eb8680

brms supports [joint model-based imputation](https://paul-buerkner.github.io/brms/articles/brms_missings.html#imputation-during-model-fitting) by allowing some response variables to be marked partially missing using the `mi()` syntax: ``` xf

Utilities for simplifying interactions between PyroSample and plates

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# Problem `PyroModule` and `PyroSample` make it straightforward to compositionally specify probabilistic models with random parameters. However, `PyroSample` has a somewhat awkward interaction with `pyro.plate`: ```py class Model(pyro.nn.PyroModule): @pyro.nn.PyroSample def...

Addresses #3385 This PR contains an initial implementation of a `PyroSamplePlateScope` handler as suggested in #3385. Still missing tests and documentation, but I thought I'd put a draft up now...