Enable partial evaluation of forward models

[amal-ghamdi]

General description of task

Allow partial evaluation of models. Let's say we have a multiple input forward model named myModel that has three inputs a, b, and c. After this update, the user is able create a partial model:

partial_model = myModel(a=1)

partial_model is, in itself, a CUQIpy model. For design details refer to section "2. Partial evaluation of the forward model" in internal design document

Definition of Done (Feature/change)

• Update model class to enable creating a partial model by supplying some of the inputs
• Thorough testing (about 600 test/test cases were added for this issue and issue Multiple Inputs: Enabling Bayesian modeling for multiple input models #655 )

Definition of Done (Mandatory)

• Documentation added (docstrings on all public methods/classes)
• Unit tests added/updated (and passing!)
• Code reviewed and approved by 2 CUQI-maintainers
• Online documentation is rendered correctly (esp. math)

Defintion of Done (Optional)

• HowTo/tutorial added

[amal-ghamdi]

@jakobsj, DoD ready for review, thanks you.

[jakobsj]

Thanks @amal-ghamdi - I'd like it if you could elaborate in the description how the new model should behave, such as

• allow being called on just the two remaining parameters
• what should happen in various non-supported cases e.g. such as trying to call the new model with the one parameter (a) that was fixed in the original model
• what behavior from the original model is copied across to the new model and what, if any, is not
• are deep copies of geometries and other stuff made (e.g. do or do they not share information afterwards, such that if you update a geometry or something else in e.g. the new model, will that also affect the old model).

[amal-ghamdi]

Thank you @jakobsj for taking a look. Based on that, I decided to update the design document to address these details. I updated the issue description to refer to the document, and the relevant section.

[jakobsj]

@amal-ghamdi Perfect thanks - DoD approved!