how to deploy pytorch neural network for production code in Unity
I have a neural network trained in pytorch that I'd like to deploy into a Unity app. What's the best way to do it? I'm also interested in allowing the user to further train the neural network in the Unity app, which I guess would require to integrate some part of pytorch into Unity (maybe there's a way to integrate pytorch's C++ / torchscript API with Unity?). If anybody has experience with this, I'd like to know what the best alternatives are.

Check out the new features in Unity ML Agents. There is an inference engine within Unity ML Agents (called Barracuda) that allows you to use pretrained models within your app. AFAIK, you can convert Tensorflow and ONNX models into Barracuda. It should not be a problem as Pytorch models can be converted to the ONNX format. You may need to retrain your model if it is directly affected by the app (for example, if it is an RL agent).
EDIT: To answer your second question, you can continue to train the model but not in real time. What you may be able to do is collect data from the user, and use that to further train the model (that is how TensorFlow Serving works). You can do that by converting the PyTorch model into a TensorFlow model via ONNX.
EDIT 2: Barracuda is now a standalone and production ready inference engine that runs exclusively on the ONNX format. Any framework that can be converted into the format (e.g. Keras, Pytorch, MXNet) will work as long as they contain the supported operators.
