Notebook: Learning and Evaluating a Probabilistic Circuit

[loreloc]

• Added notebook, as per title
• Implemented high-level circuit construction API for image data: the circuit_templates.image_data function in the cirkit.templates module

Closes #257 .

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 69.27939% with 243 lines in your changes missing coverage. Please review.

Project coverage is 71.08%. Comparing base (faf0c0c) to head (6cb2f8d).

Files with missing lines	Patch %	Lines
cirkit/templates/_factories.py	0.00%	54 Missing :warning:
cirkit/symbolic/circuit.py	61.73%	35 Missing and 9 partials :warning:
cirkit/templates/region_graph/graph.py	77.21%	29 Missing and 7 partials :warning:
cirkit/templates/region_graph/algorithms.py	87.03%	15 Missing and 20 partials :warning:
cirkit/backend/torch/graph/modules.py	57.89%	23 Missing and 1 partial :warning:
cirkit/templates/circuit_templates/data.py	0.00%	19 Missing :warning:
cirkit/symbolic/operators.py	14.28%	4 Missing and 2 partials :warning:
cirkit/backend/torch/compiler.py	54.54%	3 Missing and 2 partials :warning:
cirkit/symbolic/layers.py	54.54%	4 Missing and 1 partial :warning:
cirkit/backend/torch/layers/inner.py	0.00%	2 Missing and 2 partials :warning:
... and 7 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #262 +/- ## ========================================== + Coverage 69.08% 71.08% +2.00% ========================================== Files 53 47 -6 Lines 4392 4489 +97 Branches 594 647 +53 ========================================== + Hits 3034 3191 +157 + Misses 1219 1127 -92 - Partials 139 171 +32 ```

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