConstrainedQuadraticModel.fix_variables()`.

Upgrade Notes

- Add an overload to the C++ `QuadraticModel::remove_variable()` method. This is binary compatible, but it makes `&remove_variable` ambiguous.

- The `ConstrainedQuadraticModel.fix_variables()` function now returns a `ConstrainedQuadraticModel` rather than an empty dictionary.

- Change `lp.load()` and `lp.loads()` to raise a `ValueErrorr` rather than a `RuntimeError` when given an invalid file format.

- Make `beta_range`, `num_reads`, and `num_sweeps` keyword-only arguments for `SimulatedAnnealingSampler.sample()`.

- Make `num_reads` and `seed` keyword-only arguments for `RandomSampler.sample()`.

- Make `initial_states`, `initial_states_generator`, `num_reads` and `seed` keyword-only arguments for `IdentitySampler.sample()`.

- Make `rtol` and `atol` keyword-only arguments for `ExactCQMSolver.sample_cqm()`.

Bug Fixes

- Fix `lp.load()` and `lp.loads()` functions to correctly handle maximization objectives. See [\1321](https://github.com/dwavesystems/dimod/issues/1321).

New Features

- Improve the performance of the `ConstrainedQuadraticModel.add_variables()` method.

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- Allow discrete constraints added by `ConstrainedQuadraticModel.add_discrete()` to have zero or one variables.

Upgrade Notes

- Remove the undocumented `cyConstrainedQuadraticModel.add_variable()` method.

Bug Fixes

- Fix `ConstrainedQuadraticModel.add_variable()` to raise a `ValueError` when given an inconsistent variable type. Previously it incorrectly raised a `TypeError`.

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- Fix `ConstrainedQuadraticModel.add_variable()` to raise a `ValueError` when given invalid variable bounds.