QM.fix_variable-c3040b5c3ca16c80.yaml

---
features:
  - Add ``.fix_variable()`` and ``.fix_variables()`` methods to ``ConstrainedQuadraticModel``.
  - Add ``.fix_variable()`` and ``.fix_variables()`` methods to ``QuadraticModel``.
upgrade:
  - |
    ``QuadraticViewsMixin`` now has ``.add_linear()`` as an abstract method.
  - |
    ``BinaryQuadraticModel.fix_variable()`` no longer raises a ``ValueError``
    when given a value that does not match the variable type.