How to check if a subcollection is being updated?

Hi,

I have a model containing two subcollections, one of which is initialised from a pre-trained model. Although I am passing the model (not the individual subcollection) to the trainer, but is there any way to check if both subcollections are being updated or just the non-pretrained one?

The issue names no files, tests, or entry points. Start by locating DyNet's trainer and model/subcollection update logic, then determine how to verify whether pretrained parameters are updated and document that check with a minimal example.

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